From the Vault: Animal Sex Cannibals

Sexual cannibalism is a rarity in the natural world, and scientists are still attempting to understand the act as practiced by mostly arachnids and insects. Why consume your mate after or during sexual intercourse? Why venture into such a scenario in the first place? Join Robert and Joe as they explore the thoroughly inhuman world of sexual cannibalism. (Originally published March 10, 2016) 

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Episode Transcript

Speaker 1 (00:05):
Hey, you welcome to Stuff to Blow your Mind. My
name is Robert Lamb and I'm Joe McCormick, and it's Saturday.
Time to go into the vault. We may get eaten alive. Well,
I think we're gonna be safe because it certainly this
episode is about sex cannibals. So the vault does contain
sex cannibals. However, they're not human. They're not human sex cannibals,
So you're not going to encounter, you know, any grotesque

(00:27):
tales of humanoid sex cannibals in this episode. Right, But
if we were like bachelor spiders, be a whole other story. Yeah,
if you were a spider listening to this podcast, then
you know, I would say, you know, proceed with caution.
This one was a lot of fun. We hope you
enjoy it too. It originally aired Thursday, March tenth. Uh

(00:49):
So i'd say, without any further ado, let's throw you
right into the sex cannibals. Welcome to Stuff to Blow
your Mind from stuff where its dot com. Hey what

(01:10):
can this stuff to blow your mind? My name is
Robert lamp and my name is Joe McCormick, and we're
gonna get right to it today because we're going to
talk about sexual cannibalism, right And I do want to
just throw out here right at the top, this is
not going to concern human cannibalism at all. I know
that in the past when we've covered cannibalistic topics, some
listeners have actually skipped the episode thinking that there might

(01:31):
be human cannibals in it. I'm just gonna let you know,
if you've made it this far, no human cannibals will
cannibals will occur in this episode. Is that some people's
big thing. It's like, Oh, you're gonna talk about cannibalism.
I can't go on. Well, you know, I mean some listeners,
some of our listeners really want the dark content, and
that's why and and and we're certainly happy to go
there and as well as strip away some of the uh,

(01:54):
the the taboo and the mystery surrounding those dark topics.
But I know that not everyone wants to go down
that path with us. So I just want to let
everyone know we're not going down the human cannibal path. Okay,
So we are going to be talking about animal sexual cannibalism,
and this is a topic that's been touched on on
the show before I Know You and Julie in the

(02:15):
past did an episode about cannibalism in the animal world,
but today we wanted to focus specifically on sexual cannibalism
because of all of the interesting evolutionary interplay here, the
sort of trade off of costs and benefits that would
lead a species to at some rate fairly often enough

(02:36):
that people would notice eat during sex, eat each other
during sex or after sex. Yeah, And it's the interesting
thing about this topic is that, on one hand, it
is very simplistic, and I'll get into the simplistic argument shortly,
but then it's also not as cut and drives. You
might think. It's scenario where they are multiple theories as
to as to how this evolved and exactly how it's working,

(02:57):
and some of those are actually conflicting theories as well.
So it's, uh, it's a subject with a lot of
meat on it, a lot of sexy meat on it. Okay,
So what's the basic gist of why sexual cannibalism happens.
This might be kind of obvious, but we should get
it on the table so that we have a place
to start. So let's say you have two spiders, and

(03:17):
they size each other up, and they say it's time
to mate, you know, we'll pass our genes on. But
some way through the mating procedure, the female sort of
grabs hold of the mail and sinks her fangs into
him and drains all of his delicious juices? Why did
that happen? And that's and that is the big question, right,

(03:39):
why does this evolve? And why does this occur? Certainly
not in every species, it's actually a very rare occurrence
in the natural world. But where it does occur, uh,
we can't help but study it well. Actually we should
start with the simple side. It's clear why this happens
from the female side. A lot of the question is
why the male would participate it in this right, But

(04:01):
but why does the female eat the male? Well? For energy?
Of course? I mean that. I mean that basically comes
down to stripping away the human complexity surrounding cannibalism in general,
because ultimately, flesh is energy, flesh is food, uh, flesh
is life. In addition, and so in addition to having
all sorts of cultural hangups about cannibalism, you know, we

(04:23):
don't have any problem wasting boatloads of food and energy, right,
So we kind of have to put that aside to
think of it. But yeah, in the in the natural world,
you see plenty of cases of just straight up cannibalism,
and it all comes down to a basic economy of
the energy. So a mother's young die, she might consume
those young because what are they now but empty vessels

(04:47):
made up of energy. Yeah, I think this is something
that's hard for us to understand because, by and large,
if you are a human being listening to a podcast,
you probably are are lucky. You live a fortunate exist
stence where you have decent amounts of access to food.
You're you're probably not living constantly at the edge of starvation,
and animals are sort of built with the assumption that

(05:11):
they will be living constantly at the edge of starvation.
If you ever you ever noticed how if you have
a dog at home, if you're out walking the dog
and there's something that smells even remotely like it might
be food, the dog's going to try to put it
in better, go ahead and get in the mouth anyway,
see what it takes. And you and I would never
think that way. I mean, it's like smells like it

(05:34):
could be food. Who knows if it would hurt me.
Better safe than sorry, I'm just gonna eat it. Um.
But in the animal kingdom, out in the wild, that
sort of strategy might make a lot more sense because
if you are constantly at risk of having your life
extinguished or your competitive power diminished by lack of access
to energy resources, you'll take anything you can get. Yeah, exactly.

