Fireflies

Have you ever seen the blink of light made by fireflies in a backyard or park on a summer evening? Have you ever tried to catch fireflies in a jar to make an insect-powered light? What are fireflies and what are they doing? Where can you find them? How can you attract them to where you live? This page will help you answer a few of these questions, and maybe come up with more questions.


First of all, fireflies are not flies at all. Most are beetles in a family called Lampyridae. Flies have only one pair of wings. Other insects that have wings have two pairs of wings. When an insect's common name ends with fly, as in dragonfly or stonefly, it usually is not a fly at all. If its name has fly as a separate word, like house fly or fruit fly, it usually is a real fly. Fireflies are also sometimes called lightning bugs or glowworms. Common names can be confusing. That is why most scientists eventually use scientific names.

Where to look:

First, North American fireflies are mainly found east of the Rocky Mountains. Parks and older neighborhoods where most of the yards are not sprayed with pesticides are the best places to look. Why no pesticides? Not only can spraying kill the beetles themselves, but firefly larvae are predators which eat earthworms, slugs and snails. If sprays are used, they may kill the creatures needed by the larvae for food as well as poison the larvae.

Some tall grasses or garden plants nearby will give the beetles a place to hide during the day. The best firefly light displays I ever saw were along the Brandywine River in Chadds Ford, Pennsylvania where lots of tall grasses and wildflowers grew near the river. At night, the flashing fireflies were spectacular. Maybe there is a river or stream which runs through a park or through the countryside near you where you could go for a drive with grownups to look for fireflies this summer.

Some people think that too much outdoor lighting may make it hard for fireflies to find each other and mate. So try to look in areas where there is still some natural darkness.

When to look:

July is often the best month in the northeastern United States to look for flashing adults, but some can be found as early as June or as late as September. Just after dark is the best time. As the night gets later and cooler, some fireflies may stop flashing.

Larvae may be found on the ground among the grass and leaves in the same kinds of areas as the adults. Not every kind of adult beetle in the family Lampyridae can make light. But the larvae, sometimes called glowworms, and the eggs of every member of this family do glow.

What to look for:

Adults that flash are searching for a mate so that eggs will be laid for fireflies to continue to be around. Scientists have found that different kinds of fireflies have different flash patterns and flash from different heights above the ground. One kind might give a long flash followed by a couple of short flashes. Another might give a series of short flashes. Some flash as they fly upwards and then drop towards the ground before flashing again. Some kinds have a different flash made by the males than by the females. How many different patterns can you find?

You might want to gently catch a firefly and look to see what part of it flashes. Can you find any worm-like larvae glowing as they crawl on the ground? Do they flash or just glow? What parts of them make light?

Some observers have reported whole trees of fireflies flashing together. For a long time this was thought to happen rarely and by chance but there have been good reports in recent years of this happening in areas of the southeastern United States.

To learn more:

National Geographic has an informative website about fireflies.

The Firefly website also provides great information and pictures on these fascinating insects.

Go to the library and look for books and poems that mention fireflies. These strange and wonderful insects have inspired people ever since they were first noticed.

Think of questions you have about fireflies. Think of ways to answer your questions. Investigate!

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