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.