(05:57):
And you know, we also have to think outside of
the the sort of human male female scenario, right and
get down to the basic reality that I feel like
is is far more obvious when you start looking at
in the world of of insects and arachnids and a
few other species, and that is that the females are
the species and the male is just this uh essentially,

(06:20):
this mutation that's necessary to enable genetic diversity through sexual reproduction.
So he's he only has this one purpose anyway, He's
just this genetic material, heat seeking missile and aid in reproduction.
So why not eat him? Right? His job is done
and there's there that's it gets to be more complex question,

(06:43):
as will explore later, But you know it makes sense
if you just look at the pure math of the scenario. Yeah,
And to get even weirder. I mean, you might be
able to say that neither the male nor the female
is really the purpose of the species. The phenotype, the body,
none of that is the species. The species is a
mean pool. It's this abstract concept. It's really more of
a movement as opposed to a physical thing. Because yeah,

(07:06):
that it's not the little creatures that exist for especially
in the insect world, often very slim periods of time.
It is that that continued movement, genetic movement through time. Yeah,
but but especially the males. You might say, like if
if there is a sexual dimorphism in the species, a
different in body, a difference in body plans between male

(07:27):
and female, and it just you look at it and
you say, wow, it really looks like there's more going
into the female. She's bigger, she has more survival capacity.
It really sometimes can look to a human observer like, well,
that's the female is what the species is, and the
male is just sort of this thing that exists to mate.
And yeah, and I think you can make a pretty
strong case for that that the female is the primary

(07:51):
member of the species. Now already we're talking I think
in sort of perhaps unscientific terms, like what we're using anthropomorphization,
and we're using our our our sort of human judgment
of how things just seem to look to us, based
on the way we think about relationships between animals, probably

(08:13):
mostly based on the way we think about relationships between humans.
And this is sort of an inherent problem in studying
things like animal mating practices and reproduction and especially especially
sexual cannibalism. It we just can't help but infuse it
with all of the sort of social markers of how
we view relationships as humans. Yeah, and that's true of

(08:36):
not only consumers, readers, outsiders, true not only of science
communicators like like ourselves, but also scientific researchers themselves. And
there was actually a paper on this, Yeah, two thousand
ten paper Sexual Stereotypes the Case of Sexual Cannibalism. This
was from the UK's University of St Andrew's School of Biology.
They looked at about they looked at a larger sample

(08:58):
than they had to whittle it down to end up
looking at around two ten relevant papers dealing with sexual cannibalism,
and they found that females were more likely to be
to be described using active words and males with reactive words,
And then a number of the words used to describe
cannibalistic females were highly loaded, suggesting a negative stereotype of
sexually aggressive females. Uh. And then the males were more

(09:21):
likely to be described as as making a sacrifice, while
the females were just you know, voracious widows. Um, that's funny.
Voracious is a word I did see pop up in
the literature, in the scientific literature on sexual cannibalism a lot.
And and there are some good points to be made
about you know, even though this is sort of a
tendency that's hard to overcome. I know we're going to

(09:43):
do it in this episode plenty. We're gonna anthropomorphize. It's
just how we talk about things, how we talk about
it's how we understand the topics, how we conceptualize them
in our head. Uh. There is a good case to
be made. I think that scientists should do their best
to avoid this. And one simple reason is that these
kind of social, really charged words are vague. Yeah, you know,
they're not. They don't they don't deal in easily reproducible quantities.

(10:07):
So if somebody wants to redo your experiments somewhere else,
can they tell what you mean by voracious. I mean,
it seems like it makes more sense to just talk
about numerical conditions. So a spider that attacks this percentage
of prey within this you know, radius of range is
is voracious. Yeah. And then I mean, just overall, it's

(10:30):
detrimental to view a species normalcy through the lens of
our own species abnormality. So because I mean, for instance,
we can study ducks without going holy crap. Can you
imagine if humans late eggs like a duck. So it's
a different creature, it's a different species. It is an
inhuman thing. And I guess anytime I study insects, I

(10:53):
always come back, maybe problematically to um the line of
of Dr Brundle in The Lie talking about uh insect
politics and about how there are no insect politicians um,
which which I think it's a great line, not only
within the context of that film, but also in terms
of looking at any of these scenarios where something through

(11:14):
our lens, through our lens of human normalcy, maybe just
really horrific and monstrous. And we want to cast this
insect as a villain, and this as a poor suffering martyr,
but it is an utterly inhuman system and there's no
getting around that. I'm sorry, I'm not listening to you
because I'm imagining the fly with a duck instead of

(11:36):
a fly. So Seth Brundole gets transformed into part duck
and he's got he's uh, he's got a bill. Well,
you know, Howard the Duck and the Fly came out
in the same year. Yeah, oh wow, Yeah, that's a
good year for film, the year for film. In fact,
we just had a how Stuff Works Now article come
out on that Send all of your Howard the Duck
hate mail to blow the mind stuff Works dot com.

(11:58):
But no. But moving on from how weird it would
be if humans were part duck, we should look at
the evolution of sexual cannibalism. We're going to talk about
some specific cases later in this episode of species that
practice it and what we have learned from them in
recent studies. But where where do we typically see sexual
cannibalism in the animal kingdom? Like, how come you don't

(12:20):
usually see a female cat eat a male cat after sex? Well,
I mean there's some biting, I think sometimes, but no,
for the most part, we're looking at insects and arachnids, uh,
spiders and scorpions being the primary of research. There's some
insects such as such as manted mant manted species, and

(12:41):
I believe there are also some uh, some evidences suggests
that there are some gastropod and copio pod cases. But
in the for the most part though, we're dealing with
especially with spiders and scorpions and and and mantis species.
We're dealing with highly solitary predatory animals, which I think
is key, especially regarding some of the theories regarding sexual cannibalism. Right,

(13:05):
so if you want to keep in mind that they
typically aren't the most social animal rights that eat each
other after sex, this might help inform our ideas about
how this evolved. Yeah, these are two anthropomorphizes. These are
loane killers. These are wanderers that are just out there
on the highway eating what they need to eat to survive.

