Light show: Fireflies aplenty are making dusk magic in Ottawa

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An unusually damp summer has been good news for those who love to watch fireflies light up the dusk.

Larger-than-usual numbers of fireflies have been reported all over Ottawa this summer. These beetles use “bioluminesence” for sexual communication and signalling. Aside from their enchanting light shows, they re also important pollinators.

For nature-lovers, this summer’s flashy firefly show has been a treat.

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“Isn’t it awesome?” said Dan Brunton, a retired field ecologist who lives near Mud Lake in the city’s west end.

Brunton first noticed fireflies on his backyard for the first time about five or six years ago, but the numbers have exploded this year.

“There have been exponential observations of fireflies this year,” Brunton said. He was recently in Virginia and noted hundreds of fireflies in the fields at dusk there as well.

“I think of them as a late-summer thing. They’re a little early this year,” he said. “They seem to like hot weather. It seems to be a combination of the humidity and warmth. It’s certainly something to be enjoyed.”

Most fireflies live in wetlands and near swamps and streams, and the frequent rains this year may have given their populations as boost. The larvae — which also light up — prey on snails, earthworms and other soft-bodied invertebrates. Adult fireflies are protected by chemicals known as lucibufagins that make them unpalatable to predators. Members of some beetle families can be convincing mimics of those bad-tasting adult fireflies in their attempt to avoid predators.

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It’s unclear what species of firefly has been so prolific in Ottawa this year, with firefly bioluminescence coming in different colours depending on the species and ranging from green to amber-orange.

Brunton, for example, notes that in previous years fireflies in his backyard produced a greenish light. This year, the light has been almost orange.

“These warm, humid summer nights are great for firefly watching, and I’ve noticed lots of activity over the past couple weeks,” said Steve Marshall, a professor emeritus of environment science and director of the University of Guelph Insect Collection as well as one of the authors of the 2011 illustrated digital key on fireflies in Ontario.

“I can’t tell you, however, whether the population are any different that last year,” Marshall added.

Fireflies are more common in warm climates, but there are 23 species of fireflies in Eastern Canada, some reported as far north as James Bay, according to the digital key, which was produced by scientists at the University of Guelph and the University of Florida.

In 2011, when the digital key was published, there were nothing like it to help identify species of northeastern fireflies. The illustrated key was designed to help scientists and nature-lovers do that with photographs, notes on behaviour and maps of where each species had been reported.

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Fireflies, or Lampyridae to use the Latin name for the light-emitting family of beetles, are common in populated areas of North America. Each luminous species emits a unique repertoire of signals. Nearly all Ontario firefly species are found in the southwestern portion of the province, with most of them in broadleaf Carolinian forests.

The “Big Dipper” firefly or common eastern firefly is one of the most common firefly species in Ontario. Both the male and the female produce light, but the males can be prey to the female of another species of firefly that mimics the mating lighting pattern.

The main threats to firefly populations in North America include loss of wetlands, climate change, pesticide use and light pollution, which is believed to confuse the fireflies’ signaling, according to the Xerces Society for Invertebrate Conservation. Other sources of light such as cameras and cellphones may also confuse mating signals. It’s not a good idea to keep fireflies in jar for more than a few minutes as it keeps them from finding mates.

As of 2021, the International Union for Conservation of Nature had assessed over 128 species of North American fireflies and identified 14 as being threatened with extinction, with loss of wetlands believed to be a major factor.

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