Meet the Caterpillar That Could Pass for a Christmas Ornament

Spun glass caterpillar
The spun glass caterpillar is magnificent to look at, but dangerous to touch. (Photo: Igor Siwanowicz)

Crystalline creature

The spun glass moth caterpillar may look decorative, but it's dangerous.

This caterpillar belongs to the slug moth family, known for its collection of spiked, hairy and toxic caterpillars. The family is so named because the caterpillars truly resemble slugs — in their plump, flattened shapes as well as the way they move, atop a liquefied silk secretion. At barely a half an inch long, the spun glass caterpillar is a rare sight, though it lives throughout the United States, mainly feeding on the leaves of swamp oaks.

Carly Brooke of The Featured Creature aptly compares seeing these caterpillars to being at an antique shop full of fragile glassware: It's OK to look, but don't touch. If you do touch a spun glass moth caterpillar, a barb (or several!) from its spiky appendages will stick into your skin and cause severe skin irritation. But they don't always have this armor; "The Bugman" Daniel Marlos hypothesized on his website What's That Bug? that these tiny caterpillars may lose their appendages just before metamorphosis. "Many caterpillars change appearance just prior to pupation," he explained.

Losing its magnificent covering is the first step in an altogether unremarkable transformation. Though the larvae are spectacular, the adult moth is rather drab. Small and brown, with a wingspan less than an inch wide, these moths have a much different goal as they age — rather than giving Swarovski a run for the money, they prefer to go unnoticed.

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Spun glass caterpillar show in detail
The spun glass caterpillar's head is hidden below layers of spikes and spines. (Photo: Igor Siwanowicz)

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Spun glass caterpillar with hag moth caterpillar
A spun glass caterpillar shares a leaf with a hag moth caterpillar. (Photo: Igor Siwanowicz)