The surprisingly interesting life of a stick insect

You probably heard of stick insects before, maybe you’ve even seen them. The most common stick insects I knew growing up looked just like, well, sticks. It wasn’t until about 10 years ago that I started to notice all these different types of Phasmids (that’s their nerd name). Phasmids have all sorts of masquerade crypsis (fancy term for a type of camouflage), imitating different plants or plant parts (usually). However, it’s not only their physical appearance, they also have a specialized behavior: they stay very still. During this “adaptive stillness” they sort of go through a period of catalepsy to avoid predation. When they do move, they sort of move trying to “go with the wind” so their movement does not disrupt their camouflage.

Autotomy

As you can see these guys are very hard to detect. Often I wonder how many of them I have walked-by with complete disregard of their existence. This is also the case for their predators, but as with everything in nature, you cannot escape forever.

When a predator grabs a Phasmid by a leg, they can expand their wings to show them some colorful pattern (which they only have in their wings) as they let themselves go by letting go of that leg (just like lizard tails). Once they land (with their colorful wings hidden again), they blend in again as sticks, successfully fooling the predator! This self-mutilation is called Autotomy. Yes, they can grow their limbs back!

What’s interesting is that, according to Maginnis (2008), they perform this self-mutilation more often due to molting complications (joints getting stuck in old cuticle) than due to predation. Other species can spit some irritant substances that can cause temporary blindness on their threats (even for humans!).

Sex

These guys can have sexual reproduction, sure, but under certain conditions (like lack of males), females have absolutely no problem reproducing on their own through parthenogenesis. There’s a very high degree of parthenogenesis (this all-female asexual reproduction to produce “female-clones”) in Phasmatodea!

But there’s another aspect of their reproduction that is kind of cute, in my opinion. In some species, the eggs resemble plant seeds. But then they are at risk of seed-eating predators, right? But they know better: over several days, they walk around laying approximately one egg a day in a different place (instead of just laying a clutch of eggs). This way they increase the chances of survival of their progeny. Some species have other adaptations. They can pierce through some plants or bark to insert the eggs inside the plant tissues to protect them. Some just bury them in the ground.

Insects are ming-boggling. Hopefully you have a better appreciation for stick insects now! Have you ever seen any?

Recommended:

1. Maginnis, T.L. 2008. Autotomy in a Stick Insect (Insecta: Phasmida): Predation versus molting. Florida Entomologist 91(1).
2. Skelhorn, J.; Rowland, H.M.; Speed, M.P.; Ruxton, G.D. 2010. Masquerade: Camouflage Without Crypsis. Science 327 (5961), 51.