I saw my first lighting beetles (Family Lampyridae) flashing in my backyard in southwest Ohio a little over a week ago. There were just a few; nothing to get too excited about. However, numbers have risen over the past few days to provide an impressive nighttime flashing display and I've gotten a few reports that the same is occurring in the central part of the state.
Although commonly called lightningbugs and fireflies, they are neither bugs (order Hemiptera) nor flies (order Diptera); they are beetles (order Coleoptera). There are over 2,000 species of lightning beetles worldwide and about 170 species are found in North America with most occurring east of the Mississippi. Lightning beetles are a joy of summer, delightful to look at, and fun to catch!
The beetles are usually a little over 1/2" long, elongate, and very soft-bodied. The shield-like structure behind the head (pronotum) extends forward over the head and when viewed above, the pronotum largely conceals the head. The reddish pronotum has a black spot in the center. The brownish-black wing covers (elytra) are trimmed in yellow except at the front. The lower end of the abdomen is yellowish-green and it is in these "taillight" segments where the flashing bioluminescence occurs.
Females deposit their eggs on or just below the soil surface. The resulting larvae have prominently segmented bodies and like the adults, they possess bioluminescent organs located in tiny spots on the underside of their bodies. The soft, greenish-white glow emitted from these organs gives rise to the common name of "glowworms." However, this common name is also applied to the wingless females of some lightning beetle species.
The larvae are predaceous and are particularly fond of slugs and snails, but they will also eat smaller insects and the eggs of insects and other invertebrates. The feeding habits of the adults vary with the species. Some species of lightning beetles feed on plant pollen or nectar, others don't feed at all, and females of some species prey upon the males of other species.
The glowing bioluminescent light emitted by the adults and larvae is truly one of nature's marvels. These beetles are capable of producing light without heat; the complex cascading chemical reactions that produce the bioluminescence is 100% efficient. While lightning beetles aren't the only bioluminescent organisms, they are certainly one of the best known.
The bioluminescence serves several purposes including warning defense, mate location, and for some species, food attraction. Both the adults and larvae contain chemicals the make them unappetizing to some predators; just smell your hand after handling a lightning beetle. Thus, their glowing lights are flashing the message: "you shouldn't eat me." Mate location involves Morse Code-like flashing patterns between the flying males and females of the same species that are usually found sitting on plants. The males emit a series of flashes unique to the species and females respond with their own unique flashing pattern to vector the flying males in for a nighttime rendezvous.
For some males, what happens when they complete their love flight is not what they had in their little lightning beetle minds. Females in the genus Photuris are predators and they feast on the males of other species. The femme fatale females mimic the flashing patterns used by the females of other species; they flash a "come hither" signal to lure the males to their doom. Interestingly, the ill-fated males may sometimes demonstrate a final use of their bioluminescent capability as a warning signal. Lightning beetles caught in a spider web or the clutches of a ravenous Photuris female will emit a series of close-spaced flashes that presumably translate into, "don't go towards the light!"