Firefly Nights

By Ted Watt Gazette Contributing Writer

The fireflies, twinkling among leaves, make the stars wonder.

Rabindranath Tagore (1861-1941)

What’s not to love about fireflies? Their soft, twinkling lights inspire romance and poetry. Do you remember trying to catch them when you were a kid? These warm, humid June nights are perfect for observing this unique summer spectacle. But the tiny sparkling lights in meadows, parks and backyards aren’t designed for our pleasure they’re mating signals.

Researchers have found that each species of adult firefly has its own flash pattern. Flying males signal to potential mates with a species-specific light display. Some flash only once, some emit flash trains of up to nine carefully timed pulses. Others fly in specific aerial patterns, dipping and ascending in varied paths of light. A few even shake their abdomens from side to side and look like they’re twinkling. Males and females both flash, back and forth, signaling that they are available. The next time you watch fireflies, see if you can observe the varied flashing patterns. With practice you can gauge the number of species in a given area by observing these patterns.

Entomologists classify our fireflies or lightning bugs as neither flies nor bugs, but as beetles, in the family known as Lampyridae. There are approximately 2,000 known firefly species worldwide and 123 in the United States, with more species likely to be discovered. Their bioluminescent flashes are produced in light organs located under their abdomens. The insects take in oxygen and combine it with a substance called luciferin to produce light with almost no heat.

Scientists think that most adult fireflies feed on plant nectar and live for up to several months. But in some species the adults are carnivorous, preying on other fireflies. When an unsuspecting male gives his “here I am” flash pattern, a carnivorous female answers with a flash that mimics his mate. As the hopeful male draws near, the carnivorous female grabs him and proceeds to dine. Apparently, this provides the predatory female with another benefit. Recent research suggests that these female mimics not only acquire food from their prey but also defensive chemicals (to deter predators) that they themselves do not produce in large enough quantities.

Females generally deposit their eggs in the ground where the larvae develop to adulthood. Larvae are usually predaceous, feeding on earthworms, snails and slugs. The larvae can detect a snail or slug slime trail and follow it to their prey. After locating their meal, they inject it with an anesthetic through hollow ducts in their mandibles. Then when the prey is immobilized they slowly digest its liquefied remains. Several larvae have been observed attacking a single large earthworm.

Firefly larvae are often called glowworms since they too glow with a gentle light. They have six legs and crawl slowly on the ground, somewhat resembling a flattened, miniature shrimp. They can be seen in lawns and meadows and along roadsides in spring and fall. Feel free to gently hold them and watch them glow in your hand. This glowing is probably a signal to potential predators that the larvae are toxic.

There’s a lot more to be discovered about firefly biology, and you can help. Firefly Watch, a program organized through the Museum of Science in Boston, is an online data-gathering effort using volunteer citizen scientists. It’s designed to learn about firefly populations across North America. Contributing is simple. The program is seeking information on where and when fireflies are observed in your area. You don’t have to distinguish different species. Go to www.mos.org/fireflywatch to learn how you can help with this research.

Find an evening soon, before the flashing season ends, to go out and observe fireflies in your neighborhood. You can even catch a group of fireflies in a jar and watch them glow. Just be sure to let them go before you fall asleep.

Ted Watt is an educator/naturalist at the Hitchcock Center for the Environment.

Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 525 South Pleasant St., Amherst, appears every other week. For more information, call 413-256-6006, or write to us.

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