Friday, June 27, 2014


A firefly about to start its nightly light show

     This is the time of year that nature puts on one of its light shows. The Fireflies or Lightning Bugs are visible for a little over a month each year, displaying to each other to attract their mates. They are neither flies nor bugs, being actually beetles in the family Lampyridae capable of bioluminescence to produce cold light. There are about 2,250 species worldwide on every continent except Antarctica. North America has about 127 species (although they're rare west of Kansas) with the DC area having over 3 dozen kinds.
     Although not all adult fireflies actually glow, all species have eggs, larvae, and pupae that light up. This ability is thought to serve another role besides calling to mates in that they may signal to potential predators how distasteful they are. Some are even toxic enough to kill the animal that eats it. This is why bats do not catch them and why they are so easy for even people to capture. Most animals just leave them alone. Those that get caught in webs or are accidentally squished often flash dramatically or just keep their light on, perhaps as one last attempt to warn the attacker they are toxic. 
     Firefly larvae are called Glowworms and are all predatory. They feed on soft-bodied creatures such as earthworms, slugs, and snails, sometimes eating prey much larger than themselves. Most take 2 years to reach maturity and metamorphose into adults.
     In general in our area, the adult males fly while they give species-specific light signals to the females who remain on the ground. Each species has their own pattern, number of flashes, duration, color, habitat, season, and time of night they signal. Females are very picky in choosing the one male they will mate with.

The light organs on a male firefly, females have smaller organs and eyes.

     The most common species locally, indeed in all of North America, is the Eastern or Big Dipper Firefly (Photinus pyralis), the state insect of Tennessee. It gets its common name because the males use a signal that dips, almost in an upwards forming "J" shape. A neat naturalist trick is to call them in by mimicking a female of the species using a penlight. The trick is to flash a response back to them from ground level 2 seconds after they flash and hold it for a 1/2 second. The males will often respond if they're within 15' or so. Keep calling back to them but point your penlight down as any approach so it is not too bright. You will be amazed at how close you can get them to come sometimes.
     Whether you choose to call them in or catch them in a jar, do not hold them for long. Their adult lives only last about 2 weeks and they dehydrate quite quickly. Make sure to have a moist piece of  paper in their jar if you intend to contain them for any extended period of time, say overnight.
     Keeping your lights off to reduce "light pollution," not mowing your lawn right before dark, and not using pesticides/herbicides to treat your lawn, you can ensure there will be these natural light shows for generations to come.

A firefly has found the light of its life and they are mating.

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