Why are insects attracted to light?

Gustavo Gollo

The sight of insects swarming around lamps is ancient and well known, but the reasons for this behavior remain disputed. We propose that attraction to light is not merely a sensory accident, but an adaptive strategy during nuptial flights: under certain conditions, flying toward a light source can be the optimal way to encounter mates, because it aligns flight with pheromone gradients and reproductive dispersal. We developed an agent-based model to test this hypothesis, varying inertia/slip and the acceleration produced by pheromone. The results corroborate that light-oriented flight is strongly advantageous under a broad range of conditions, reaching fixation in over 90% of replicates when slipperiness is high. In addition, the simulations reveal an abrupt transition between regimes in which non-directed flight is favored and regimes in which light-directed flight is favored. This transition is controlled by inertia/slip and pheromone acceleration and is illustrated by phase diagrams. Control simulations without the directional advantage recovered the neutral expectation of 50% blue fixation, confirming that the effect is not an artifact of the model implementation. The primary implication is ecological: if the hypothesis is correct, electric lamps exploit a reproductive strategy and disrupt nuptial flights at the stage when reproduction is most consequential. The transition adds a mechanistic dimension, showing that small changes in flight dynamics can switch populations between radically different behavioral regimes. These findings, if confirmed empirically, would reframe attraction to light as a reproductive trap and add urgency to mitigating light pollution for insect conservation.