(13:26):
I'd say, even if you don't want to infuse it
with with human concepts of good and evil, you could
easily say that sexual cannibalism is a chaotic, neutral trait. Yeah, yeah,
I would think so so m but but so, like
we've said, it is rare in the animal kingdom. You
don't see it in most species, and why is that? Well?
On one on one level, I think we definitely have

(13:48):
to again look to the solitary predatory nature of these
particular species. And then there's also just cannibalism as a whole.
If cannibalism is too essential to the ecs, then you
it eventually is going to have an economically detrimental effect. Right,
So imagine your standard sexual cannibalistic interaction. A female spider

(14:13):
as a web. Male spider approaches the web, climbs onto
the web, mates with the female, may or may not
successfully impregnate her, and the female eats the eats the
male spider kills him, drains all his fluids, gets energy
from it. But the male spider can mate no more.
His days of passing on his genes are now done.

(14:33):
So this interaction works out pretty well for the female spider.
I mean, so you can see why her genes would
encourage such an interaction. But the question is why would
the male do that? Why why does it uh genetically
can I mean again we're using anthropomorphic terms like consent,
but I would say, why do its genes consent to
this interaction where it has a strong chance of being eaten? Indeed,

(14:58):
that's one of the big questions here, and one of
the questions that a number of these theories um of
sexual cannibism evolution explore. So at this point we should
really start talking about what those theories are and uh,
and then break into some of the examples that explore
how they work. Yeah. So there are several conflicting or
competing hypotheses about the evolution of sexual cannibalism, and we

(15:22):
should say that more than one can be true in
different cases, right, Yeah, there's some overlap here for sure. Yeah,
But I think one thing to keep in mind during
these explanations is that there are different ways that evolution
can pay for a trait. Let's say you have a
trait that makes you there's something about your brain that
makes you really likely to kick people in the face

(15:44):
at the first time you meet them. Um, there there
are two ways that could come through in your genes
according to evolutionary theory. One one way is that the
trade itself is beneficial. Overall, people who kick people in
the face first time they meet just happen to have
more kids than people who don't, So it could be beneficial,
or it could it be it could be an unintended

(16:05):
side effect of a very beneficial trait. So it could
be that there's actually not a good there's nothing good
that comes from kicking people in the face when you
first meet them, But you're really good at kicking people
in the face the rest of the time, exactly, So
you're much much better at defending yourself against predators. So
you just happened to be kicking crazy and and this

(16:26):
is just sort of and you're so good at defending
yourself for predators, this kicking genes survives even though it's
not particularly helpful in the case of kicking strangers in
the face when you first meet them. So the first
of these several theories we're gonna mention here is adaptive foraging.
So this one's pretty basic. Starving female mates the male

(16:47):
is there, she's hungry, she's gonna need energy. Why not
go ahead and eat him during either during the act
or immediately thereafter. Eating the male increases her chance of survival,
gives her a meal based power up uh and as
a as a as a sort of side effect to
her lover can't help produce any spawn that end up

(17:08):
rivaling her own resources. But essentially it comes down to
I'm just I'm adapting to the what food is available
to me, and here is a meal in front of
me right now. Okay, so this is sort of the
the opportunism hypothesis. It's just saying that, like, look, you know,
the meal is worth it essentially right now. Some of
the critics argue that the males in many of these cases,

(17:31):
they actually make pretty poor meals. They're not really gonna
make or break the female. But then there are cases
where they say that, hey, the female is actually able
to acquire crucial proteins or lipids from the male that
she eats that she might not otherwise get from her
standard predatory diet. Okay, So I'm thinking that this is

(17:52):
saying that the sexual cannibalism is itself an adaptation. It
is itself a trait that is encouraged because overall it's
been official to the spider gene pool. Yeah, not to
the gene pool. I mean, it's I'm not taking a
species level evolution here. It would be beneficial to the
genes themselves. In the animals that do it. Yeah, the
females who eat their male have just one little power

(18:14):
up over those who that do not. Yeah, And The
idea here is that this is very much a kicking
people in the face the first time you meet them, right,
it's a good thing. Okay. But then there's another hypothesis
that is one I've read about in some of the
studies I looked up here. It's the sort of I
think it's turned the aggressive spill over hypothesis. Uh. And
this is more that other idea we were talking about

(18:36):
that there are some traits that are very beneficial, but
they encourage side effects. So one trait, for example, might
be that a that a female is very aggressive in
chasing down prey. It has genes that lead it to
be a total killer. It's just a go getter. It
sees something moving, it's like gonna eat that. Uh. And

(18:57):
this might be very beneficial to this creature when it's
trying to survive in the wild. It's it's very good
at chasing down things, killing them and eating them. But
these same genes also sometimes they get applied in the
wrong direction. Yeah, like to anthromorphize the situation. It's it's
like imagining that the spider or the scorpion in the scenario.

(19:19):
It's like a a female wrestler who in the act
of making love cannot help, like the muscle memory, just
an instincts kick in and she has to throw a
suplex or two or put somebody in a submission. Hold. Um,
this is just the female in this scenario is just
so aggressive, just so just amped up and ready to go,

(19:39):
that the predatory nature just kicks in and she ends
up consuming the part or all of the male. Yeah. Now,
is there any evidence for this? I think there's some. Yeah,
it depends. I mean in some species of spider. Yes,
researchers have observed higher sexual cannibalism rates among females that
also attacked prey at a faster rate than other females

(20:01):
they've observed I want to talk about one of these
studies in a bit. Okay, but then another species there's
no correlation. So that's the That's one of the issues too,
is you're dealing with You're not dealing with just one
species that's engaging in sexual cannibalism. You're dealing in multiple species. Uh,
some are rather diverse from one another that have in

(20:22):
many cases independently evolved this adaptation. Yeah. Now, one one
hypothesis I saw just kind of mentioned on the internet.
But I didn't see in any of the scientific literature
I was looking at was the mistaken identity hypothesis. I
couldn't tell if there's really anything to this the I
saw it mentioned. I mean, the basic idea here is
the female is saying, are you food? Are you my lover? Well,

(20:44):
let me just take a bite out of you. I
can't tell. I guess you're my enemy. I'll just bite
into you. Uh. The only place that I saw this,
and this is the person who kicks people in the
face because he's near sighted, right exactly, enemy or lover.
I think enemy, I'm gonna kick Yeah. So the only
place I saw this mint and was in um uh
Knwyn Blake Subtle's paper The Evolution of Sexual Cannibalism. Uh.

