What a Way to Go

Nature is so much worse than science fiction.

~Quote attributed to a student in an introductory entomology course

We discovered a small caterpillar last week that was adorned with some unusual accessories, and that usually isn’t a good thing if you are a caterpillar. I think it was either a variable oakleaf, or a double-lined prominent caterpillar. Both are common species that feed on a wide variety of trees and shrubs.

Variable oakleaf caterpillar with parasites

Caterpillar adorned with green accessories (click photos to enlarge)

I have seen these bright green baubles attached to a few other caterpillars over the years, and it never ends up well.

Variable oakleaf caterpillar with parasites close up

Not the type of fashion accessory you want if you are a caterpillar

They really are beautiful in shape and color when you take a closer look. The first time I saw a caterpillar with these green blobs on its side was a few years ago. I thought they might be some sort of strange cocoon of a parasitic wasp. I was close…they are actually the larvae of a tiny parasitoid wasp in the family Eulophidae.

eulophid-wasp-pupae

Eulophid wasp pupae next to the dead host caterpillar

After watching the caterpillar for a few days, I came back to find a strange array of tiny black blobs near the shriveled caterpillar carcass.

eulophid-wasp-pupae-1

The small piles of yellow “stones” near the pupae are actually waste products

When I looked at my macro images, the small black blobs looked like some sort of macabre lawn recliner, with a tiny pile of rocks at the base. The black blobs turned out to be wasp pupae lying on their backs, and the piles of rocks are the waste products excreted by the wasp larvae prior to pupating. These are parasitoid wasps in the genus Eulophis. They feed inside their caterpillar host, mature, and then pupate in a group near the carcass of their victim. The excellent reference by Eiseman and Charney, Tracks and Signs of Insects and Other Invertebrates, refers to these bizarre creatures as “tombstone pupae”.  I find a lot of these clusters of Eulophis pupae on the undersides of sycamore leaves this time of year.

Caterpillar with Euplectrus pupae

Another strange way to go

A few days ago I found another caterpillar that had met what seemed like an unusual death.

Caterpillar with Euplectrus pupae 1

At first, I thought a fungus had attacked this caterpillar

The fuzzy texture initially caused me to think some sort of fungus had killed it.

Euplectrus wasp pupae

And what are these tiny black pellets?

But when I knelt down and took a closer look, I could see what looked like pupae inside the fuzz, as well as some tiny black pellets or balls stuck to the threads. What the heck is this? Going back to my reference book (mentioned above) for all things strange in the invertebrate world, I found a plausible answer. This caterpillar had been killed by another type of parasitoid wasp in that same family, but most likely in a different genus, Euplectrus. These larvae tend to form a cluster on the dorsal surface of the living caterpillar. When they finish feeding, they move to the underside of their deflated host, and arrange themselves in a row, and prepare to pupate. They create a gauzy, web-like cocoon, which attaches the caterpillar remains to the plant and provides a protective covering. The black pellets are the meconium, or waste products, cast out by the prepupa. It looks as though there wasn’t quite enough room under the carcass for all the wasp larvae to pupate, so some had to be elsewhere in the fuzzy covering.

How bizarre…and it is all happening just outside my door!

 

 

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