For Melanophila beetles, forest fires aren’t just hot. They’re hot.
As flames start ripping through forests, as they often do in the late summer, most animals flee or take refuge for obvious reasons: They don’t want to die. But Melanophila beetles flock to the flames and start looking for sex. While the wood is still smoldering, they find a mate and copulate in the heat of the moment.
Black and roughly thumbnail-sized, Melanophila are among a small number of species around the world known as fire, or pyrophilous, beetles. They are attracted to flames and depend on fire for their reproduction. After breeding among the embers, the insects lay their eggs in freshly scorched bark. Those eggs then hatch into wormlike larvae that feast on the recently burned wood.
Deliberately putting oneself in a forest fire to reproduce may seem like an awful idea, but it comes with a number of advantages. There are few competitors and plenty of food for their bark-biting offspring, for example. That’s likely why this behavior evolved.
Adaptations like this will come in handy as the world continues to warm, making wildfires more widespread and severe. These beetles remind us that climate change won’t just be a dead end for animals; some species may thrive in a world ravaged by fire.
How fire beetles find flames
What’s most remarkable about these beetles is how they find wildfires in the first place. Like home security systems and night-vision goggles, the small body of a fire beetle has built-in infrared sensors. These sensors — known as sensory pit organs — detect infrared radiation, which is a proxy for heat. Located on the insects’ underside, those pits point them in the direction of a fire.
Research also suggests that fire beetles may be able to detect smoke using sensors found in their antennae. One particularly entertaining anecdote supports this idea: During football games at the University of California Berkeley, back in the 1940s, some 20,000 cigarettes would be lit at one time, according to the book Fire Ecology of Pacific Northwest Forests. “A haze of tobacco smoke would hang over Memorial Stadium,” author James Agee wrote. Attracted to the smoke (or perhaps the warmth of the burning tobacco) a swarm of Melanophila beetles would swarm the stands, angering fans.
These sensory systems help beetles detect wildfires from truly impressive distances. One study in 2012, based on modeling, suggests that they can become “aware” of large fires from roughly 80 miles away, or about the distance between New York City and Philadelphia, as the crow flies. And so often where there is fire, there are fire beetles — a fact firefighters know all too well.
“Wildland firefighters hate these beetles,” said Lynn Kimsey, an entomologist at the University of California Davis and director of the Bohart Museum of Entomology. “When you’re in working on a fire line, especially around trees that are burning, the beetles will come in, in big numbers, and they’ll get into your turnouts and bite.”
The bites can feel a bit like a bee sting, and sometimes firefighters will wear bee veils to protect themselves.
For the past few days covering the River Fire, these bugs have been plaguing @anthonyjguevara, @DwelleKMPH and me. They have a vicious bite and they gather near the fire in swarms - as though flames, ash, and smoke weren't enough to deal with. We asked firefighters about them... pic.twitter.com/IjDX5MUIbW— Marie Edinger FOX 35 (@MarieEdinger) July 16, 2021
Why these beetles seek out scorched Earth
When male beetles arrive at a forest fire, they have one thing on their mind: sex. They often perch on a tree “close to burning or glowing wood or hot ashes,” researchers explain, and when they find a female, “they try to copulate vigorously.” Then the females lay eggs under the bark of burnt trees.
The simplest reason why they do this is that their offspring, the beetle larvae, can only persist on the wood of burned trees. This makes some sense: When a tree has been scorched by flame, it has a weak or nonexistent defense system, allowing the beetles to easily bore through the wood under the bark. “The beetles can get in there and feed freely,” Kimsey said.
Fire beetles likely lay their eggs in forest fires for a few other reasons as well. Most insects tend to avoid recently burned areas, so the beetle larvae have fewer competitors — they have a wood buffet all to themselves. These regions also typically have fewer predators, such as birds. (Although, in a remarkable example of evolution, some species, like the black-backed woodpecker, have evolved to eat fire-associated insect larvae.)
There’s also some evidence that beetle larvae develop faster in these environments because heat speeds up growth. That means beetles produce more babies in less time.
A rare climate change winner?
Rising temperatures linked to climate change are already a problem for many ecosystems and species. They’re fueling coral-killing heat waves, causing birds to shrink, and generally making much of the planet less suitable for life.
At least in the short term, fire beetles may defy these negative trends. Climate change is likely to make wildfires more widespread and extreme, and scientists suspect these beetles can only breed with fire.
For now, this is just speculation, Kimsey said. “We have no idea what they’re doing when there isn’t a fire,” she said. But it’s clear that climate change will produce not only losers but some winners — and these beetles may be one of them. Indeed, a world on fire may be a world full of horny beetles.