OCTOBER
2008

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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10-23-08

Download the audio of On Six Legs: MP3, WMV.

Last Glow of Summer Complements of Insects

Twice a year the earth experiences an equinox. That means the sun is directly overhead at the equator, so that any point on the earth has about the same amount of light and dark each day. The September equinox means that the sun is lower in the southern sky than earlier in the summer. It also means that the days are getting shorter, and the temperatures are getting cooler. In other words, the September equinox is the beginning of the fall season.
                    
The September equinox has been called the "Autumnal equinox" but that is relevant only to the northern hemisphere. That date, in the southern hemisphere, means that spring is coming. On that part of the earth, the days are getting longer, not shorter.

But here in the northern hemisphere, signs of approaching winter are not easily missed. Summer birds have taken the cue from Old Sol and are also headed to more southern climes. Plants have gone to seed. Leaves of perennial plants such as trees have traded their verdant hues for red, gold and brown earth tones. Before those dying leaves come tumbling down, they decorate the landscape in what has affectionately become known as the fall colors.

The Hoosier Poet James Whitcomb Riley captured the essence of the fall harvest season with the line: "When the frost is on the pumpkin and the fodder's in the shock." Even the "boys of summer" engaged in the national pastime of baseball are about to wrap up the annual duals on the diamond with the winner-takes-all contest called the World Series.

It is the time of the year when the teeming hoards of insects that buzzed and flitted through another summer season have been silenced by declining temperatures. The raucous insect songs that defined a summer night are reduced to plaintive chirps in a seeming swan song to the season past.

To be sure, on warm sunny fall days insects appear from hiding places to frolic or congregate in sunny spots. A cricket lucky enough to have found his way into a kitchen or basement chirps a song of apparent triumph. An occasional butterfly can be seen flitting aimlessly among summer's flowers now turned to seed. A last monarch butterfly hurries southward in a desperate attempt to make it to monarch wintering sites in the mountains of Mexico before the onset of inclement weather.

As insect life dwindles to a trickle following the September equinox, one insect shines like the dying embers of the summer fire. That insect is the glowworm. Glowworms are the larvae of beetles known as fireflies or lightningbugs.

These well-known insects have, as a result of their summer aerial forays, found mates. Female fireflies deposit eggs in the soil. These eggs hatch into glowworms, creatures that feed on slugs and snails. Glowworms, like their parents, get their name because of light production. Unlike the characteristic flashing patterns that their parents used to decorate summer nights, glowworms produce a constant glow.

Most people have not had the opportunity to witness the glow of glowworms. A friend of the old English poet Wordsworth was such a person and about Dorothy he wrote: "had never seen a glow-worm, never one, and this I knew."

These glowing worm-like creatures are commonly found along the banks of streams and ponds and in the grass along roadsides. But most of us, like Wordsworth's Dorothy, have not seen one. That is because we generally do not go out and walk around on dark fall nights.

To witness the glow of glowworms, you have to go to a creek or pond and pause for a moment and cast your gaze toward the water line of the creek. And there, outlining the water, you will notice a series of little blue-green glowing spots. Glowworms!

The remarkable thing about glowworms is that they produce light on nights too cold for other insect activity. That is partly because these insects can function at cool temperatures, but also because they live at the soil's surface and along the water where the temperature is generally higher than the corresponding air temperature.

So on a cool night when frost is forming on the grass and other insects have been rendered silent, the glowworms will be shining their little lights, the last glow of insect life for another season.

 

Writer: Tom Turpin
Editor: Olivia Maddox