Fireflies

Nature Watch
July 23, 2008

By Susan Benson,
CNHM Director of Education

Most anyone who is asked would be able to share a memory of firefly experiences throughout their childhood. The topic has come up several times this past two weeks with Museum visitors, shortly after I observed my first fireflies for the summer season. Sometimes called lightning bugs, fireflies are neither flies nor bugs, but are beetles, the most numerous order of all insects. About 130 different species of firefly illuminate summer nights around the globe.

The telltale flash you see on a summer evening is made by male fireflies flashing patterns of light to attract females, who signal in response from perches in or near the ground. When the male sees the female’s flash he continues to signal and moves closer. Eventually, through a series of flashes, they find each other and mate. Although other insects can produce light, fireflies are the only insects that can flash their light on and off in distinct signals.

Each species of firefly sends different mating signals. For example, the male firefly of the species Photinus pyralis beams a single half-flash while flying upward. To our eyes, the flash looks like the letter “J” spelled out in the night air. The female responds with a single flash.

Another species, Photinus consumilis, signals his mate with a rapid succession of flashes. She responds with two beams. In general, males will not fly down to a female that sends the wrong species signal. However, some females of differing species have evolved the ability to mimic the response flashes of species other than their own. As the male flies down to a mimicking female, he may be captured and eaten.

Here’s a fun way to learn about local fireflies. Go outside at different times during the evening and watch for their twinkling signal. Gently catch the fireflies in a jar. Make sure that air is provided by punching holes in the container lid. Observe the flashing pattern, counting the number of flashes and recording how long they last and the time between flashes. Record your data for five minutes.

Next, return to your capture site and release the insects. Wait one hour and return to your site. Recapture fireflies and repeat your observations. If you notice a different flashing sequence, you probably have a different species. Happy firefly hunting!

Nature Watch is brought to you by the Cable Natural History Museum. For 40 years, the Museum has served as a guide and mentor to generations of visitors and residents interested in learning to better appreciate and care for the extraordinary natural resources of the region. The Museum invites you to visit its facility in Cable at 43570 Kavanaugh Street or on the web at www.cablemuseum.org to learn more about exhibits and programs.