Fireflies evoke a feeling of magic and wonder; elegant blobs of light dancing and blinking in the summer night.
Everything about fireflies hearkens back to a time long past. Imagine living on Earth 75 – 130 million years ago. Dinosaurs tromping and roaming. The air is hot and humid. There are no cars, no city lights, no porch lights, no stadium lights. Nothing. But it isn’t pitch black because the stars fill the sky. It will still be millions of years before humans create the first artificial light sources to change all of this. It was in these dark nights that the first ancestors of fireflies are thought to have evolved from Elateroid beetles. Yes, fireflies are beetles, not flies or bugs.
Why did flashing evolve? We think it mostly boils down to reproduction (Powell et al. 2022). In the same way that birds call to each other with song, fireflies communicate using their own love language in the form of light flashes. As far as we know, every species of firefly has its own flash pattern, a “Morse code”-like series of blinks, glows and flickers. If you can decode these patterns, you can figure out which species you’re looking at! There are an estimated 170 species of fireflies in North America. There could be several different species in your own backyard!
For those of us who grew up with fireflies as a regular occurrence, we can’t help but wonder: Where have they all gone? Like declines in other insects, there is no simple answer. Fireflies have a delicate life history that can span several years. Some species can spend as long as two years developing as larvae. During this time, larval fireflies and their prey (e.g. earthworms, snails and slugs) require clean and moist environments. They also depend on leaf litter around the yard. There is some uncertainty about if and what adults eat, but they have been observed around common milkweed (Faust and Faust, 2014).
During the adult stage, many females perch in the dark on knee- or waist-high vegetation while their male counterparts flash from the skies. Females only reveal their presence when males flash to meet their standards, effectively “swiping right.”
Heavy mowing (great than 50% of yard, every two weeks or more often), leaf litter removal, mosquito spraying with pyrethroids and fertilizer use have been associated with decreased firefly abundance (Ridenhour, 2022). Landscape practices to help maintain firefly habitat include:
- Managing your landscape to include some “wild” vegetation: patches of tall grass, common milkweed, shrubs, brush and leaf litter.
- Minimizing the use of chemical treatments in and around the borders of your property if possible. This includes essential oil treatments. Although advertised as eco-friendly alternatives, they have been linked to decreases in insect taxa, including beetles (Elias et al. 2013).
- Avoiding tick control applications from July – October. The application of any sprays to control ticks from July – October is not recommended as a cost-effective management strategy. Nymphal and adult deer ticks are the life stages responsible for transmission of most diseases. Prime season for nymphs peaks in May and declines afterward. Adult deer ticks are already difficult to find. These life stages will become increasingly more rare as we head into the summer months.
- Minimizing artificial light at night. Artificial light generated from flood lights, windows, porch lights and other sources impact the ability for fireflies to communicate with one another.
Artificial light pollution is causing our nights to grow brighter by 9.6% each year (Kyba et al. 2023). Kyba estimates that “children born today in a light-polluted area who can see about 250 stars would see skyglow quadruple by their 18th birthday – leaving only 100 stars to wish on.”
So this summer, enjoy your cookouts, pool time and beach days. But before you close your eyes, please remember to turn out the lights.
by Blake Dinius, Plymouth County (MA) Entomologist
Featured photo courtesy of David Cappaert, Bugwood.org
