Tag Archives: Glow-worms

Next up: Fall glow-worm extravaganza

Autumn happens to be quite an exciting time for fireflies. I get it – you probably can’t imagine fireflies beyond summer.  And that is when adult get all reproductive and stuff. But there’s cryptic chapter in the firefly’s life story, and it’s starting right now.

Firefly Life Cycle.png

Once mated, the female firefly will produce 30-100 eggs, laying them one-by-one in some moist dirt or moss. After a few weeks, these eggs hatch out into tiny larvae that immediately burrow down underground. Though adult fireflies only live a few weeks, their progeny will spend up to two years hanging out underground.

Larval Jaws

photo by Melvyn Yeo (Flickr)

Baby fireflies happen to be voracious predators. They’re constantly on the hunt for earthworms, snails, and any other soft-bodied prey. They attack creatures that are much bigger than themselves. How do they manage this? First, they use their sharp, sickle-shaped jaws to inject the prey with paralyzing neurotoxins. Next, they secrete digestive enzymes to liquify their prey, then they slurp it up. Earthworm smoothie, anyone?

When they’re disturbed, larval fireflies glow from two tiny lanterns located at the tip of their abdomen. All firefly larvae can light up, across 2000+ species, even when the corresponding adults cannot. So we think fireflies’ light-producing talent first evolved because it gave these juveniles some advantage.

But … what’s the point of these juveniles being so conspicuous?

We know that fireflies contain nasty-tasting chemicals that help them avoid getting eaten (see earlier post). Lots of poisonous creatures use bright coloration to warn off potential predators. Yet firefly larvae are mainly active at night or underground, where having bright colors would be futile. But a flash in the darkness would certainly do the trick – like a neon sign, it  blazes out “I’m toxic – stay away!”

So get ready to watch for firefly larvae crawling along roadsides and wooded paths, glowing dimly. Often overlooked, these juveniles should rightly be celebrated as the original inventors of fireflies’ magical lights.

pageofbats life cycle illustration

Illustration by pageofbats (Flickr)

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Fall glow-worm season is here!

Each autumn the world seems aglow with foliage and jack-o-lanterns. But they’re not the only  glowing things lighting up this season. Fall is also a great time to spot the crawling, glow-in-the-dark stage that all juvenile fireflies pass through.

Firefly larvae and pupae

Glowing firefly larvae (left) and pupae (photo by Siah St. Clair)

Hatched from eggs laid during summer months, these firefly larvae can now be seen crawling along  roadsides or wooded paths, glowing dimly from two tiny lanterns.    Photuris and Pyractomena larvae are the two types seen most often in the U.S. But one reader in Portland, Oregon even spotted  the much rarer Douglas fir glow-worm, Pterotus, along a path in Mt. Tabor Park. Continue reading