Written by Joe Ballenger
The release of Pokemon Go has been great for us entomologists, because we have been able to get people to realize why we love our jobs so much. The creator of Pokemon, Satoshi Tajiri, actually got the idea for the game because he liked to collect insects as a child. Consequently, virtually every aspect of the game relates to the jobs biologists do with some very striking parallels.
Entire books could be written on this topic, but the most common question I received over Twitter in the last few days has been this:
@Stylopidae do you, uh, get to fight them against each other?
— TrojanScientist (@TrojanScientist) July 11, 2016
— Joe Ballenger (@Stylopidae) July 12, 2016
There are YouTube channels where people pit random assortments of insects together in fights, but I’m not going to link them here because I view that as meaningless violence. I’m not a fan of this sort of thing, even though it is frequently mentioned in these conversations.
That being said, however, scientists do frequently pit insects against one another for scientific reasons. Insects fight in the wild for a number of reasons, and insect fighting is very important in some cultures. There are some very valid reasons to watch insects fight, and study how they do it.
So let’s explore the world of insect fighting!
For…you know, science.
Insect Fighting is Important in Many Cultures
In many cultures, particularly Asia, insects are very commonly kept as pets. Many of the insect species kept as pets are things like beetles and crickets…where males are very aggressive towards one another. The males of these insects tend to fight over territory, so the fights they’re watching are very close to the ones which happen naturally. People will bring their insects to specialized clubs, where they’re pitted against one another in sporting events.
This isn’t completely unlike a Pokemon gym. In fact, it’s very similar…and it’s probably where Tajiri came up with his idea.
Although this isn’t necessarily a science experiment, these battles are somewhat close approximations of what happens in the wild. Entomologists do study these sorts of battles to draw parallels with wild insects.
Insect Fighting…For Science!
If you’re an insect, your entire life is a struggle for survival. Insects are usually looking to kill something for food, and it pays to be able to fight back.
Fighting back against predators
Lacewings, for example, are voracious predators which make a living sucking aphids dry. Many aphids have responded by living in colonies, and evolving worker classes of soldiers which are adapted specifically to kill threats.
These soldier aphids are special, because they don’t eat. Their digestive systems have been modified for the sole purpose of injecting enemies with venom, which kills the attacker.
Keeping your house safe
It’s no secret that I love wasps, because I think it’s amazing that one animal can live inside another. It’s the most hostile environment on earth, one which is actively attempting to kill you. Wasps have their own ways to fight back against their hosts, but that’s a complicated topic for another post.
Instead, this lifestyle has another peculiarity…sometimes you end up with unexpected houseguests.
The competition for hosts between wasps is very intense. It’s not uncommon for a caterpillar to be parasitized by more than one species, a condition called ‘multiparasitism’. When this happens, the wasps are forced to kill the invader. If they don’t, the host could die from overuse and take both wasps along with it. Nobody wins in this case…someone must loose.
This is what the internet would call a BugFight. Two wasps enter, one wasp leaves…and it’s happening inside another insect!
Each wasp species has a slightly different tactic. Microplitis, for example, has larvae with huge jaws that are mostly used for killing any other invader which is in its host. Just after hatching, the babies clear the host of any invaders, and then molt into a grub-like larva which doesn’t move a whole lot. Only one Microplitis ever develops in a host, and the larvae will even kill their siblings if they need to.
The wasp Copidosoma, on the other hand, takes another approach…one similar to the aphids above. This wasp has two types of larvae: Reproductive larvae that grow into adults, and soldier larvae which die with the hosts. The sole job of the soldier larvae is to maraud around the host and kill anything which isn’t a sibling.
Copidosoma and Microplitis sometimes end up in the same host, and due to the way Copidosoma feeds…one of the wasps must be killed. Neither wasp can survive if the other species is present.
When Copidosoma and Microplitis end up in the same host, the results are very predictable. The vast majority of the time, Copidosoma wins the competition. The competition isn’t a close one, either. Over half of hosts (63%) parasitized by both species only end up producing Copidosoma. Microplitis only wins the fight about 8% of the time. Roughly one-quarter of the time, the fight ends in a draw…with both species dying inside the host.
The specialized soldier larvae function as attack dogs, and secrete chemicals which are toxic to other wasp species but spare the host. Wasps which develop in a manner similar to Microplitis, but with multiple larvae instead of one, don’t fare any better. Copidosoma dominates the larval stage against other wasps which use the larvae as a host.
Copidosoma, however, is not invincible. This wasp lays her eggs inside of the eggs of a moth, and her larvae develop in sync with the caterpillar host after it hatches. Microplitis lays her eggs inside of the caterpillar, and grows inside the caterpillar. In other words, Copidosoma has big a head start on Microplitis. Copidosoma soldiers are already present in large numbers by the time Microplitis arrives.
Copidosoma competes with another type of wasp, Trichogramma. Trichogramma only uses the eggs of the moth, and the adult wasps emerge long before the caterpillars hatch. When Trichogramma and Copidosoma end up in the same egg, Trichogramma is usually the winner.
The Bottom Line
Insect fighting is very important, from both a cultural and scientific standpoint. In the cultures where insect fights are common, they’re revered and respected on the same level most Americans appreciate cats and dogs. When insects fight in the wild there are a variety of tactics which are very similar to the stylized rock-paper-scissors model of Pokemon fight.
From a scientific standpoint, allowing insects to fight allows us to figure out why insects adopt their respective life strategies. In the wasp example above, it’s clear that Copidosoma lays her eggs inside the egg of another insect to give them time to prepare for a potential battle with another wasp. Microplitis wasps are fine combatants against other solitary parasitoids, but just can’t compete with Copidosoma.
At the same time, however, it appears that Copidosoma needs some time to get that lead. When confronted with a wasp which only needs the egg stage, the larvae pretty consistently lose that fight.
So entomologists do fight insects. Sometimes. When we allow them to fight, however, we’re always trying to answer a question about why they’ve adopted a particular lifestyle.
There’s a lot of unanswered questions about insects…and sometimes the only way to answer them is a good old-fashioned BugFight. Pokemon isn’t exactly a documentary, but there are some very close parallels to real-world tactics bugs use to fight.
- Clausen, C. P. (1940). Entomophagous insects. Entomophagous insects.
- Harvey, J. A., Corley, L. S., & Strand, M. R. (2000). Competition induces adaptive shifts in caste ratios of a polyembryonic wasp. Nature, 406(6792), 183-186.
Strand, M. R., Johnson, J. A., & Culin, J. D. (1990). Intrinsic interspecific competition between the polyembryonic parasitoid Copidosoma floridanum and solitary endoparasitoid Microplitis demolitor in Pseudoplusia includens. Entomologia Experimentalis et Applicata, 55(3), 275-284.
- Uka, D., Hiraoka, T., & Iwabuchi, K. (2006). Physiological suppression of the larval parasitoid Glyptapanteles pallipes by the polyembryonic parasitoid Copidosoma floridanum. Journal of insect physiology, 52(11), 1137-1142.
- Yamamoto, D., Henderson, R., Corley, L. S., & Iwabuchi, K. (2007). Intrinsic, inter‐specific competition between egg, egg–larval, and larval parasitoids of plusiine loopers. Ecological Entomology, 32(2), 221-228.