Fireflies
It's been a great year for fireflies; they got started earlier in June than
normal this year, and they seem to have been more numerous than normal.
"Firefly" or "Lightning Bug" is the common name for nocturnal luminous insects
that are neither flies nor bugs, but beetles belonging to the family Lampyridae.
There are 23 genera and about 200 species of fireflies in North America, most of
which are about an inch or less in length. There are many more tropical and
subtropical species. In the U.S., fireflies are almost never seen west of
Kansas. Unlike most beetles which have hardened elytra (forewings), their elytra
are soft and flexible.
The adults rest on foliage during the day and fly around between dusk and
midnight. Females lay their eggs in the soil, particularly in damp places. The
larvae that hatch from the eggs are carnivorous. The larvae of some species
glow, and are called glowwoms (but so are some wingless female fireflies and the
larvae of another closely related beetle family, the Phengodidae). The larvae
overwinter in the soil, then pupate the following spring and eventually emerge
as fireflies.
Both male and female fireflies produce greenish-yellow to reddish-orange
light light from special organs on the underside of the abdomen. The
flashes are "cold light" because almost no heat is produced. The light is
created when oxygen combines with a substance called luciferin in the presence
of the enzyme luciferase, in special cells called photocytes. The rhythm and
intensity of the flashes vary with the species and probably serve to identify
males and females to each other. Synchronized flashing is characteristic of some
tropical species.
Most people are fascinated by how these insects produce light, but we should
also be aware that fireflies and their relatives are beneficial insects, in that
they help to control pests. Although the adult stage is very familiar to most
people, it's actually the larval stage which is most beneficial. The larvae are
active at night, usually on the soil surface or under vegetation, and so are
often overlooked by most people. However, many are biolumenescent and therefore
called glowworms. The larvae feed on things like snails and slugs, and also
soil-dwelling insects such as cutworms.
Here in the United States firefly larvae are primarily terrestrial, and
therefore beneficial as predators of crop and garden pests. In some tropical
parts of the world there are also species that have aquatic larvae that prey on
aquatic snails. These are thought to be important in helping control some human
parasites that use snails as an obligate host in part of their life cycle.
So, when you see fireflies flashing, remember that they're not just
interesting, but also beneficial natural enemies!
– Dan and Susan Mahr, University of Wisconsin - Madison
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