There is something magical about fireflies. On warm and humid summer evenings, the flashing lights in fields, meadows and even some backyards are a quintessential component of early summer. Fireflies appear in all sorts of movies and stories, including a book that I just read over the weekend celebrating the fourth. I suppose it is possible that there are people who have never seen the light display on summer nights, but I am quite sure that there are many people who have never actually seen the insect responsible for the enchanting shows. Looking through my records, I am absolutely astounded that I haven’t done a column on fireflies before, so here we go.

Fireflies, also know as “lightning bugs,” are actually not flies at all. Instead, they are a group of small, soft-bodied beetles that have been lighting up the landscape on warm nights since the late Cretaceous Period, which culminated in the extinction of the dinosaurs. Somehow, these insects made it through that catastrophe and they have evolved into an entire family of beetles (the Lampyridae) that contains more than 2,400 species worldwide.

Common in both the temperate and tropical zones of the Earth, these bugs show tremendous diversity and have been further divided into a large number of genera and species. In our area, it is highly likely that the specific insect that we see at twilight is the Pennsylvania firefly (Photuris pensylvanica).

The Pennsylvania firefly is a species that spends most of its life span underground as a larva. They spend up to two full years in the decaying leaf litter of grassy areas where, believe it or not, they are voracious predators. They move around in this murky environment and search for snails, slugs and worms that will be consumed. To achieve this, the larvae can inject powerful poisons into their soft-bodied prey. These poisons immobilize their victims, allowing the larvae to eat the small animals that might otherwise flee, or put up a fight.

After spending two years patrolling the undergrowth, the firefly larvae will create a small chamber underground where they begin their transformation to adult beetles. Known as “pupation,” this is a well-known stage in the life cycle of butterflies (especially Monarch Butterflies). The interesting thing to understand is the fact that all insects undergo this transformation. While “pupating” the tissues and organs of the insect are slowly transformed. Wings develop and the appendages required for life in the air (including antennae) appear. This process begins in late April and takes about three weeks, during which the insect (unable to eat) lives on fat reserves.

In very late May, and in early June, the adults emerge and begin the reproductive portion of their life cycle. They must complete the mating process in about 60 days, before the adults die off in what appears to be programmed death. The adult beetles are themselves voracious predators of insects and invertebrates, and the females of the Pennsylvania Firefly have earned themselves the moniker “femme fatale”. This is because they will imitate the flashing pattern of other species of fireflies to lure in hopeful males that are captured and then consumed.

The normal flashing pattern of the male Pennsylvania firefly is a short flicker of light followed by a longer, sustained glow. This is usually referred to as a “dot-dash” display. Males will fly over promising habitats — wet, grassy areas with tall grasses and lots of damp, decaying vegetation — and they will flash continuously for hours. The females remain on the ground, or at least near it, and they scan the airspace above them for a particular display that they like. They respond with various flashing patterns that let the males know where they are. The males then drop down to Earth where mating will occur.

Once mated, the females will lay up to 100 spherical eggs (which are also bioluminescent) in areas that contain moist soil and lots of decomposing plant matter. About one month after being laid, the eggs hatch and the predatory larvae emerge. Sadly, there is a vulnerability in this life cycle that is unfortunately impacted in a very negative way by humans. We tend to keep our grassy areas cut short, rather than letting them grow tall. Short grass does not offer as much protection from the sun, and the ground can dry out as a result. The addition of herbicides and pesticides to lawns can also have a devastating impact on fireflies. Finally, urban areas may suffer from light pollution at night, which makes the signaling between males and females much more difficult. As a result, many places may be devoid of fireflies at night.

Today’s composite photo shows two views of a male Pennsylvania firefly. On the left you see the dorsal view, which shows the wing covers (or “elytrons”) with their distinctive yellow longitudinal stripes. Just below the head is another part of the shell (the “pronotum”) with its distinctive “eye” coloration. You can imagine the rusty-orange iris complete with a black “pupil” spot. All of this is surrounded by a light yellow “sclera.” On the right, you see the same insect lying on its back. Now you can see the light-emitting organ at the end of the abdomen. You can also see the huge eyes that the beetle needs in order to spot the flashing of an interested female.

The fireflies won’t be out much longer, so make sure that you find yourself a dark hayfield where you can watch the quiet wonder that is produced by these wondrous creatures. I happen to be very lucky in this regard because I live in a quiet, rural area with lots of long grass and no light pollution. On an ideal evening I can see dozens, even hundreds of fireflies blinking in the late evening and early nighttime. It is a scene that is truly wondrous to behold.

Bill Danielson has been a professional writer and nature photographer for 28 years. He has worked for the National Park Service, the US Forest Service, the Nature Conservancy and the Massachusetts State Parks and he currently teaches high school biology and physics. For more information visit www.speakingofnature.com, Speaking of Nature on Facebook, or the Speaking of Nature Podcast.