Awhile back, we received an astute question from Tabitha who found some cockroaches acting really weird.
Your Name: Tabitha
Your message: Hey there!
I work in an office by a beautiful flowing creek. Every time it rains, brown roaches come to visit. This is in the Dallas, TX area. Well….this morning…I was making an effort to get rid of the dead roaches that are in our office every time it rains…and I came upon a weird posture in a roach. It was standing up, wings spread…I didn’t take a close look before I vacuumed the sucker up. Sorry, there is no love lost here. Why would they stand up like that? Could there have been two of them? were they mating or something?
As Tabitha correctly noted, this is actually a pretty good description of cockroach mating.
In the cockroach world, the girls passively court the boys by producing pheromones which lure them in. It’s a bit like the human equivalent of waving a hankercheif, or winking at a cute boy across the room. Only it’s a chemical, instead of a visual cue.
A good breakdown of the process can be seen in the National Geographic video below, which shows the mating process for the German Cockroach:
The video is very good, but it should be mentioned that it’s the female that’s calling there…not the male. Female cockroaches can even mate multiple times if they choose, instead of merely once. It depends on the female really…some females are choosy, others aren’t.
The males also don’t become ‘stuck’ on anything…she either accepts them or rejects them by repeatedly kicking them off her back. The stuff the male is lapping up is actually a contact sex pheromone…so there’s a really complicated chemical component here!
The cockroach genus Periplaneta, which contains the Smoky Brown, Australian and American Cockroaches has similar behavior…but the males do a mating dance to woo the females. Lots of insects and spiders do this, and the whole process ranges from very simple to extremely complicated.
Cockroaches fall into the simple and somewhat disorganized end of the spectrum…a bit like me on the dance floor.
So…what are these pheromones, and where do they come out of?
The glands are located in the abdomen, which requires females to lift their wings and pump their abdomens. They do this to expose the pheromone glands, and get the pheromones out. A calling female is shown in the picture at the beginning of the post.
Different cockroaches produce mixtures of different compounds, but their pheromones are pretty unique amongst insects because nothing else makes a pheromone that’s similar in terms of structure.
Sex pheromones are also extremely powerful. Male cockroaches can detect female pheromones at the parts per trillion level.
It’s interesting to note that this strong level of attraction has created some weird issues for researchers, because it’s hard to tell where the pheromone is actually produced. Early literature reports claimed that the pheromone was produced in the colon, but it appears to be produced in a pair of glands that are very close to the roach’s butt. These glands hare highlighted in red in the picture above, while the butt is highlighted in green.
The pheromones are so powerful, and so close to the butt, that anything coming out of the butt is attractive to male cockroaches. It’s unclear whether the colon produces the sex pheromone as well…or if the glands just contaminate the tissue during dissection. Either way poop, or even filter paper kept in the same cage, eventually becomes attractive to males…although they usually don’t try to mate with the stuff.
I wanted to close this by pointing out something about cockroaches that I think goes unappreciated…cockroaches are very highly social animals and have a lot of trouble when raised in isolation. In fact, male American cockroaches held in isolation from females never develop a normal response to these sorts of sexual signals. They attempt to copulate, but never learn to dance for their girlfriends.
So…let it be known that even though I have my own issues with roaches, I still think they can teach us a thing or two about romance. We both live in highly organized societies, and when it comes to love…our rules aren’t really all that different if you think about it.
In both species, learning to dance really goes a long way. 😉
Abed, D., et al. “Calling behaviour of female Periplaneta americana: Behavioural analysis and identification of the pheromone source.” Journal of insect physiology 39.9 (1993): 709-720. (Picture credit)
Liang, Dangsheng, and Coby Schal. “Calling behavior of the female German cockroach, Blattella germanica (Dictyoptera: Blattellidae).” Journal of insect behavior 6.5 (1993): 603-614.