(21:07):
And he said that there's just no empirical evidence to
support this theory. Uh. For instance, he says that the
the Fight a Puss Spiders offer a strong argument against
mistaken identity because, particularly among the Salta sids, you have
the highest visual acuity of all aractans. That's I think

(21:29):
that's jumping spiders right. Yes, And he tells us that
when you take into account um cannibalism during and after
copulation that would seem to even further eliminate the possibility.
So that the idea here is that, yeah, they're not
just blind dummies in these cases. They they have senses
available to them to determine if this is a member

(21:50):
of their own species or a solid outsider prey species. Ye. Now,
of course, one other hypothesis we could say competes with
these and and maybe sometimes overlaps with them, is that
it's just it's sexual selection. Yeah, it's it's females being
choosy about which males they mate with or whether intentionally

(22:12):
or not um and this is encouraging pairing with stronger
or fitter or more appropriate males through a tendency to
eat the males. Yeah, it's just it's kind of a
it's not it's not me, it's you scenario. So I'm
going to eat you instead. You're not really uh, you're
not really husband material. Maybe you're more meal material. Right.

(22:37):
So yeah, that the basic hypotheses here entails the notion
that the cannibal female just rejects unacceptable males and eats them.
And it's smaller unfit males are better suited as meals.
Larger ones are the better mates, though you also see
this reversed in some cases with females favoring smaller mates. Uh. Again,
it kind of depends on the species, right. Well, as

(22:58):
we know from so many great evolutionary biologist before, it's
not always the strongest, that's the fittest. The bigger doesn't
always necessarily mean better. Fitter can mean a lot of
different things in different environments, And the environment can include
the sexual selection environment, the gene environment in which you're competing. Yeah,
and the mere fact that both varieties survive often indicates

(23:21):
that both are valued forms of that species. Uh. And
there are a number of different mate choice splinter theories
as well, um running the anthropomorphic gamut for all the
reasons you might you know, mate reject or cannibalize your
spider lover so that you have it. Are those are
the basic theories regarding sexual capitalism. All right, So now

(23:44):
I think it's time to take a quick break. But
when we come back, we're going to take a look
at our rogues gallery of cannibals. All right, we're back.
Who do we have for Joe? Well, I thought it
would be interesting because of a specific study I found

(24:05):
to look at the cannibalistic burrowing wolf spider, the Lycosa Hispanica.
And this is from a paper called does female personality
determine mate choice through sexual Cannibalism? It was published in
the journal Ethology in and Uh. It was carried out
by some research group at the Experimental Station of arid

(24:27):
Zones E Z A C, S I C in Spain.
And and here's what's going on. Sometimes you want to
eat your mate, but you cannot wait for the mating.
This is a problem because obviously, so we've talked about
the benefits for the female of sexual cannibalism. She gets
to mate, and she gets to pass on her genes,

(24:49):
and she also gets a meal. And we've been debating
the benefits for the male. But what if the female
eats she wants to eat the mate so bad that
she eats him before where they mate. I mean, that
seems like a maladaptive It would seems like it's gotten
out of control here. Yeah, And what they found is

(25:10):
that this happens a lot. Actually, So sometimes this specific tarantula,
this wolf spider, doesn't even wait for sex before eating
the potential mate. So why is that what determines if
the female wolf spider attacks a potential mate before the mating.
Is it how hungry she is? If so, this would

(25:31):
support the adaptive foraging hypothesis perhaps, or is it her
personality and if that's the case, it might support the
aggressive spillover. Is it the fitness of the male. This
might support some form of sexual selection or mate choice.
So the researchers decided to try to isolate these and
figure out which one is the most likely. So they

(25:53):
studied a group of female wolf spiders to see how
aggressive they were in feeding. And some were in mainly
aggressive that they were just going to town immediately on
any prey such as beatles, while others were more cautious
or they used the term docile, which I thought was funny.
Essentially more reticent hunters. They just didn't jump on prey

(26:15):
quite as quickly. And then they took these same females
they had studied and offered the females a random selection
of males for mating to see what would happen. Uh,
And you know what, the female personality actually seemed to
play a big role. So I want to read a
quote from a press release by one of the study authors,
Reuben robin Ada bueno uh, And the author said more

(26:39):
cannibalistic females were also more voracious towards their prey and
thus better nourished. This is surprising since they have more
nutritive resources to invest in their offspring before finding the
first males, and then said their priority should be ensuring
the firm spertilization of their eggs instead of eliminating their
potential donors. So this is kind of counterintuitive. You might

(27:02):
expect that the hungry or the female, the more likely
she would eat the male, but that's not what they found.
And the more aggressive females they pounced on the prey more,
they also ate more, They were less hungry, and they
were more likely to attack, kill, and eat the males.
So it sounds a little bit more like aggressive spill

(27:24):
over to me. Yeah. So, unless it's an aggressive spill over,
it would seem to be evolutionarily counterintuitive. She she's well nourished,
she should be prioritizing the fertilization of her eggs. Instead,
she just kills and eats her potential mates. But this
makes it look like baseline predation tendencies play a larger
role in whether or not the male gets eaten. Uh,

