The common sight of a small lizard clinging motionless to a wall next to a porch light leads many people to assume geckos are directly attracted to the light source. House geckos are commonly seen in urban and suburban environments, making this observation widespread. This behavior raises a question about what draws these nocturnal reptiles near human dwellings. The answer lies not in the gecko’s attraction to the light, but rather in a learned, opportunistic hunting strategy.
The Behavior: Why Geckos Gather Near Light Sources
Geckos are not drawn to the light’s photons or heat, but instead respond to the environment artificial illumination creates. This gathering is an opportunistic feeding strategy observed in many nocturnal gecko species. Geckos have learned that artificial light sources reliably concentrate their prey, making a static location a more efficient hunting ground than searching in the dark.
This behavior contrasts with true phototaxis, which is movement directly toward or away from a light source. The gecko’s presence is a secondary effect, responding to the dense food supply created by the illumination. Studies confirm that house geckos actively seek out lighted areas near human structures to maximize foraging success.
The True Attractant: Following the Food Chain
The force drawing geckos to walls and ceilings near light fixtures is the abundant population of nocturnal insects. Moths, flies, mosquitoes, and small beetles are attracted to artificial light through positive phototaxis. This insect behavior turns a porch light into a concentrated, high-density food source.
Scientists suggest that artificial light disrupts the insects’ natural navigation system, which relies on distant celestial objects, like the moon, for orientation. When an insect attempts to maintain a constant angle relative to a close, bright light, it spirals inward instead of flying straight. This results in masses of confused prey continuously circling the light source, creating a predictable buffet that geckos exploit.
Specialized Vision: How Nocturnal Geckos Hunt
The ability of nocturnal geckos to capitalize on this light-created environment is due to specialized visual adaptations. Unlike most nocturnal vertebrates that rely on rod cells for low-light vision, geckos possess specialized cone cells that function in near-darkness. These large, light-sensitive cone cells provide exceptional visual acuity at night.
The gecko eye’s sensitivity is calculated to be up to 350 times greater than the human cone-based visual system at the color vision threshold. This adaptation allows them to distinguish colors even in light levels equivalent to dim moonlight, a condition where humans are functionally colorblind. The gecko eye uses a unique multi-focal optical system, featuring distinct concentric zones of different refractive powers. This complex lens structure allows the gecko to focus sharply on objects at varying distances simultaneously, aiding in judging the distance to moving insect prey.