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Spun Glass Slug

The following animal ranks high on the list of utterly bizarre creatures, and one-ups even all of the caterpillian oddities that I assembled in THIS POST. Our strange beast comes courtesy of John Howard, who is an accomplished caterpillar hunter. It was high on his wish list of hoped for finds, and he finally scored a few days ago in Highland County (birthplace of Johnny Paycheck). Thanks to John - Howard, not Paycheck - for sharing these photos.

Photo: John Howard

Appearing crystalline and utterly unreal, this spun glass slug caterpillar, Isochaetes beutenmuelleri, looks like something created by Swarovski rather than a living, crawling caterpillar. We can see right through its feathery appendages, and it appears to have balls of molten frosted glass attached to its dorsal (top) surface.

In marked contrast to this beautiful - at least to my eyes - caterpillar, the adult is a rather Plain Jane little brown moth - certainly nowhere near as extravagant as its fascinating larva.

Photo: John Howard

Looking down on the animal, we can see right through the body and to the innards. That dark stripe running the length of the caterpillar is the gut. Leafy matter enters the anterior end, gets digested as it passes down that dark tract, and what's left emerges from the posterior end as frass - caterpillar poop.

Spun glass slugs consume the foliage of beech and various oak trees, so that's where you'll want to look. They're normally going to be found on the underside of leaves, and like most other caterpillars, are most likely to be found at night.

Thanks to John for sharing this incredible discovery and his great photos.


Do you know if it stings if you touch the body?
Jim McCormac said…
Hi Katie,

No, I don't believe spun glass slugs have a sting, or at least much of one. that can not be said of some of the other slugs!

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