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Twinkle, twinkle, little bug

In many parts of the country on warm summer evenings, the sky twinkles with what appear to be flying, flashing light-emitting diodes (LEDs). The little lights are fireflies, or lightning bugs, using an interactive visual Morse code to find that special someone for a brief summer romance.

Fireflies are a large family of beetles known as Lampyridae, or lampyrids. More than 2,000 species of fireflies have been identified worldwide, but by some estimates, this is just a quarter of the total number of firefly species. All fireflies produce light at some stage during their life cycle, but not all species put on a nightly light show in search of a mate.

In addition to the "lightning bug" fireflies in which both males and females use species-specific light signals to communicate, there are "glowworm" fireflies and "dark" fireflies. Glowworm fireflies have grublike females that emerge from burrows at night and emit a continuous glow. Males seek out the glow but do not signal. Dark fireflies are generally active during the day. Instead of light signals, they use chemicals called pheromones to attract a mate.

In California, 18 species of fireflies have been identified, but the Golden State lacks lightning bug fireflies. Why Californians got the short end of the firefly stick is not clear. Predation could have played a role. The modes of communication different species of fireflies use have different advantages and disadvantages. Would-be paramours can more easily localize the source of a light signal than the source of pheromones. But light signals are more vulnerable to espionage by would-be predators because a predator must possess a chemical receptor—detector—for a specific pheromone.

Researchers have proposed that in an ancestor of fireflies, bioluminescence—light production—was used solely to deter predators and only later evolved in some species as a tool for finding a mate. The light-producing substance, luciferin, is bitter. Fireflies produce other chemicals that are distasteful and even toxic to some predators. However, other predators have no qualms about snacking on fireflies, so the types of predators in a region should influence what firefly signaling modes (and, hence, what species) are present.

Climate also influences the distribution of firefly species. The southeastern United States, with its hot, muggy summer nights, has the highest concentration of lightning bug fireflies. In California, typically cool summer nights would be disadvantageous for all but dark fireflies that are active during the day.

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