Flashing Light May Guide a Firefly to Mate, but Scent "Seals the Deal"

Fireflies light up the night to attract mates, but attraction may not be about being flashy; it could also be about who smells the best. 

New research published in BMC Genomics looks at the genetics of the common eastern firefly (Photinus pyralis) and found that besides bioluminescent flashes, fireflies may also be using pheromones to attract mates. 

"Fireflies have always been seen as a visual species. They light up, and we assume that's how they talk to each other," said lead study author Sarah Lower — who helped map the firefly genome in 2018 — in a press release. "But we looked at genes for odorant receptors — the ones tied to smell — and found there's a lot more going on than we thought."

According to the study, the research team collected 102 odorant receptor (OR) genes. Many of which were expressed strongly in the antennae. Surprisingly, there was one OR gene that presented itself more in males than females, indicating that this could be used for attracting mates. 

"That caught our attention," Lower said in the press release. "It's the only odorant receptor gene that was turned on more in males than in females. In adult males, the primary goal is to find a female to mate with. This gene might help them do that through close-range chemical signals."

It’s been a long-held belief that fireflies relied on visuals to find mates; however, these results may challenge this belief. 

"We were not expecting to see this in P. pyralis, which is one of the most common firefly species in North America," Lower said in the press release. "This suggests that even in these species with flashing adults, smell may be part of a two-step system — light to get close, then scent to seal the deal."

Read More: Are We Really the Last Generation to Enjoy Twinkling Fireflies in the Summer?

For the study, to collect firefly pheromones, the research team did what many of us have done as children: collect eastern fireflies and put them in a jar. 

“This is a very special jar,” Lower says. “It's attached to an air pump so air is continually circulating to this jar, and on one end, the air comes out of the pump, goes into the jar, and it passes through a charcoal filter[…].So, this is cleaning the air. Then the air mingles with the firefly in the jar and gets sucked out the outtake, and then in the outtake we have another one of those charcoal filters, but this time, it's collecting all the smells that are coming off the firefly.”

After collecting the pheromones, the research team used RNA sequencing to compare the gene expression in male and female firefly antennae. The team found that the OR gene PpyrOR6 — a male expression — stood out the most. 

"This could help the male locate a female or even avoid predators," Lower said in the press release. "Some female-mimicking species lure in unsuspecting males and eat them — the so-called femme fatale fireflies. Smell might be part of how males navigate that risk."

Fireflies are currently facing numerous obstacles when it comes to mating. Certain firefly species are seeing massive drops in numbers. This can be linked to climate change, pesticide use, and light pollution. The common eastern firefly species is doing better than most, however, and their pheromones may have something to do with it. 

"Smell is a much harder modality to disrupt," Lower said in the press release. "Light pollution is everywhere, and it affects both people and animals. But olfactory signals may stay clearer, which is another reason this discovery is so interesting."

Eastern common fireflies may not be the only species to possibly use pheromones to attract mates. Winter fireflies, also known as dark fireflies or unlighted fireflies, come out during the day and don’t use light to attract mates. Lower thinks that pheromone receptors are helping them find potential partners. 

Lower says she hopes that this pheromone research could one day help with firefly conservation, particularly as a way to collect population data. 

“It would be really great to see folks be able to use something like this for monitoring populations,” Lower says. This is especially important because researchers know that lighted firefly populations are declining; is the same true for dark fireflies?

Read More: How Fireflies Glow — And What Their Signals Mean

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

• BMC Genomics. Antennal RNAseq reveals odorant receptors with sex-biased expression in the common eastern firefly, Photinus pyralis

A graduate of UW-Whitewater, Monica wrote for several organizations, including one that focused on bees and the natural world, before coming to Discover Magazine. Her current work also appears on her travel blog and Common State Magazine. Her love of science came from watching PBS shows as a kid with her mom and spending too much time bingeing Doctor Who.