Let Fireflies Brighten Your Evenings

Whether you call them fireflies or lightningbugs, seeing them in the evening is a pleasant reminder that we are moving into the early summer months. It is fascinating to watch their periodic flashes and the patterns they make with their lights. This phenomenon is called bioluminescence, which produces light without heat; this is very different from an incandescent light bulb. Some species, particularly those in western states, do not flash, or when they do, it is uncommon.

Even in Kentucky, there are a number of different species, and if you watch them carefully, each species is a bit different in how it flashes. The timing and patterns of the flashes is unique to each species. Fireflies use these unique flash patterns to recognize members of their species and identify members of the opposite sex. Studies have shown that a female firefly selects mates based on the male’s flash patterns. Higher flash rates and flash intensity are more attractive to female fireflies.

Fireflies are actually beetles, not flies or bugs, and belong to the Family Lampyridae. Adult males produce the flash near the tip of their abdomen. They use a protein called luciferin and an enzyme called luciferase to produce cold light. This is a very efficient process. Fireflies are luminescent in all their life stages, not just as adults. Larvae crawling on the ground can be observed flashing at times while they search for slugs and snails to eat.

Figure 1. Firefly adults are common in early summer (Photo: Ric Bessin, UK).

Figure 2. Firefly larvae, predators of snails and slugs, can also produce light (Photo: Ric Bessin, UK).


Females located on the ground or on other objects watch for the appropriate coded flashes of males and respond with a single flash if they spot a suitable male. Some firefly species may also synchronize their flashes—males flash as a large group followed by 5 to 10 seconds without flashes. One of the fireflies that I watch for is the big dipper firefly, Photinus pyralis. These males move upward while flashing and tracing the letter ‘J’ in the air.

Females of one genus of firefly, Photuris, may send out false flash codes to attract males of another genus. They do this to lure males of other species close enough so that they can capture and eat them. This has been referred to as the ‘femme fatale of fireflies.’ In doing so, these female fireflies harvest a defensive chemical from their unwitting meals that they use to avoid being eaten by certain spiders and birds.

Generally, during the last couple of decades, firefly numbers appear to be declining. While we may not know why this is happening or if this a just cycle in firefly populations, seeing fireflies in the evening will always remain a treat.


By Ric Bessin, Extension Entomologist



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