Streetlights can keep Culex mosquitoes biting into fall. What signal gets scrambled?

Answer: Short-night calendar

Short-night calendar ✓ — Correct. Many temperate insects read the season through photoperiod: the pattern of light and dark across a day. For Culex pipiens, short autumn days help start diapause, a dormant overwintering state. Artificial light at night can make the night look biologically shorter, so the mosquito's calendar says 'not winter yet.' The odd payoff is that a brighter street may delay biting shutdown without making the air feel warmer to you.

Extra breeding water — Almost, but this confuses breeding habitat with seasonal timing. Standing water controls where mosquito larvae can develop, so it matters a lot for population size after rain. The streetlight story is stranger: lab studies can change adult physiology and activity using light alone. A dry block with bright night lighting could still send the wrong seasonal cue to mosquitoes already present.

Warmer wing muscles — Not quite. Temperature affects insect activity, and warm urban nights can interact with light pollution. But the mechanism here is not simply heating the mosquito's muscles like a tiny incubator. The key cue is light timing, because day length is more reliable than a random warm afternoon. That is why very dim artificial light can matter even when it adds almost no heat.