Common eastern firefly

Description

Photinus pyralis, known by the common names common eastern firefly and big dipper firefly, is the most common species of firefly in North America. P. pyralis is a flying and light-producing beetle with a light organ on the ventral side of its abdomen. This organism is sometimes incorrectly classified as Photuris pyralis, which likely results from mistaking the similar-sounding genus Photuris. The Photuris female may also lure a Photinus pyralis to be eaten to obtain spider-repellent steroids called "lucibufagins". In males the light organ covers the entire ventral surface of the three most posterior segments and in females it only covers a portion of the third posterior segment. These fireflies are most noticeable around twilight, in the early part of the evening and hover close to the ground. The species' common name refers to the characteristic flight of the male, which flies in a J-shaped trajectory, lighting on the upswing. During flight, the J-shaped flight pattern is used in combination with patrolling flash patterns while seeking a mate. Their flashes are stimulated by light conditions, not by rhythmic impulses as originally thought. The genome of Photinus pyralis was sequenced in 2018. Males of Photinus pyralis locate females by a series of light flashes, to which females respond with a coded delay flash. The light organ of P. pyralis is composed of two layers; a layer of refractile cells on the dorsal side and a photic layer with light-producing cells on the ventral side. The light organ (specifically the photogenic layer) is supplied with numerous tracheal branches, which are thought to provide the required oxygen for light production. The light-producing enzyme is luciferase, and is found within cells of the lantern. Luciferases require oxygen, luciferin and adenosine triphosphate (ATP) to catalyze a chemical reaction that produces bioluminescence in these insects. It has been shown that the glow is not controlled by the tracheal end cells (which were thought to contain valves) nor by central nerve impulses through studies involving low oxygen conditions. Pupae of these beetles have different light organs than the adult. They do not have the characteristic tracheal end cells of the flashing adults, and whereas the adults emit bright flashes, pupae emit low intensity glowing.