Tom Turpin
Professor of
Purdue University


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Flies in the face of fashion

What's Buggin You Now?





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Glowworms Glow When Frost is on the Pumpkin

One of the environmental benefits for living in temperate regions of the world is the changing of the seasons. To be sure, having four distinct seasons sometimes has drawbacks. Winter snowstorms and slick roads. Spring tornados. Sweltering summer temperatures. Wet and dreary declining days of fall. Season-wise, these are a few of our least favorite things!

But, lest we forget, seasons have upsides that compensate for these downsides. For example, fall is more than a bridge to winter. Color fall brilliant. Hardwood tree leaves turn red, yellow, and orange. "Tis the harvest season with golden pumpkins, yellow corn, brown soybeans and red apples."

Fall also brings cool days and crisp, frosty nights. The last remnants of the summer insect mob creep and crawl on warm sunny days. Ladlybugs, boxelder bugs, attic flies and queen paper wasps seek shelter from the approaching winter. Sometimes, much to our disgust, these insects end up in our homes. The last of the monarch butterflies wing their way to southern winter grounds. Wooly bear caterpillars crawl from place to place in search of a winter hideaway.

Fall is also the glowworm time of year. Glowworms are immatures of the insects that we call fireflies. Adult fireflies spent the summer months flashing in search of mates. Eggs were laid in July, August and September. The eggs hatch into larvae called glowworms. These baby fireflies grow up in wet areas, such as in marshes and along stream banks. And when the sun goes down, these insects earn their name. They glow.

Unlike adult fireflies, the glowworms give off a constant glow. At least, until they are disturbed when they douse the light. Because of the habit glowworms have of turning out the lights when something walks through their area, most people have not seen the fall show of mini-lights on stream and lake banks.

A glowworm show is wonderful to see. You just have to walk to a stream bank on a nice, dark fall evening. If it is a bright moonlit night, the lights of the glowworm are hard to spot. Once in the area, stop and stand quietly for a few minutes, then train your eyes at the edge of the water. With any luck at all, you should soon witness little blue-green lights coming on. The lights can be seen to line the creek bank, such that the water's edge is evident even on the darkest night.

Not all fireflies produce immatures that can be seen as glowworms. In some species, the glowworms stay under the soil, but even they produce light. In this case, we just cannot see it.

The term glowworm is used to describe adult light-producing insects in many parts of the world. For instance, the song "Glowworm," an adaptation of a German folksong made famous in the Unites States, was is certainly about the flying insects that we call fireflies in this country.

The same is true of insects referenced in Thomas Hardy's "Return of the Native," where insects called glowworms were used to provide light to complete a game being contested using dice. The light was necessary because a "Death's Head Moth" had flow into and put out the flame used to light the scene of the game. The moth flight would indicate summertime and the presence of fireflies, rather than the wingless immature insects we call glowworms.

In addition, the volume of light produced by fireflies is much greater than that produced by glowworms. But the glowworms produce light in much colder temperatures than do fireflies. Glowworms can be seen glowing when frost has formed on the pumpkin. Yes, the glow of glowworms is one of the last insect activities that you can observe as winter approaches. It is almost as if Mother Nature decreed that the last insect to leave each year should turn out the light!



Writer: Tom Turpin
Editor: Olivia Maddox