Fireflies
Tom Rood, Master Gardener

July 10, 2002

Many of us as kids raised in the country or suburbs chased fireflies, or lightning bugs as old timers called them, hoping to catch a few in a glass canning jar with holes punched in the lid. We'd set the jar on the dresser or shelf and fall asleep watching the show. There are far fewer now than there used to be. This is not because we caught so many but rather manicured lawns, insecticides and perhaps those new fangled ultra-violet bug zappers have taken their toll. Out here, three of our neighbors at one time or another ran electric bug zappers all night long. Funny thing is that these same people seldom ventured out in the night so why the vengeance on our night flying insects? I do not know if the bug zappers attract fireflies but I do know that where they are operating there is noticible absence of fireflies. The field out behind a hedgerow is aglow with them but not on the side of facing the bug zapper.

Fireflies are beetles belonging to the largest scientific family with 23 genera and nearly 200 firefly species in North America (1,900 worldwide). They are carnivorous beneficial insects feeding on other insects such as cut worms, snails, slugs and other tiny animals that live in the soil. Most of the feeding takes place in the evening hours. The larvae overwinter in the soil and emerge in spring with ravenous appetites. By summer they are ready to pupate into adult fireflies which takes approximately two and a half weeks.

The cool light given off by fireflies is over 90 percent efficient as compared with the standard manmade incandescent light bulb which gives off 10 percent light and 90 percent heat energy. Firefly light is performed by a process called bioluminescence. It occurs when the organic compound luciferin and an enzyme lucifereace come together with oxygen in the abdomen of the firefly. Other insects also can produce illumination but only the firefly has figured out how to turn it on and off. When the firefly wants to flash, it sends a burst of oxygen into special cells in its abdomen called photocytes. The photocytes contain luciferin, lucifereace, magnesium, and ATP (adenosine triphosphate- common in most plants and animals). The resulting high energy chemical reaction is controlled by the amount of oxygen the firefly sends into the photocytes cells. Depending upon the species, the flash can be yellow, green or amber. These chemicals have been synthesized into common glow sticks found in many sporting goods stores.

The firefly flashes have several purposes readily recognized by other fireflies and predators. Each species has its own distinctive flash designed primarily as a mating signal. An experienced observer may be able to identify the firefly species by the time between flashes, the color of the flash and the duration of the flash. It is males flying upward that flash every 5 to 6 seconds, descending between flashes in a J like pattern. The females wait in brush and respond by flashing return signals. The males then try to find the females to mate. Females may respond more to larger flashes from larger males. The chemicals that make the light are very bitter and the flash warns predators of the bad taste. Birds avoid them and predator insects will start eating the head and work their way back dropping the abdomen. The flash is also a distress signal. Fireflies caught in spider webs or in glass jars will flash rapid signals to warn others away. There is also a species of firefly female cannibal that will mimic the flash response of other male species of fireflies. This particular female does this to attract males whose only thought is to reproduce and wind up as a meal instead. She will also devour her own mate.

After mating, the female firefly lays about 100 eggs on or in the soil. The eggs hatch into larvae in four weeks. The larvae feed until fall then burrow into the soil to overwinter.

Today's ecology teaches us to release captured fireflies back into the wild so they may continue their reproductive process to continue the species. Since fireflies are beneficial insects, farmers and backyard gardeners may want to rethink about using those electric bug zappers and using insecticides around hedgerows and ornamental trees and shrubs. Fireflies are fun to watch and catching them with the youngsters brings folks together. There is an old saying that the best things in life are free. Anything that gets us away from the electronic baby sitter and out into the wild with our children and grandchildren has to be a good thing. So, grab a canning jar, carefully poke some small holes in the lid and start searching for fireflies. Be sure to carry a good flashlight so there will be no mishaps with things waiting on the ground to trip you up.

For all your lawn and garden questions, or if you are interested in becoming a Master Gardener, call the Master Gardeners at the Cooperative Extension office 315-536-5123 leaving your name, question, phone number and a time we may return your call with the results of our research.

Cornell Cooperative Extension Yates Association
Last updated: 7/16/02

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