(Intro)

Emily: Hey! We're here with Corrie Moreau, who's the Curator of Insects here at the Field Museum.

Corrie: Hi!

E: Hey! And today, we're going to talk about ants!

C: And ant sex. For Valentine's Day.

E: Yeah! 'Cause there's nothing more romantic than ant sex.

C: So this is actually a worker of a turtle ant in the genus Cephalotes. One of the things I love about this ant is sort of the remarkable anatomy of it. So you see this head capsule is a totally different shape than all the other individuals in the nest. So most individuals in the nest look like this small one here, where they don't have this odd-shaped head. Where, in the larger individuals in the nest, we actually see that they have this enlarged head capsule- and you see it almost looks like a dinner plate or a saucer. That's because they block the nest entrance of the hollow twigs they live in. So they act just like a living door. So all day long, all they do is sit and block the nest entrance.

E: They just like...

C: Yes, absolutely.

E: With their face in the door. Don't they get bored?

C: Probably.

E: Probably?

C: People often think of ants as being, you know, the strong and mighty ones like this, the workers and the soldiers as being male. But it turns out almost every ant you've ever seen in your life is female.

E: No way.

C: If you've ever seen an ant without wings, it's female.

E: Why? What's the benefit of only having one sex in an entire colony?

C: So in this case, it has to do with relatedness. So you can imagine that we have all of these individuals that have forgone the ability to reproduce, to have sex. Right, so there has to be some benefit to them. And so, what happens is that sisters are more closely related to each other than they are to their brothers or even their mother.

E: Really? Why?

C: Yeah. So it's called haplodiploidy. So unlike us—where in order for a new offspring to be formed you have to have the sperm and the egg unite, and then you get half of your genome from your mom, half from your dad— in Hymenoptera, including the ants, the way that it works is that females are produced when an egg and sperm are united, but if no sperm is ever introduced to that egg, that becomes male. So a male only has half the size of the genome.

E: So, if there are no males like existing in these societies, how do they get sperm then?

C: Yeah, that's a good question. So, in the ants, about once a year, they make sexuals; or the males, and the new females—the virgin queens— and they go off on mating flights and reproduce, and then the males die almost right away. Now the female, who's mated just this once in her first year of life, she flies around and finds a new habitat, digs down and starts a whole new colony of all females. And she stores all that sperm in a special organ inside her body—it's called a spermatheca—

E: I'll play that word in Scrabble next time.

C: And then she can store that sperm for her entire life, so sometimes it's for a few years, sometimes up to 25 years. So she never leaves the nest again, she never mates again. She just lays an army of all female workers and then once a year produces sexuals.

E: So, just to clarify, she's got all this sperm stored up within her body, and she can produce females without needing to draw from that sperm bank.

C: No, the females she uses to draw from the sperm bank. The males are just eggs that are unfertilized.

E: What?

C: I know, it's cool.

E: That is crazy.

C: Yeah, yeah. And so in insects, the way that they reproduce is that the males have essentially a penis, but it's called an aedeagus, and that's the sort of delivery vehicle to the opening in the female. This is actually a female queen. You can see her sting right there? -

E: Wow. Yeah!

C: And that's what she would deliver a venom from, right? And that's right above where she can lay eggs. So actually in this case her sting is a modified ovipositor, but is now no longer used for egg laying; it's actually just used for venom delivery. These are called bullet ants. I actually have a whole giant tub of them here. These are found in Central America and South America, and they're called bullet ants because their sting is so painful it feels like you've been shot by a gun.

E: REALLY?

C: Yeah, here, you can hold one.

E: Have you ever been stung by one —I don't know if I want to hold it! Even though it's dead!

C: I have been stung by one once. It was really hot. I actually got stung right on the tip of my finger and it was like my finger had a total fever—shooting pain up my arms... it's really pretty terrible. And in this case, I mean, I got stung pretty minimally, but I know people who have been stung by like 20 at once and then had to be carried out of the rainforest.

E: Oh my gosh!

C: Yeah, it's really terrible, and then you have fevers and flu-like symptoms for several days.

E: Can you die?

C: I think the only way you would die is if you had anaphylactic shock. So just essentially if you were allergic like a honey bee. The turtle ants that I was showing you earlier, these girls here, actually have no ability to sting. Their sting's been so reduced that they don't sting, and then their jaws are so little they can't bite. They're the perfect ant: they don't bite or sting, and they're beautiful! But then another group of ants that I brought actually, are army ants, and one of the things I love about army ants is the soldiers can become so highly modified. I mean, you almost can't even recognize them, necessarily. So these are two sisters from the same colony, from the same mother.

E: Woah.

C: Yeah, exactly. So this little tiny one at the bottom: the role of that individual is really to go out and do all the foraging, the nest cleaning, the caring for the larvae. Where these big soldiers here, not only are they much bigger, but their whole role is defense. And so you can see from their mandibles or their jaws.

E: Oh my gosh.

C: Yeah, they're essentially these tusks, right?

E: Woah.

C: So they come down to these, almost like, pure spikes on the ends of their face and their jaws have become so highly modified for defense and nothing else. They can't even feed themselves anymore. I mean imagine, there's no way you can get food from here up to your mouth up there, right? So they actually rely on other workers to carry food and place it into their mouth.

E: Really?

C: Yeah! It's really amazing.

E: That's amazing! I can't imagine my sister coming up to me and like, hand-feeding me. That seems so strange.

C: Ants, it turns out, have helpful gut bacteria, just like we do, so we can actually study the bacteria using DNA-based technologies to investigate how they're actually processing the food that they bring to the colony. And one of the really cool things is that all ant species actually have mouth-to-mouth food sharing; it's called social trophallaxis, where they just essentially regurgitate to each other.

E: Really.

C: But in the case of the turtle ants in particular, because they also need to share their gut microbes, mouth-to-mouth isn't very good, so they participate in oral-anal trophallaxis to reacquire their gut microbes.

E: Wh— They like eat— They eat poop?

C: That's essentially right. So just like termites in order to re-seed their stomachs after metamorphosis, ants do that as well. So they actually have to find another individual that has a good, healthy gut community and lick the rear end of their sister.

E: Oh my god.

(Credits)

E: It still has brains on it.