Some female fireflies fake a rival species' flashes to eat the males
Fireflies are beetles, more than 2,400 described species of them, and their glow probably began as a warning that the larvae taste foul. Only later did it become a courtship signal, and one genus has turned it into a trap, with females mimicking another species' flash code to lure and eat its males.
The family, Lampyridae, takes its type species from Europe's common glow-worm. These soft-bodied beetles live in temperate and tropical regions, especially marshes and damp woods rich in larval food. Every firefly glows as a larva, but only some glow as adults, and the light organ's position differs between species and even between sexes. Most are unpalatable to vertebrates thanks to steroids called lucibufagins, chemically similar to toxins found in some poisonous toads, so a glowing larva is advertising that it is not worth eating. Females of the genus Photuris have exploited the later courtship signal by imitating Photinus flash codes, drawing Photinus males in to be eaten.
The light itself is a chemical reaction in organs called photophores. An enzyme, firefly luciferase, acts on a compound called luciferin in the presence of magnesium, ATP and oxygen, the oxygen arriving through a breathing tube in the abdomen. The result is cold light with no infrared or ultraviolet, yellow, green or pale red, spanning about 510 to 670 nanometres. The Eastern American blue ghost looks bluish-white at a distance but is green up close, perhaps because of how human eyes see in dim light. The genes have been transferred into many organisms, and luciferase is used in forensics and in medicine to detect ATP or magnesium. Genome work on Aquatica leii identified two genes that build and position its lantern.
Like other beetles, fireflies go through complete metamorphosis. Eggs laid in or on soil hatch after three to four weeks; in Aquatica leii they go on water plants and the larvae drop into the water. Most larvae are specialist predators of other larvae, snails and slugs, some injecting digestive fluid through grooved jaws. The larval stage lasts weeks to two years or more, usually with a winter spent underground or under bark, followed by one to two and a half weeks as a pupa.
Adults usually survive a few summer weeks. Some hunt, some feed on pollen or nectar, and some, like the European glow-worm, have no mouth at all. The largest reach 25 millimetres, and many females never fly and resemble larvae. Japan values fireflies so highly that parks are set aside for watching them.
Source: Firefly