(27:47):
though you could possibly also look at this and interpret
it as a form of mate testing, Like you know,
the weaker males are the ones who are more likely
to get eaten. Alright. The next one you have here
is the raft spider, and this is UH Dolomedes fimbriatis.
And according to a two thousand fifteen study from the

(28:08):
University of Melbourne, these spiders do seem to be testing
the males and this would be mate fitness rather than
engaging in an aggressive spill over. Okay, how does this work? Well,
this is how they they They studied it. They watched
a bunch of spiders mate, of course, yes, they watched Yeah.
The first trial consisted of eleven saw that eleven of
sixteen females copulated, then attacked the males during or immediately

(28:32):
after copulation. Uh. Four of these attacks were fatal. Then
they did a second trial where six of eight females
that copulated attacked the males with two fatalities. So this
is interesting even in these uh. I think one thing
we should point out is that even in these species
that practice sexual cannibalism, it doesn't always happen, right, Yeah,
So in these cases, aggression level did not seem to

(28:56):
play a factor. So again they're they're looking at how
aggressive a hunters. This female appear to be outside the
context of mating. Rather male size, female age, and her
virginity seem to be more important factors, So females were
marginally more likely to attack smaller males. I don't know
if there's another word for this, but I kept seeing

(29:17):
this pop up over and over again. The virginity of
a spider. It just seems like it would that seems
like such a human word. Uh, Like it's weird to
think of a spider. I don't know, it would just
seem to make more sense to say, a spider who
had not yet made it. Yeah, spider virginity, or certainly
virginity of a spider sounds like a wonderful name for

(29:37):
a short horror collection, but actually will explore it in
a in another example I'm gonna get to in a bit,
you'll see where spider virginity, for lack of a better word,
does become more of an important consideration in sexual cannibalism. Yeah. Now,
one other interesting consideration to take into account is the

(29:58):
male decision in making process in sexual cannibalism cases. So
So a male is approaching a potential mate. He I
want to say he knows. I mean again, it's an insect,
so he probably doesn't really consciously know, but something about
his behavioral programming quote knows that he might get eaten

(30:19):
in some scenarios. So he has to do a kind
of behavioral cost benefit analysis. What what makes a delicious
bachelor insects decide to roll the dice with a hungry
female in the case of something like a praying mantis,
where the female in many cases eats the male during
or after sex. So there's a paper published in Plos

(30:43):
one that explores these decision factors and make choice in
sexual cannibalism UH in praying mantis is is called low
mate encounter rate increases male risk taking in sexually cannibalistic
praying mantis. UM. So you've got a male of a
ring mantis species like tin Odera sinensis and this is

(31:04):
this is a common praying mantis. I think it's referred
to as Chinese mantis. But it UH it has to
make a calculation of risk versus reward when approaching a female. Now,
I've read in one source that about sixteen percent of
the time a male of this species copulates with a
female in the wild, he gets slaughtered and eaten. So
those aren't good numbers. I mean, you wouldn't want to

(31:26):
copulate if you've got slaughtered sixteen percent of the time.
Uh So there's a chance of getting eaten, But of
course there's also the positive, a chance of reproducing. So
how does the male decide whether to roll the dice?
And the authors of this study point out two major
factors to consider. Number one is the level of predatory
risk imposed by the females, so some females are more

(31:49):
likely to eat you than other ones. And number two
is the frequency of mating opportunities for the males. How
many chances has this male had to copulate with other females.
So to study these things, the researchers artificially controlled the
dating pool. Essentially, specifically, they allowed some males of this
praying man of species to encounter and court more females

(32:11):
than others, and then they controlled the risk of predation
by the females on the males. One thing to notice
that a male a male can tell when a female
is hungry, and the hungrier she is, the more cautious
they are. However, what they found is that if the
male is sex starved, he will take risks with hungrier females.

(32:33):
And in the wild, it's worth pointing out, as we
said earlier, most of the time you're going to be
on the verge of starvation. Females in the wild are
usually hungry. So what what did they find? They found
sexually frustrated males are and those are again sorry anthropomorphine language.
The males who had had fewer chances to encounter females
in court them the ones that are sexually frustrated, We're

(32:55):
willing to take more risks with more dangerous females in
return for chances to mate. And the males who had
had more time around females that had been exposed to
more females, they were more cautious, approached the females more
slowly and stayed farther away. Um. And the ones who
had not been exposed to females, they basically just said
to hell with it and they ran in there. Okay,

(33:17):
So yeah, it comes down to what kind of risk
are they willing to take to carry out their genetic mission. Yeah,
And then there was also a second experiment where the
researchers tried this with hungry females and well fed females,
and they found that the hungry females plus sexually frustrated
males that that combination did in fact lead to cannibalism.

(33:37):
Uh they said, quote greater risk taking behavior by males
with low mate encounter rates resulted in high rates of
sexual cannibalism when these males were paired with hungry females.
So it essentially paints a picture of how to make
a male praying mantis suicidal. You take away his access
to to lady friends. There you go, Okay, but we

(34:00):
should look, we should get back to some spiders because
the classic example of sexual cannibalism in the wild is
going to be the black widow. But but let's let's
look at a relative of the black widow. That's right,
We're gonna look at red back spiders, who are relatives,
and they have males. They're seemingly quite willing to take
the risk of being cannibalized. It's another one of these

(34:20):
species where we see some some rather intense uh sexual
dimorphism here because the uh, the the the females are
are far larger while the males are tiny. About the
size of a grain of rice. Females live for up
to two years, while males generally only make it four
to eight weeks. Oh man, Yeah, so so that's one example.

