Phototaxis

Definition

A directed locomotory response in which an organism orients its movement toward (positive phototaxis) or away from (negative phototaxis) a light source. In arthropods, phototaxis typically involves compound eyes, ocelli, or dermal photoreceptors detecting light gradients, with neural integration steering motor output. The behavior is distinguished from photokinesis, which is undirected speed or frequency change without orientation.

Etymology

Greek phōs (light) + taxis (arrangement, order)

Example

Adult moths exhibit negative phototaxis when escaping from a suddenly illuminated roost, whereas many nocturnal beetles flying to UV light traps show positive phototaxis that field entomologists exploit for sampling.

Synonyms

• phototactic response
• light-oriented taxis

Related Terms

• Taxis
• Photokinesis
• phototropism
• scototaxis
• Chemotaxis
• ocellus
• dorsal light reaction

Usage Notes

Phototaxis describes whole-body movement, not growth curvature (phototropism) or intracellular repositioning. The sign (positive/negative) is relative to the stimulus direction, not absolute light intensity—some insects switch from positive to negative phototaxis at high irradiance to avoid desiccation or predation. Spectral sensitivity varies: many Diptera respond strongly to UV, while some cockroaches avoid it. In arachnology, phototaxis is less studied but documented in cursorial spiders seeking shade.