The underside view of an adult firefly reveals the whitish light organs where photocytes, cells that produce light, are located. Large eyes help fireflies find the glow of mates at night. M.J. Raupp
Happy 20 years Bug of the Week
This June marks the celebration of 20 years of Bug of the Week. We want to thank all our viewers in more than 200 countries worldwide for your continued support. Last year we set a record with more than 370 thousand visits. Thank you so much. This week we call on one of Mother Nature’s most fabulous creations to help us celebrate. Three cheers for fireflies.
Much of this episode comes courtesy of Dr. Paula Shrewsbury, Entomologist at the University of Maryland, College Park, who created this great article for her “Beneficial of the Week” in the IPM Alerts - Landscape & Nursery.
“I saw my first fireflies of the season in Sharpsburg, MD on May 17th; and this week I saw fireflies flashing in Columbia, MD. It looks like it is going to be another good year for fireflies based on the amazing display of flashing lights so far.
Fireflies, also known as lightening bugs, are really neither bugs nor flies. They are characterized as soft-winged beetles in the order Coleoptera and the family Lampyridae. There are over 2,200 known species of fireflies, of which about 165 species have been reported in the U.S. and Canada. Fireflies are found in temperate and tropical regions and in the humid regions of the Americas, Asia, and Europe. In the U.S., the abundance of fireflies is greater east of the Great Plains than in western states. Interestingly, fireflies that produce light are uncommon in western North America. Some firefly species are diurnal, and therefor have no need to create light. These species are known as daytime dark fireflies and they use chemical pheromones for mate attraction. Although the adults do not light, the larvae do glow at night, similar to eastern species.
Most flashing species occur east of the Mississippi River, are about ¾” in length and are active at dusk and night. Adults and larvae of many firefly species exhibit bioluminescence – they glow in the dark! Many organisms such as bacteria, fungi, jellyfish, algae, fish, clams, snails, crustaceans, and of course insects [including some click beetles] exhibit bioluminescence. Firefly species have special light organs that make the underside of their abdomens light up.
To help celebrate twenty years of Bug of the Week, let’s enjoy one of Mother Nature’s finest light shows courtesy of fireflies. How do they produce light? See the white segments at the tip of the firefly’s abdomen. These segments contain photocytes, cells that produce light. I asked this little guy to show off his stuff. Look at him go. Don’t worry, he was released nonplused but unharmed. Male fireflies perform aerial displays to impress females watching from vegetation on the ground or on branches. If the she firefly likes the performance, she may signal back with her flash. Watch as a male firefly searches for his mate on a cluster of leaves. Eventually he finds her and their union is consummated. During June and July, take a moment at twilight to visit a lawn, meadow, or park to enjoy these beautiful and illuminating creatures.
How do fireflies make light? The light emitted by a firefly is actually a chemical reaction in the beetle’s abdomen. The light organ has special cells that contain a chemical called luciferin. An enzyme called luciferase combines oxygen with luciferin in these cells to create light. Scientists actually do not know how fireflies regulate their lights to turn them on and off. You might have also noticed how “cold” the light looks. This is because no infrared (or heat) or ultraviolet frequencies of light are emitted. Among the light-producing fireflies, lights are yellow, green, or pale red.
Firefly larvae called glow worms have luminescent organs on the underside of their abdomen. M. J. Raupp
Why do fireflies bioluminescence? The purpose of this bioluminescence varies. It is believed that the flashes are part of a signaling system for attracting mates. Both males and females emit light intermittently or in specific flash patterns. The rhythmic flash patterns produced are specific for each species of firefly and vary by sex within a species. The flashes that we see are from the males that are attempting to attract a mate. For example, males of the common eastern firefly (Photinus pyralis) flash every six seconds. Females watch the light “show” and if a display from a specific male is particularly attractive, she will flash a response but only if it is from the male of the same species. The male descends to that location to mate with her. In addition to transferring sperm to the female during copulation, the male offers a nuptial gift of rich protein, which the female uses to provision the eggs that will soon start to develop in her ovaries. Interestingly, in one species of firefly, Photuris pensylvanica, the female mimics the flash pattern of another species, Photinis pyralis, to attract the male of the other species to her. When the male of the other species arrives thinking, he has found his mate - she eats it to obtain defensive compounds used to protect her eggs. A bad surprise for that male.
Why are fireflies considered beneficials? Well, the soil active firefly larvae or glow worms are voracious predators of soft-bodied invertebrates and known to feed on slugs, snails, worms, and other soil-dwelling insects. Glow worms use their mandibles to inject prey with a paralyzing neurotoxin, making it defenseless, and then secrete digestive enzymes that liquify the prey making it easier to consume. Firefly larvae or glow-worms are believed to glow as a warning signal telling predators not to eat them as they are mildly toxic and taste nasty. It is not well known what all adult fireflies feed on but some feed on pollen and nectar and some are reported not to feed at all.
A pair of firefly larvae snack on a hapless earthworm. M. J. Raupp
Although the larvae of fireflies are referred to as glow-worms, technically this is not quite correct. Glow-worms are a type of firefly where the adult female is flightless and maintains the appearance of a larva and she emits a long-lasting glow, similar to larvae. The males have the appearance of an adult firefly. To make it more confusing, other insect larvae that glow, are sometimes called glow-worms too. Since most fireflies that produce light are in the Eastern U.S., it makes the nightly light shows we encounter here something special to behold for a few weeks during spring and early summer. Be sure to help young people you know, and others, enjoy the experience of observing and collecting fireflies. Be certain to release the little lights when you are done!”
Light pollution and fireflies
Over the past few years, many have been concerned about dwindling numbers of lightning bugs in our region. While hard data on this issue are difficult to come by, one important study conducted by scientists at the University of Virginia suggests that light pollution caused by brightly lit homes and buildings has disrupted the normal ecology and behavior of these remarkable creatures. By adding artificial light to nocturnal courting grounds, normal courtship behaviors and mating success of fireflies were compromised. The authors suggest these reductions in mating success could lead to fewer fireflies in locations with light pollution. The development of natural areas and destruction of habitat are also thought to contribute to reductions in firefly populations. Others believe that widespread use of residual insecticides to treat lawns may have contributed to the lightning bug’s decline. Perhaps unfavorable weather cycles or a dearth of food for predatory lightning bug larvae, which live on the ground, may have suppressed their numbers in years past.
What can be done to help our fireflies and other nocturnal insects? Reducing sources of artificial light at night (ALAN) by using motion detectors to trigger security lights, timers and dimmers to regulate intensity and timing of illumination and simply turning off unnecessary lights can help. Outdoor lighting along pathways can be shielded from above to reduce light scattering that might attract flying insects. To learn more about light pollution and some solutions to ALAN, visit DarkSky.
During these glorious days of June and July, take a moment at twilight to visit a lawn, meadow, or park to enjoy these beautiful and illuminating creatures.
Acknowledgement
Bug of the Week thanks all our viewers over the last two decades. Our F2s, Eloise, Abby, and Jackie provided the inspiration for this episode and Dr. Shrewsbury provided much of the cool content. The interesting articles “Experimental tests of light-pollution: Impacts on nocturnal insect courtship and dispersal” by Drs. Aerial Firebaugh and Kyle Haynes, “Flash Signal Evolution, Mate Choice, and Predation in Fireflies” by Sara M. Lewis and Christopher K. Cratsley, “Silent Earth” by David Goulson, and fascinating studies of Dr. Sara Lewis and Dr. Thomas Eisner and their colleagues, served as resources for this Bug of the Week.