Fireflies have a mating problem: the lights are always on

These are tough times for fireflies. Like a lot of other insects, they face increasing threats from habitat loss, pesticides and pollution. But they also have a problem that’s unique to luminous bugs: It’s getting harder for them to reproduce because light pollution is outshining their mating signals.

Fireflies, it turns out, use their special glowing powers in courtship: Males light up to signal availability and females respond with patterned flashes to show that they’re in the mood. But bright light from billboards, streetlights and houses is interfering and blocking potential firefly couples from pairing up.

The problem can reach far from big cities: Bright light gets diffused in the atmosphere and can be reflected into the wilderness. In addition to messing with mating signals, it also disrupts the feeding patterns of the females of some species that glow to attract and eat males.

The finding was part of a study published Monday in the journal BioScience.

The study, by researchers at Tufts University and the International Union for Conservation of Nature, warned that fireflies could eventually face extinction globally because of multiple threats, including light pollution and habitat loss and habitat degradation from insecticides and chemical pollution.

Many insects are affected by habitat loss, but fireflies have it particularly bad, said Sara M. Lewis, a biology professor at Tufts and the lead researcher on the study. “Some fireflies get hit especially hard when their habitat disappears because they need special conditions to complete their life cycle,” she said.

Fireflies are a type of beetle. There are more than 2,000 species of them, found mainly in wetlands. But mangrove forests and marshes around the world are increasingly vanishing to make way for cash crops like palm oil, according to the new study.

Insects like fireflies tend to be critical to their ecosystems. Their disappearance could create havoc with food webs, especially for the birds and other animals that feed on them.

“Insects provide a lot of services,” said John Losey, a professor of entomology at Cornell University who was not involved in the firefly study. “They are predators and help us suppress pest populations, or they are pollinators and help us produce the food that we need.”

The implications are also intangible: Just about everybody loves fireflies. In a few countries, including South Korea and Mexico, they serve as ecotourism magnets.

The study was conducted by surveying experts in North and Central America, Europe and Asia. The research team found that firefly colonies faced different threats in different regions.

In Japan, for example, cultivated farmland and wetland systems called satoyama, where fireflies thrive, are disappearing as more people migrate to cities and abandon traditional agriculture. In central England, drought and flooding, exacerbated by climate change, are among the biggest threats. In Malaysia, it’s the clearing of mangrove trees.

The study did not lay out a time frame for the decline of fireflies, but Michael Reed, a biology professor at Tufts and a co-author of the study, said the insects “are being lost steadily.”

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