Science Question From a Toddler: Insect Sex

Maggie Koerth-Baker is a guest blogger on Boing Boing. A freelance science and health journalist, Maggie lives in Minneapolis, brain dumps on Twitter, and writes quite often for mental_floss magazine.

My friends' 3-year-old son, Will, asks, "Do cockroaches have a penis?" This turns out to be a surprisingly difficult question to answer.

First off, most basic sources will just try to give you some fluffy answer about how to tell a boy cockroach from a girl cockroach, which doesn't have anything to do with penises (or lack thereof) at all. In fact, apparently, the easiest way to sex your cockroach is to count the number of of segments on the underside of its abdomen, according to roach expert Joseph Kunkel, a biology professor at the University of Mass., Amherst. Girls have more segments. Boys have fewer

Second, there appears to have been a lot more research done on female cockroach reproductive anatomy. And for good reason: It is more noticeably freaky. Female cockroaches carry their fertilized eggs around in these pod-like sacks called ootheca. Some cockroaches will tote the ootheca around attached to their bodies until the babies hatch. Other species, however, simply drop the ootheca off in some hidden corner, where the babies can incubate safely while you beat their mothers to death with a shoe. Stumble upon enough ootheca in the basement, and its liable to be the first thing you take to the lab.

But, while useful, this information does not answer the young man's question. For that, I had to turn to Cockroaches, a 2007 book by William J. Bell, Louis Marcus Roth, Christine A. Nalepa, and (yes) Edward O. Wilson. Their description of the male cockroach junk helpfully explained why I'd been getting so much confusing (and conflicting) information from other sources. To wit:

A number of intromittent structures in the male cockroach have been called a penis ... Although these structures may be associated with the ejaculatory duct ... penis-like organs function in some capacity other than to convey sperm directly

So there you have it. Cockroaches: They have no penis. But they do have a lot of things that are frequently called a "penis". Many of these bits and pieces seem to actually be used for cockblocking, so to speak. Let me explain. Instead of the familiar-to-us method of copulation, male cockroaches produce a hard, little packet full of sperm, called a spermatophore, which they transfer into their favorite gal. But, unless it's her first time around the block, there's a decent chance that somebody else's spermatophore is already in there. A male cockroach has a better chance of passing on his genes if he can get rid of the competing sperm. Whether hooked, whip-like, barbed or spiny, those not!penis structures are likely used by male cockroaches to clear out rival spermatophores, according to the august authors of Cockroaches, the book.

Beach-bunny cockroaches provided by kthypryn.


  1. BTW: I and the child’s mother recommend thinking twice before you Google “cockroach” and “penis” together.

    There are strange people out there.

  2. This comment contributes nothing to discussion other than a giant THANKS to Maggie for this post.

    Moderate as you will, but thanks, Maggie, for clearing up a question that I had never asked before.

  3. So, if I got this right: male cockroaches have a better chance to procreate if they fuck with other male cockroaches’ sperm? Hummmmmm… bears meditation.

  4. I don’t know why I read the whole post. I knew I was going to be oooked out by it. But I just kept reading…and reading. Even after the picture of the roaches sunbathing, I kept going. And there was the sentence I knew was coming, filled with words like “hooked” and “whip-like” and “spiny”, forcing the inevitable cockroach mating visualization. I can’t blame anyone but myself.

  5. Maggie you rock!

    THIS is why i originally started frequenting BB back in the day – to have shit i wouldn’t even THINK of dropped on me!

    NOTE: BoingBoing is still my first love.

  6. I think that counts as a penis. The bulb shape at the head of the (human) penis is actually their to help remove other people’s semen as well. (think of it as a sort of plunger action, which is pretty much why sex takes more than 10 seconds) By that measure cocroaches ?penis’? are very similar to human ones.

  7. “The bulb shape at the head of the (human) penis is actually their to help remove other people’s semen as well. (think of it as a sort of plunger action, which is pretty much why sex takes more than 10 seconds)”

    Oh boy! Oh Christ!
    Now I need to scrape a unicorn somehow FAST!!!

    j/k (almost)

  8. I agree with Studiorobot. You Rock, Maggie! By far my favorite guest blogger to date. These guys have needed someone like you.

    @GIBLFIZ – Thank you for the internal visualization of sloppy seconds – I owe you.

