Insects That Could Star in a Horror Movie
A hornworm is covered with the cocoons of a parasitoid wasp. These young wasps will soon kill the caterpillar and move on to another host. Photo courtesy Betsy Cross
Samantha Youngblood
Parasitoids and their cannibalistic larvae evoke some grotesque Alien movie–like visuals. Unlike vampires or werewolves, they’re real, and you can find them in Hays County. Parasitoids are lurking in undergrowth, gardens, and even in plain sight.
But, first, what are they?
Most parasitoids are small insects, usually wasps, bees, or flies. They lay eggs inside (or sometimes on) other insects. Then their larvae eat the insect host from the inside out, slowly killing it.
Even naturalist Charles Darwin considered the life cycle of a parasitoid monstrous. In a famous 1860 letter to botanist Asa Gray, he wrote about Ichneumonid parasitoid wasps:
“I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars.”
Yes, they’re creepy, but…
Parasitoids are beneficial insects, serving as the natural enemies of many pest insects. For example, wasps of the genus Trichogramma are employed for the biological control of moth pests in greenhouses and vineyards, and they’re even available commercially.
Millions more wasps have yet to be discovered, and the bulk of those are expected to be parasitoids, according to Biology Professor Chris Nice of the Department of Biology at Texas State University. He has been teaching Texas Master Naturalists about insects (with a butterfly bias) for more than 15 years, and he recently presented to the Fall Class of Hays County Master Naturalist trainees.
Dr. Nice points to a praying mantis on his hand and has a walking stick on his shirt near his left collar. Photo courtesy Samantha Young
I caught up with Dr. Nice after class for his thoughts on this much-maligned member of the insect world.
What are the more common parasitoids and where might we find them in Hays County?
Dr. Nice: There are probably parasitoids everywhere in Hays County, but they are often overlooked because most are relatively small and look like very small wasps. We do have a few that might get noticed: the genus Megarhyssa includes large ichneumons that people tend to notice. We also have wasps in the family Evaniidae (ensign wasps) that are parasitoids on cockroach eggs and are very common in houses. They have an oddly shaped abdomen that they shake up and down, and are noticeable as a result. Beyond that, you really have to be paying attention.
What would you say to someone who finds parasitoids creepy or disgusting?
Dr. Nice: Get to know them. I think that applies to everything in biology that people find disgusting. As soon as one looks closer, you can see the fascinating stuff. Parasitoids are a marvel of the natural world: they are an exquisite product of natural selection and millions of years of evolution, and their biology is astounding. They are also major components of most ecosystems.
What sparked your interest in parasitoids? I heard you in class say you don’t understand why everyone isn’t fascinated by insects. I agree! What keeps you wanting to learn more and share what you know?
Dr. Nice: Parasitoids are a part of the whole fascinating world of insect biology. I have been fascinated with insects since a young age, and that interest was cemented in my undergraduate days. I looked for a PhD advisor working on insects, which is where my real focus on evolution and ecology in butterflies came from. I can talk even longer about butterflies!
What some find grotesque, others see as the exceptional value of parasitoids to humans. (Just wait until you learn about hyperparasitoids.)
For further reading, Dr. Nice recommends the Insects of North America guide, published by Princeton Field Guides.
Photo courtesy Betsy Cross