Why flying insects gather at artificial light | Nature Communications
▻https://www.nature.com/articles/s41467-024-44785-3
Fig. 1: Insects flying around a light source in the field display 3 common behavioural motifs not seen in normal flight.
The unusual flight motifs were: a Orbiting, b Stalling, and c Inverting. (Above) Diagrammatic representations of the three behavioural motifs. (Below)_ Overlaid flight trajectories of insects performing these characteristic patterns around UV light sources. Overlaid frames are separated by aesthetically chosen fixed intervals of 52 ms (left), 20 ms (middle), and 24 ms (right) for visualization.
Abstract
Explanations of why nocturnal insects fly erratically around fires and lamps have included theories of “lunar navigation” and “escape to the light”. However, without three-dimensional flight data to test them rigorously, the cause for this odd behaviour has remained unsolved. We employed high-resolution motion capture in the laboratory and stereo-videography in the field to reconstruct the 3D kinematics of insect flights around artificial lights. Contrary to the expectation of attraction, insects do not steer directly toward the light. Instead, insects turn their dorsum toward the light, generating flight bouts perpendicular to the source. Under natural sky light, tilting the dorsum towards the brightest visual hemisphere helps maintain proper flight attitude and control. Near artificial sources, however, this highly conserved dorsal-light-response can produce continuous steering around the light and trap an insect. Our guidance model demonstrates that this dorsal tilting is sufficient to create the seemingly erratic flight paths of insects near lights and is the most plausible model for why flying insects gather at artificial lights.
Fig. 3: Motion capture of the flying insects demonstrated that the animals maintain a consistent tilt of their dorsum towards the direction of the light.
a (Left) The insect’s dorsal axis is projected onto the ground plane to compare with the light source direction. The reference axis is a global orientation reference. (Right) The direction of dorsal tilt is plotted against the direction to light. Dashed line shows a gradient of 1. Insects flying around a point source of light maintained extreme bank and pitch attitudes, as compared to animals flying under control conditions. b The relative body pitch and bank angle are plotted on a 2D distribution map. For each species, in-flight bank-pitch distribution under control conditions and near a point light source are presented on the left and right respectively.