Sarah’s Birthday Caterpillar Hunt – 2022

Sarah and I traditionally conduct a caterpillar hunt on the weekend of her birthday in mid-September and 2022 was no different. This year we headed to Meramec State Park. I had recently heard of a short trail that covered the lush river bottom and contained hundreds of pawpaw trees. My hope was to find caterpillars of zebra longwing butterflies – a cat that has been elusive despite my many attempts at finding a late instar to photograph. We wound up short of this goal again, but we did find quite a few interesting species. I know Sarah will want me to mention that she did indeed win the day by finding more cats than I did. 🙂

Ceratomia undulosa (waved sphinx) in the family Sphingidae. This impressive cat was found feeding on an ash (Fraxinus sp.).
Although we strike out on the zebra longwings, searching through pawpaws still yield results with other specialist feeders, such as this lovely Dolba hyloeus (pawpaw sphinx).
Perhaps because they are so conspicuous, we often have luck finding the cats of the beautiful Apatelodes torrefacta (spotted apatelodes moth) in the Apatelodidae family. These come in two flavors – vanilla white and the more pleasing lemon chiffon pictured here.
Perhaps my favorite find of the day was this husk of an unknown caterpillar species having been preyed upon by larvae of an Eulophid wasp, likely an Euplectrus species. These wasps are ectoparasitoids that ride on the backs of their caterpillar hosts. When reaching their final stages in development, they spin webs and pupate within, using the remains of the caterpillar and their webs as cover.
Getting the lighting just right on these was challenging. Here, I tried my best to position the flash to illuminate the number of pupae residing beneath the remains of this poor deceased caterpillar.
Of course we are always on the lookout for larval members of the Limacodidae, or “slug moth” caterpillars. We found lots of saddlebacks (Acharia stimulea), including the two seen here. I’ve come to see how widely generalist this species is, having found them not only on numerous woody plant species, but in completely different environments, from dry upland woods to corn fields to humid bottomland forests like the one we were in on this day.
The monkey slug (Phobetron pithecium), purposed to be a mimic of tarantula exuvia, never ceases to fascinate me. Like the saddlebacks pictured above, the monkey slug also contains spines that deliver a toxic punch upon contact.
Here you can see the monkey slug’s appendages rising above the leaf it is feeding upon. The problem with being a generalist caterpillar is that these species need to be able to deal with a variety different toxins that reside in the mature leaves of their many host species. This is believed to be the reason it takes the larvae of the Limacodids so much longer to develop compared to similarly-sized caterpillars of other taxa. This comparatively longer development time may also be the selective force that helped drive the development of the stinging spines that are used to defend against parasitoids and other predators.

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