  9. maggie, weren’t you going to convince us you weren’t creepy? Cockroach penises ain’t the start, love.

  10. Yes! Cockroaches do have a penis, though the proper term for the portion of male genitalia that functions to directly inseminate the female is “aedeagus” – just thought that you’d like to hear it straight from the entomologist’s mouth! :)

  11. This is a lot more complicated that cockroaches. For starters, penis = “intromittent organ,” i.e. something males insert in females. It has evolved repeatedly and independently across Life. Thus, each instance might be for a different reason.
    Or, if you insist on restricting “penis” to mean what male humans have (a la Maggie), then it started back in the Mesozoic: one particularly brilliant species invented the thing, and it has been with us ever since.
    Regardless, two theories rule: one is cryptic female choice, the other is sexual conflict.
    Per (1), there is no functional difference between what boy cockroaches have and what boy humans have. Intromittent organs function to manipulate female desire such that she chooses A’s rather than B’s sperm to fertilize her eggs. This has to do w runaway sexual selection–it doesn’t matter what the doofus on the end of the thingy is, as long as she likes it or what you do with it, she will “choose” you.
    Per (2), females are fighting males over who controls a priceless resource (the future). Both are necessary to the other, but beyond that, they share few interests. Hence the remarks about scooping the previous male’s stuff out, or barbs, hooks, levers, points, and pliers. This is a much darker world view, and leads to weird, but logical, strategies like fanatic monogamy.
    Whatever, the insect “penis” has also evolved more than once, for example, in spiders, where males have no nerves in their genitalia (imagine).

  12. Wow – Okay – Band names in this thread:


    “The Entomologist’s Mouth”

    “Rival Spermatophores”


    “Isabella Rossellini’s Green Porn”

    Amazing. Thank you. That is all.

  13. An illuminating post. Even if there remains some question of sexual utility, it’s quite clear that a cockroach cannot have a “penis,” as “penises” themselves seem exclusively reserved for species that have an designated “penis” or some other organ called a “penis,” which a cockroach simply does not. At least, not according to any anatomical illustrations of cockroaches I’ve seen, and there have been a few.

    Maggie, I’d like to join the deafening chorus of people who’d like to see you stay here forever. And more posts like this, please. Also, I’d love to hear your thoughts on spiders that can catch and eat birds. Yuck.

  14. Whether penises arise, O priests, or whether penises do not arise,
    it remains a fact and the fixed and necessary constitution of being
    that all names of penises are transitory…

    and cockroaches have at least one, and arguably three, which are intromittent organs (“outies”), which they use to manipulate female genitalia (“innies”).
    What entomologists call penises has more to do with their own sensibilities than homology. You could equally well call them chopped liver. For example, daddy long legs traditionally have a “penis,” as does the ur-insect, the “bristletail” (Archaeognatha). Some entomologists just froze up in their naming organ and called them aedeagi, in some but not all groups. Unknown if all are homologous (as ours is among mammals, possibly all amniotes).


  15. You probably meant Maggie, but since you asked about spiders that can catch and eat birds yuck, I’ll just report that two groups can do this, the tarantulas or “bird eaters,” which are not very abundant and probably don’t eat all that many birds, and the giant golden orbweavers, which are, relatively speaking, abundant and will eat birds if they possibly can, which they have been regularly observed to do.
    Further, and why I bring that up, is that giant golden orbweavers also have unusual sex, which fits this thread, e.g.:

    “According to sexual cannibalism theory, male complicity in terminal mating can be adaptive when the male’s future reproductive value is low relative to the benefits of self sacrifice. Spiders and insects that exhibit male sacrifice behavior (either complicity in cannibalism or spontaneous death associated with copulation) often also have male genitalia that stereotypically become broken or disfigured the first time they are used for copulation, potentially lowering his future reproductive value.”

    That “potentially” is typical scientific understatement.

  16. The centipedes definitely count. They hang from the cave ceiling and snag the bats. Centipedes are untrustworthy.

    The Nat Geo film is a bit misleading. The orb weaver is Eriophora sp., and, true, they do sometimes eat bats. That particular bat, though, was basically flung into the web by a human. Nephila (golden silk spider) webs are a lot tougher than Eriophora, so while the latter may sometimes get lucky, Nephila could be said to routinely spin webs capable of stopping small birds.

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