Scientist are beginning to understand that light pollution is a very significant factor in the recent rapid decline of insect populations.
According to the most comprehensive review of the scientific evidence to date, light pollution is interfering with the natural dark/light cycles of many insects. At least half of insect species are thought to be nocturnal and therefore particularly vulnerable to this kind of human-made environmental pollution.
moth flight paths around a light [Harish Abraham (CC BY 2.0) from flickr]
Moths are lured to their deaths around street lights, and garden lights spotlight insect prey for predators. The review quotes research that has shown that a third of insects trapped in the orbit of such lights die before morning, either through exhaustion or by being eaten.
Insects are important prey for many species, but light pollution can tip the balance in favour of the predator if it traps insects around lights. Spiders, bats, rats, birds, and toads have all been found feeding around artificial lights.
The danger is not confined to predation: the bioluminescent courtship signals of mating fireflies are obscured in well lit, tree-lined parks that would otherwise be perfect habitat for them. And nor is the danger confined to nocturnal insects: some fruit flies emerge from their eggs before dawn when the temperature and humidity is just right, but artificial light can interfere with this process.
fireflies [Fred Huang (CC BY-NC 2.0) from flickr]
The quality of artificial light can change the appearance of some colours: warning colours that deter predators can be obscured, as can the patterns and colours that guide parasitic wasps to their victims. Street lighting reflected from tarmac in the early evening can fool mayfly and dragonflies into laying their eggs in a car park instead of on the surface of water.
Many of the human-made environmental threats, for instance changing climate or invasive species, have natural parallels to which insects have evolved adaptations, whereas the daily cycle of light and dark has remained constant for almost all of evolutionary time. Light pollution is a relatively new danger for which many species were just not prepared.
Essentially, we are frightened of the dark. In evolutionary terms, the dark is where the predators live. The team that conducted this review found that there is even a diurnal bias to ecological research: a preference among ecologists for studying daytime rather than night-time phenomena. It’s scary out there.
We need to overcome our fear of the dark and try to lessen light pollution. Persuading our town council to reduce street lighting is one thing we might do, but turning off our outside light is a much easier thing to do that might save insect lives tonight.
moth species from the park [as attributed; from Google images]
Header picture: street lights [Thomas1313 (CC BY-SA 4.0) from flickr]
Here is another part of the environmental crisis we are creating: