| Jun 04, 2009

Back to HomeOutdoors in the Land O'lakes - June 4, 2009 Lightning Bugsby Steve Blight

In another week or two, the first flashes of light start to appear in forests and fields just after sunset, signalling the start of another firefly season. Fireflies, or lightning bugs as they are called by some people, are familiar to many people. However, few are aware that these insects are actually beetles.

All fireflies belong to a family of beetles called the Lampyridae. There are about 2,000 firefly species around the world with most species living in warm, tropical environments. About 180 species are found in Canada and the U.S. All species have luminous larvae, sometimes known as “glowworms”.

Typical of many insects, fireflies have four stages to their lives – egg, larvae, pupa and adult. A few days after mating, a female lays her fertilized eggs on or just below the surface of the ground. The eggs hatch 3-4 weeks later and the larvae feed on other insect larvae, terrestrial snails and slugs until the end of the summer. Fireflies over winter as larvae by burrowing underground, while others find places on or under the bark of trees. They emerge in the spring and after several weeks of feeding they pupate for one to three weeks and transform into the flashing adults that we see.

Most fireflies in our area are mainly active in twilight, either just after sunset or before sunrise, a behaviour known as “crepuscular”. Apparently there are a number of species that are active during daylight. An animal that is active mainly during the day is technically known as diurnal, a term that accurately describes the way most humans prefer to live their lives, with the possible exception of teenagers. Most diurnal fireflies are non-luminescent, though some species that remain in shadowy areas can produce low levels of light.

Most people know how fireflies got their name, but many don't know how the insects produce their signature glow. Fireflies have dedicated light organs that are located under their abdomens. The insects take in oxygen and, inside special cells, combine it with a substance called luciferin to produce light with almost no heat.

Fireflies generally flash in patterns that are unique to each species. Each blinking pattern is a signal that helps fireflies find potential mates. As a rule, courting males are the “fancy flashers”, signalling with their light organs in characteristic, species-specific patterns of flashes. The response password from the female of the appropriate species is encoded in the time-delay between the male's flash pattern and her single flash response. When the male detects the characteristic delay-and-flash pattern of his own species, he heads for the source, and usually finds a potential mate.

However, it is not always a mate that lays waiting for the amorous male. Females from the Photuris group of fireflies are known for mimicking the mating flashes of other "lightning bugs" for the sole purpose of preying on them. Target males are attracted to what appears to be a suitable mate, and are then promptly eaten. For this reason the Photuris species are sometimes referred to as "femme fatale fireflies".

The story continues as well. Not only do these predatory females get nutrition, they also get chemical protection from some predators. The prey fireflies have chemicals called lucibufagins in their bodies, which the Photuris fireflies do not produce on their own. When the female Photuris fireflies consume the prey, they absorb these chemicals into their own bodies. Studies have shown that fireflies containing these chemicals are disliked by predators such as spiders and birds, and are more likely to be left alone.

As is often the case in nature, something seemingly as serene as a firefly flashing on a warm summer evening can have a fascinating but rather sinister side!

Please feel free to report any observations to Lorraine Julien at This email address is being protected from spambots. You need JavaScript enabled to view it.  or Steve Blight at This email address is being protected from spambots. You need JavaScript enabled to view it.

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