A New Phrase for Your Personal Lexicon: ‘Butt-Mounted Glowstick’

A recently-discovered predatory glow worm from Peru. (Photo by Jeff Cremer)

“It’s not often you see a wall full of glowing predators.”

Aaron Pomerantz

Start your day the creepy way.

Sounds good. It rhymes. It’s not quite eight-thirty in the morning, and the coffee hasn’t kicked in, so silly rhymes work. Still, though, creepy is as creepy does, and it probably isn’t fair to call it creepy just because it’s a creeping, crawling, burrowing, predatory bit of nature that just happens to glow with a bioluminescence that allows us to see the internal organs lighting up.

Can we call that creepy? You know, without maligning nature? Then again, maybe we can blame Aaron Pomerantz of Tambopata Research Center. Really, what part of the idea of “a wall full of glowing predators” isn’t creepy?

Or maybe Gwen Pearson isn’t helping anything by her comparison:

The greenish worms are the larval form of a click beetle, and their glow seems to have one function: attracting prey. The larvae are more like a Tremors graboid than a Star Wars saarlac: hiding out in little tunnels with just their glowing head sticking out, their jaws are spread wide open. When a hapless insect is attracted to the light and blunders into their lair, the jaws snap shut. The glow seems to function only to attract prey, not for protection. In fact, once disturbed, the lights go out. Pomerantz said “they just sort of shut off once we pulled them out.”

Creepy, sure, but also fascinating, and as Pearson manages to make clear, delightfully so. It might well be my favorite new phrase: “Butt-mounted glowstick” is actually nostalgic, but one has to have either read Kotzwinkle’s Book of Love or watched the 1990 film directed by Robert Shaye. Never mind. Pearson continues:

Glowing beetles aren’t new to science; Railroad worms or glow worms (Phengodidae) occur here in the United States, as well as around the world. Fireflies (Lampyridae), the beetles that light up summer nights with their butt-mounted glowsticks, are familiar too. All bioluminescent insects known so far use the small organic molecule called luciferin to create light. The glow in both those groups of beetles is mostly for sex; they are flashing a “Come-hither My Body is Ready” message.

These larvae probably belong to a group of click beetles called Pyrophorini, or fire beetles. Adults have glowing spots, which … don’t honestly seem to have a function humans understand. Some fire beetle species also have glowing larvae, and one in Brazil lives in old termite nests. The larvae create an erie wall of glowing dots, first described in 1850. These are ferocious predators; an experimenter reported feeding 8 termites to one of the larvae in under a minute.

Yeah, but they were small termites.

We hope.

We might expect a made for SyFy B-class movie any time, now. You know, giant glowing click-beetle larvae eating the town. Just as long as they work in an outsized, butt-mounted glowstick.


Pearson, Gwen. “Glowing Predatory Insect Graboids”. Charismatic Minifauna. 14 November 2014.

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