Common fireflies in Iowa are 1/2 to 3/4 inch long. The body is elongate.

The thorax is cream or red with black markings and the wings are gray-black with a faint stripe down the middle and at each edge

While most people think of lightning bugs blinking through the dark summer nights, black fireflies are active in the daytime. Only the females of this sun-loving species uses their flashing light.

Lightningbug larvae and adults produce light by an interesting reaction of chemicals and enzymes. The light produced is a "cold" light; that is, the chemical reaction produces nearly all light and very little heat. The light flashing is regulated according to a genetically fixed pattern and is used by the adults for courtship. It is one of the means by which the males and females recognize members of their own species. Each species has a distinctive pattern of flashes, varying in flash number, duration, interval between flashes, motion accomplished during the flash, height of the flash above ground and so forth. The males and females recognize their own species' flash and get together as a result of the illumination.


Iowa DNR and ISU Extension