(34:42):
Like we were talking about at the beginning, like we
we can't help but overlaying our sort of social values
onto the lives of these insects. But it really does
look there like the female is what's being valued somehow
by nature and the males just kind of there to
provide some sperm and disappear. Yeah, and then you know
it also comes from our attachment to life, I think too,

(35:03):
where you say, well, one lives longer, one's got a
bigger body, one seems to have more of a sensory
experience of the world, whereas I mean, it really comes
down to they each have their genetic mission, they both
carry it out. Ultimately, Hey, you could say the male
wins because he did it faster, he got to the
finish line, mission accomplished. Uh, no longer wasting resources. But

(35:26):
during copulation among the red back spiders, the smaller male
spider positions itself above the female's jaws. And this apparent
to male here I am, yeah, here, i am, I'm
right here, and this apparent male complicity. Complicity and sexual
cannibalism is favored by sexual selection because cannibalized spiders receive
a number of a paternity advantages. Oh really, so they're

(35:49):
they're documented cases here that show that it's better to
be cannibalized. So it would seem so genetically better, not
so much for the individual. Yeah, but again then we're
being we're rejecting conscious experience onto these these guys. So
cannibalized males copulate longer and they fertilize more eggs than
those who survive. Okay, so that's one advantage. Another advantage,

(36:13):
females are more likely to reject subsequent suitors after consuming
their first mate. Uh. And these results represent to empirical
evidence for uh, what is sometimes referred to as male
copulatory suicide as an adapted behavior. And of course, but
of course that's a highly anthropomorphizing term, so too. Back

(36:34):
to our analogy that this is again saying, this strangely
counterintuitive seeming behavior is itself being selected for. It's not
like a byproduct of something, It is itself the trait
that's beneficial. Kicking people in the face is good, yes,
And then there's this uh, they deposit a sperm plug
and so this is a small part of their copulatory

(36:57):
organ that stays inside the female uh. And then it
prevents any future males from successfully fertilizing her eggs, meaning
that males have to mate with a virgin spider to
maximize their reproductive success. So competition is tough then for
the male redback spider for a couple of different reasons here,

(37:18):
And they only get that one mating opportunity to carry
it out. That's it. And given the whole sperm plug thing,
they have to act fast and they also might get eaten,
so so be it. But they also have to make
sure that they have enough energy to carry out the deed. Interesting, yeah,
and this is so they might not they might fail,
they might be too weary to survive the copulation long

(37:40):
and or not survive, but to perform the copulation correctly right,
And this is where we get into I think it's
helpful to think of the mail and a weaponized sense
as a he is. He is a warhead, that is
that has sent on a mission to reach a destination.
He has to have the appropriate navigational tools and fuel
to to reach that death donation. But as it is

(38:02):
with you know, in rocketry, you you don't you don't
want to supply too much fuel. You want just enough
fuel to get where you're going, right, And that actually
plays into the development of the male redback spider. According
to a two thousand and six University of Toronto study,
the speed of their development actually depends on the density
of females in their surroundings. When males can smell females

(38:25):
in abundance, they develop rapidly, settling for a smaller body
size and less fat reserves. All also that he can
get to those virgin females sooner and if there are
if there are plenty around, he doesn't need the fat
preserves in order to survive a long search for a mate.
But likewise, if he can smell uh, you know, he

(38:47):
doesn't smell any females in the vicinity or they are
very few, then they're gonna go ahead and develop those
those fat reserves so that he can actually survive a
longer trip. Oh wow, So it's sexually strategic storage of energy. Yeah, exactly.
And if there are a lot of males in the
area already, they tend to go smaller on size but
with greater fat stores to sustain them through. And I

(39:09):
love this the extended courtship rituals in which the male
has to essentially play music on the female's web, just
like strumming the chords for up to eight hours at
a time. What yeah, And if she apparently she doesn't
like the song he's playing, she doesn't necessarily eat him.
She may just swat him off the web. We we

(39:29):
are just we are jumping the anthropomorphism shark here I am.
I am so sorry to the people who don't want
to hear the anthropomorphism because we have gone off the deeper.
How is there any way we could do this topic otherwise?
For some reason, it just demands this biased, inappropriate language.
I think the thing is, if you strip away the

(39:49):
anti anthropomorphism, it ultimately becomes less interesting to talk about,
less interesting to listen to, and harder to convey because
instead of saying, he plays there a song on a spiderweb,
I have to get into a far stuffier um biological
language about what's actually going on, And ultimately I'm conveying
the same thing. Like it's either you're easier just to say, hey,

(40:12):
this is gonna be a little anthropomorphic, so just be aware. Well,
I didn't mean that as a criticism. I mean I'm
doing it too. Uh yeah, I mean what what does
it take though for a spider to become good at
playing the strings? Does he have to practice? I don't know.
It's certainly not extensive practice because he really has to
jump right in there, right. Yeah. So here's one thing

(40:35):
I was wondering. It seems like in every case we
look at of sexual cannibalism, it's the female eating the male.
And this obviously makes sense because the female is the
egg carrying member of the species. So I mean, it
just wouldn't make sense for a male to eat a
female after copulation because that would destroy all chances of
of reproduction happening from you know, you would eat the

(40:57):
female and then the fertilized eggs would not survive probably,
and then what was the point of copulation? That just
seems like wasted energy resources. But is there any case
where some version of this could happen? There is? Interestingly enough,
we do find an example of reverse sexual cannibalism in
the mi Carria sociabilist spiders. It essentially boils down to

(41:20):
a form of mate male mate selection, much like that
employed by various female cannibals. So I see that if
it depends kind of when you when you discuss like
how unrealistic would male sexual cannibalism be, It kind of
depends on which theory you're throwing at it. So if
you're going with a mate selection, yeah, you could see
where a male could say, Nope, don't want to breed

(41:44):
with that that female. That breeding with that female is
not going to give me optimal results on my genetic
mission here, better off that I eat her and uh So.
In two thousand thirteen, a team of researchers from Messeric
University in the Czech Republic found that young males from
the summer generation of these particular spiders were the were

