Insects hovering around the lights on your porch won't be attracted to the light. Conversely, data from high-speed infrared cameras suggests that they may have forgotten which way is up.
Moths and other insects naturally turn their backs to the light. However, researchers reported in Nature Communications on January 30 that when insects turn their backs on artificial light sources, their sense of direction appears to be reversed. Insects may lose track of their position on the ground, causing them to fly in circles or dive towards the ground.
Florian Altermatt, an evolutionary biologist at the University of Zurich who was not involved in the study, said the findings were the first "satisfactory answer" to the long-standing phenomenon of how moths and other insects flock to streetlights and flames. "Interestingly, this is actually a fairly simple explanation, contrary to the more complex explanations that preceded it. ”
These hypotheses include flying insects being blinded by light and trapped, and insects interpreting light sources as places to flee quickly. Another view is that the moon's light is a compass, and nocturnal insects mistakenly use artificial light to navigate the world. These lights can be lethal to insects.
Just as pilots flying airplanes have a myriad of tools to calculate the direction of up when they gain speed, flying insects may turn their backs to the light from the sky, keeping their feet pointing towards the ground. Samuel Fabian, an entomologist at Imperial College London, said: "It was a very good idea until someone invented LEDs, but at this point, it's a very bad idea. ”
Fabian and his colleagues use high-speed infrared cameras to track how artificial light affects the flight of various insects. At a field observatory in Costa Rica, the team observed 10 orders of wild insects, including moths and flies, circling endlessly around hanging or standing lights. Others fly upwards on steep climbs, losing speed until they can no longer fly higher. When the light source pointed upwards, some people rolled over and walked towards the ground.
During the flight, even if the insects eventually crash, they will keep their backs lit at all times. The same goes for moths and dragonflies observed in the laboratory.
Yash Sondhi, an evolutionary biologist at the McGuire Lepidoptera and Biodiversity Center at the Florida Museum of Natural History, said the results "don't fit any of the theories that have been put forward before." If this symbolizes an escape route, these insects will not fly towards the light like they do. They also don't fly in a smooth spiral, which suggests that the light acts as a compass.
Instead, "it's a bit like someone grabbing (the pilot's) joystick and pulling it in the wrong direction," Fabian said.
Normal flight is restored when the position of an artificial light resembling the sky is opposite the ground. Crash landings are common when teams light up the white sheets on the floor. But when a white sheet reached into the canopy above the floor, bathed in diffused light like the sky, the insect flew over and was not trapped by the light.
In the lab, there are some exceptions. Drosophila species – which can fly in the dark – is not strongly affected by light. The coriander hawk moth (Daphnia) can also fly under ultraviolet light or LED lights without deviating from course. However, in the wild, moths can still be culled. The reason for this, Sondhi says, is unclear, but one possibility is that insects may sometimes suppress their response to light. Or it could be something that the individual learns over time.
Brett Seymour, an animal and visual ecologist at the University of Texas at El Paso, who was not involved in the study, said that while it's clear that artificial light would get insects into a crash course, more research is needed to confirm whether this will happen because insects use skylight to navigate regardless of whether artificial light is present.
Seymour, Sondhi and other scientists are also collaborating to explore other unanswered questions about the effects of light pollution on insects, such as how vulnerable insects at different latitudes may be.
Another question Seymour and colleagues are exploring is whether installing fixtures on the lights so that insects don't see much light would make streetlights less attractive to insects flying. "Now that we have a mechanism for how moths fly to these lights, we can now better design the fixtures so that they don't actually behave this way," Seymour said. ”。