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#57: Fireflies

Litinsects #57: Fireflies

© Radim Schreiber

You may know them as fireflies, lightning bugs, or glowworms depending on where you grew up…  these glowing bugs are actually neither flies, nor bugs, nor worms but beetles. They are a special group known for their BIOLUMINESCENCE. So how does that work?

Bioluminescence is light produced by an organism through a chemical reaction. In some animals light is produced by bacterial symbionts, in others the light is produced by the organisms themselves, as is the case with fireflies. (Side note: this is different than biofluorescence, which is the absorption and re-emission of certain wavelengths but it doesn’t involve a chemical reaction.)

Fireflies have a LIGHT ORGAN in their lower abdomen in which a special reaction takes place; it produces light but no heat (thus often called “cold light”). A compound called LUCIFERIN, coming from the Latin word for „light-bearing“ (also the same etymology for the name Lucifer) is contained in these light organs. Light is produced when luciferin combines with oxygen, calcium, and ATP (a molecule that provides energy in cells) in the presence of an enzyme called luciferase. The resulting light may range from yellow to green and even to pale reddish.

-Each firefly species has its OWN PATTERN of light flashes to attract mates. In most species both sexes glow although sometimes only one sex does. Usually males flash to advertise themselves to females, who respond with flashes to show their location. The females of certain species use this to their advantage by mimicking the flash signals of another species’ females to attract males to prey upon!

-Some species have LARVIFORM FEMALES, which are wingless adult females that closely resemble larvae in appearance. These females stay on the ground while males fly around flashing

-Though it seems counter-intuitive there are in fact fireflies that are not bioluminescent and some that flash but are active during the day. These species usually rely more on PHEROMONES to attract mates (more on those to come soon!)

-Flashing can even deter predators! Some fireflies produce defensive steroids that make them taste very bad, so predators learn to associate the flashing with a bad-tasting meal and leave them alone

-Fireflies are very sensitive to artificial light, since they depend on their light signals to reproduce. They are therefore good BIOINDICATORS of light pollution

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