(42:06):
the most likely cannibals here, and they tended to cannibalize
older females of the previous spring generation. So male size
and aggressions seem to play a role in all of this,
uh and female virginity or lack thereof did not. So
this is another case where we're also getting a little
bit of the aggression spillover model in there as well. Okay,

(42:30):
but for the most part, it seems to come down
to mate selection. Yeah, so it seems like we've seen
a couple of scenarios where those two hypotheses are not
necessarily in conflict. They can sort of work together, right.
You know. One of the things that this is kind
of a side note, but one of the things that's
been interesting to me in looking at this research is
the different examples of uh I guess males that can

(42:51):
continue the mating process after they have been partially consumed
or dismembered. Particularly you see this with with some of
the the mantis species out there, right, some mantids, the
males can continue to mate after their their heads bitten off,
And I think this is the case with some of
the spiders too, right, they can like they can inject

(43:12):
a sexual organ into the female and then they can
basically be eaten while those individual organs are still doing
their work. Yeah. I mean, we already discussed in one
case where the female made it longer with the males
who are cannibalized. So it's kind of like, if I'm
cool again to anthropomorphize, if I'm cool with having my
head eaten off, I actually am going to get in

(43:34):
there longer doing the thing that I am designed to do.
So it makes sense, right, it makes so much sense.
It's like she's gonna eat me, but I'm gonna be
there twice as long. It all evens out. Now, there

(43:58):
was another interesting finding that I wanted to talk about briefly,
which was about sexual deception in a cannibalistic mating system. Yeah. So,
so there was a paper published in called sexual Deception
in a Cannibalistic Mating System testing the film Fatale hypothesis.
And this was by the scientist Catherine L. Berry in

(44:21):
Biological Sciences, Proceedings of the Royal Society b And this
was a study of the female false garden mantis. Now,
what the false garden mantis does is she has pheromones
that are taken as good faith signals of her fecundity,
of of how likely she is to produce numbers of

(44:42):
healthy offspring. So mantis is that are in better health,
they're in better shape, they're more well fed. They give
off pheromones that advertise to males like, hey, I'm good
to go. We we are going to have lots of
beautiful children together if you come mate with me. What
also within this mantis species, there is some rate of

(45:03):
sexual cannibalism where the female will eat the male UH
after or during copulation. So this study was supposed to
examine UH whether or not the females could lie using
pheromones about how likely they were when what and how
good health they were you know UH to to the

(45:25):
males who were coming up to them. So the females
were given different feeding regimens. Essentially some of them got
very good nutrition, others got medium nutrition, some got poor nutrition,
and some got very poor nutrition. And then males were
allowed to UH. They were they were given the opportunity
to sort of approach a female that they couldn't see,

(45:48):
they were visually obscured in the terms of the study
and UH and so they were just operating off of
these pheromones that were put out by the females. And
what the study found is that for most of these
female mantis is the rate at which the males would
approach them seemed to be indicating there was good faith
communication with the pheromones. So males were most likely to

(46:10):
approach the good the you know, the ones who had
been on a good feeding schedule, and then a little
less likely to approach the ones on the medium UH
feeding schedule. So so there was a pretty much correct
advertisement system there except for one case, and that one
case that did not fit were the females who had
had the very poor feeding schedule, the ones who got

(46:33):
fed the worst, and those actually attracted more males than
any of the other female feeding regimens, even though that
meant the females were in the least good health and
they were the least likely to produce good numbers of
healthy offspring, but they were the most in need of
a good cannibal meal, right exactly. And so a previous

(46:54):
study had found that these females were more likely to
cannibalize males the ones who had had the least to eat.
So the greer the female is, the more likely she
is to eat her mate. Now, studies necessarily or have
not necessarily found the same thing about other insects and ragnets.
But in this one particular species, it seems that despite
the fact that there's basically a correct or good faith

(47:16):
pheromone signaling system, uh, there are some cases in which
individuals will violate it in order to eat somebody interact.
So we get we get deception on top of everything
else that we're dealing with here. Now there's one more
paper I'd like to talk about that I thought was
pretty interesting. It's not directly addressing sexual cannibalism as its

(47:38):
main focus, but it had some cool observations about it.
And it's a paper called conditional monogamy Female Quality predicts
Male Faithfulness and it was published in Frontiers in Zoology
in So the premise of this paper is that males
from lots of animal species display polygony, you know, having
lots of wives, mating with more than one female, usually

(48:02):
as many females as he can. But some animal species
display I guess the inverse of that monogamy, wherein the
male only mates with one female in his entire lifetime. Now,
this might be for multiple reasons. The male might be
involved in uh for for example, parent parental duties maybe,
But there there are some species where that doesn't really

(48:24):
seem to be the case. Yet there is still just
mating with one female in the lifetime. And this would include,
especially to interest to our interests, several species of spiders.
Now that this is a quote from the paper, monogamy
is associated with curious adaptations like lifelong associations between males
and females. I like how that's a curious adaptation, but

(48:46):
also extreme sexual size, dimorphism, genital damage, and sexual cannibalism. Okay,
so that just lays out the obvious that sometimes you
meet that special person and that's the only person you
want to be with for the rest of your life.
Other times times they kill you and eat you or
damage your genitals. Yeah. So, uh so, Now, if you
look at a male spider sex organs, one thing you

(49:07):
might see is that the male spider has these two
copulatory organs called the pet a palps that are used
for copulation. These are sort of like miniature arms coming
out of the spider's head. Also, it is likely that
these organs will be damaged in mating, So essentially, the
male spider has two detachable penises available for his mating budget.

