Forest Preserve District of Cook County, Illinois
Nature Bulletins
Newton Home Page

Introduction and Instructions

Search Engine

Table of Contents



Nature Bulletin No. 27   August 11, 1945
Forest Preserve District of Cook County
Clayton F. Smith, President
Roberts Mann, Superintendent of Conservation

Fireflies, or lightning-bugs, were unusually late this year. Few were seen before July 4th and in some localities they are still scarce. The firefly is a beetle, of the family Lampyridae. The adults are short-lived and eat little or no food. They are nocturnal in habit, resting on the leaves cool, damp bushes during the day. The female lays a hundred or more eggs at the base of a plant in a damp, moist place, generally near a stream. The larvae hatch and live for one or two years in the soil.

The firefly is much more efficient than man in producing a "cold light", containing no ultra violet rays, with a wavelength from 0.00051 to 0.00067 millimeters in length, pale yellowish or reddish green in color, with a light efficiency of 96%.. The ordinary incandescent light has an efficiency of roughly 10%, most of the energy being wasted as heat.

The light-producing organ is located in the sixth, or the sixth and seventh abdominal segments. Here are stored two compounds known as "luciferin" and "lucifrase". A system of fine air tubes, controlled by the nervous system, bring most air to the luciferin, oxidizing it and activating the lucifrase to produce light reflected through thin skeleton of the abdomen.

If you will notice, the firefly turns on its light when flying upward, at intervals of about 5.8 seconds. In the dark periods it coasts downward again. You may also have noticed that hundreds of them synchronize their flashes to appear simultaneously. The females respond about two seconds later, and the males fly toward them.

That 96% efficiency was made for love.

To return to the Nature Bulletins Click Here!
Hosted by NEWTON

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Sponsered by Argonne National Labs