The Fate of Fireflies
Warm summer nights have a way of thawing out memories: a night out, a dusk walk with the dog, a simple walk up a rural driveway. Whatever the scene, many of them are accented with fleeting blooms of lemon-lime light: fireflies.
Firefly populations vary from year to year depending on the conditions in their habitats – grassy fields, forests and stream and river banks. Their food sources are abundant in the “lush.” Firefly larvae and juveniles tend to eat slugs, snails and earthworms until they mature; the winged adults snack on nectar and pollen. In short, fireflies need moisture to survive.
While firm data is hard to come by, fireflies are becoming less common, according to PJ Liesch, the “Wisconsin Bug Guy” who runs the UW Insect Diagnostic Lab at UW-Madison, but the rainy spring and summer bodes well for short-term populations. “When I look at the weather this year, with all the rain we’ve had, these are some conditions that could be very good for fireflies,” said Liesch. “At least in the immediate future.”
It’s time to pick your Milwaukee favorites for the year!
Although this sounds promising, human activity threatens fireflies via habitat destruction, pesticides and artificial light. Liesch says fireflies have “very limited dispersal.” Some fireflies spend their entire life within a few feet of where their egg hatched. This intense localization means that if their habitat is destroyed, the flies don’t just move along, they die out.
Their signature lights are a mating ritual. Male fireflies flash to female fireflies and the females reciprocate by flashing back. Artificial light at night disrupts this delicate dance, complicating fireflies’s ability to communicate and locate each other.
Fireflies can be directly or indirectly affected by pesticides and other lawn chemicals. Mosquito insecticide will kill fireflies that land on treated plants and bushes. And if a weed control application also kills slugs and earthworms, it will indirectly kill fireflies.
“Where there’s smoke, there’s fire, so there’s certainly very valid concerns related to firefly populations on a global basis,” said Liesch.
Firefly Fun Fact
From 1940 to the late nineties there was firefly commercialization. Chemical companies would pay for people to send in large collections of fireflies. The fireflies would then have their light-emitting chemical compound, luciferin, harvested to help determine the quality of certain metals used to produce light. Modern science now has a way to produce these chemical compounds artificially.
Firefly Fieldwork
Fireflies are a type of beetle with over 2,000 variations; of the 132 species assessed by the International Union for the Conservation of Nature (ICUN), at least 18 species in the United States are endangered. But the many variants – some don’t light up, some have markedly different lighting and flight behavior, some have big differences between sexes of the same species – make them difficult to study.
“That was a big stumbling block for firefly conservation,” said Candace Fallon, a senior conservation biologist with the Xerces Society for Invertebrate Conservation. “It’s very difficult to monitor fireflies and at this point, we are so early in the game that we are still working to figure out where fireflies of different species occur, let alone how many are in those populations.”
Because of this obstacle, ICUN has no population data; instead, species are scored based on geographic range, habitat loss, associations and threats. To determine the extinction risk, ICUN Redlist used literature reviews, talked with firefly researchers and compiled data from online repositories.
ICUN provides a “menu of options” to help researchers study fireflies, Fallon said. Time-lapse photography and videography have proven useful, Fallon says, as tracking an individual firefly can be hard at night to the naked eye. For example, an individual can claim to see one firefly flash five times while someone standing nearby sees five separate fireflies.
“The fact that we are just starting to get these numbers is unfortunate because if they have been declining, there’s nothing capturing that besides data like habitat loss,” said Fallon. That research is just beginning. According to ICUN’s Redlist, of the 42 firefly species recorded globally, 19 have declining populations, two are stable and the rest are unknown.
Candace Fallon’s Firefly Preservation Protocol:
- Be aware of light pollution. Turn off outdoor lights at night, especially during the summer. If there are safety concerns regarding turning off lights, install a dim red light or motion detectors/timers. Close curtains to keep indoor light from spilling outside.
- Leave your yard a little messy. Fireflies are wildlife, so they need flourishing bushes and grass to sleep, shelter and hunt. Firefly larvae eat the most food – snails, slugs and worms – so even if we aren’t seeing the flashing adult, there are still many developing in the “lush” on the ground all year long.
- Limit insecticides. Broad-spectrum or beetle insecticides can wipe out fireflies. Be mindful and avoid the cosmetic use of pesticides, such as herbicides.