(49:31):
And the females, on the other hand, can mate multiple times.
So the female spider has a pair of incimination ducts.
These are her her mating openings, and these can be
in a sense plugged by a broken off piece of
male spider copulatory organs. That makes sense, so he can
break off part of his pet a palp in her

(49:52):
incimination duct to prevent other male rivals from successfully coming
along and mating with that same female, like a stabbing
in a Cormack McCarthy novel where they snapped the blade
off in the wound. Yeah. Yeah, it sounds pretty violent
in our terms, but but I guess this is how
the spiders work. We we shall not judge now. The
study in particular is focused on the orb web spider

(50:15):
known as the wasp spider or our guy ape bruiniqui,
and as a few mating stats from previous research show,
one is that in the laboratory, females are quote highly
cannibalistic and eight percent of males are killed during their
first copulation. That's a lot pretty high. Yeah yeah. They
also say genital damage is very common in a bruin bruiniqui,

(50:38):
and it occurs in eighty five percent of copulations into
unused genital openings, So there's a really good chance that
you get your sexual organ broken off inside the female.
And then on top of that, they say the broken
off pieces remain in the female insemination duc to nine
percent of these cases, so that these things, when they
get broken off, are highly effective in plugging the hole

(51:01):
so that other males can't come along and mate with
the same female. So that's one positive reason for detaching
one's penises. Yeah, among others, I assume h No, I
bet that's the only one. But anyway, so, since the
male sex organs tend to get broken off, he has

(51:22):
a choice. He has two of these things, and he
can spend them both on the same female. This would
be the case of monogamy, mating with only one female
in his lifetime, or he can try to mate with
two different females in his lifetime. Okay, so we see
us a form of mate selection here that he can
decide if this is definitely the one so much so

(51:43):
that he wants to double down on this mate selection,
or if he wants to save one keep one in
the chamber for labor later use. Right. It's like if
you're you know, you know, you're you're playing Roulette and
you have two chips. Do you put them on two
different numbers? Or do you put them both on the
same number. I'll in on black wa Right. So, the
researchers tested interactions between these spiders and they found lots

(52:04):
of interesting correlations. For example, the size of the male
did not seem to have any impact on the mating strategy,
but the size of the female did So when when
a male encountered a female for the first time, the
bigger the female, the more likely the male was to
use his entire mating budget on her to give her
both of his sex organs. Also, when a male mated

(52:27):
with two different females, when he decided to spread it
over two different two different numbers on roulette, the second
female he broke off a sex organ with tended to
be heavier than the first, so he would tend to
trade up for a larger female. The larger the female
usually the more fecand well like a lot of what
we've discussed here in this episode, and that that makes

(52:48):
perfect economic sense of course. Now a few other interesting
things they observed. One of them was that the rate
of sexual cannibalism they saw in their study was much
lower than what had been previously reported that number we
cited earlier. They found that the frequency of cannibalism on
the first copulation, so the first time male and female
meet up, was thirty one point four percent. So that's

(53:12):
lower than than previous studies. But there was also one
really funny complication of how this worked out. In the
lab they write, quote, the monogamous males either copulated once
M one, and this is what they called the group
M one, which are males cannibalized after a single copulation
or twice with the same female. In the M one group,

(53:34):
it cannot be decided whether males would have followed a
bigginess or monogamous tactic if only they had survived their
first copulation. So sometimes the male he gets one broken
off sex organ into the female, but then she eats
him and you can't tell whether he was planning on
using both on her or moving on. That's right, because

(53:55):
she has enacted her a mating choice exactly he can exercise. Yeah,
And related to that is that one thing they noticed
was I think this goes along with some of the
other stuff we've read. How long a male mate it
during his first copulation was directly positively correlated to the
rate of sexual cannibalism. So the longer he sticks around,
the more time he spends locking down his copulation with

(54:18):
this one female, the higher the chance that he gets
slain and devoured. All right, now, I want to read
one more long ish quote from their discussion section because
I thought it was really interesting related to what we've
been talking about today. They say, quote some of the
monogamous males were cannibalized after their first copulation, while others
used both of their mating options with the same female.

(54:41):
While the latter can be interpreted as a clear cut
male decision, So if the male uses both on the
female and then gets eaten, sort of makes sense for
him to get eaten, right, um uh, they picked back up.
Interpreting the decisions of single mated males is more difficult.
At least, some of these males may have been forced

(55:01):
into monogamy by aggressive females, while others may have chosen
to sacrifice themselves to their mating partner already during the
first copulation. Whether a male falls victim to sexual cannibalism
during the first copulation is a direct function of its duration.
Any copulation longer than ten seconds, remember that number will

(55:22):
most likely end with the death of the males. Well,
males that jump off before ten seconds have a relatively
high chance of surviving. Indeed, copulation durations of single mated
males show a high variance, which suggests that some of
them chose to copulate for longer in spite of sexual
cannibalism being the likely consequence, while others attempted to escape

(55:45):
but failed. So I don't know. I feel like that
sort of drives home that when you're speaking about evolution,
it's worth remembering that your body is sort of of
little use to your genes once you've lost all of
your reproductive potential. Us, the male individual here is is
a delivery system for the genetic material. But anyway, if
you want to read that study, it's again conditional monogamy.

(56:08):
Female quality predicts male faithfulness is pretty interesting and had
some other observations too. All right, so there you have it. Uh,
we've we've discussed sexual cannibalism, some of the theories regarding
uh it's evolutionary development or a handful of species why
it seems like it might not make sense, but but
it probably does. And of course we've engaged in a

(56:30):
fair amount of anthromomorphism. But still I felt like I
was holding back in some of so was I. Now,
if you're a professional researcher in this field, don't take
a page from us, Try to do do the right thing.
Be boring, but be accurate. I think, like an insect,
whenever possible. All right, In the meantime, if you want
to check out more episodes of Stuff to Blow Your Mind.

(56:51):
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(57:11):
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(57:34):
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