What the Actual Data Shows
Aedes aegypti, the tiger mosquito that is responsible for most residential biting in Austin, becomes active when nighttime temperatures consistently remain above fifty degrees Fahrenheit. In Austin, this typically occurs in late February or early March in most years. By April, populations have begun rebuilding in earnest.
The eggs that tiger mosquitoes lay are drought-resistant. They can remain viable in dry containers and leaf litter through the winter and hatch as soon as water and warmth return in spring. The first generation of adults emerges from these overwintered eggs, often before homeowners are thinking about mosquito season at all.
Why Starting Late Has a Cost
CO₂ trapping works by population suppression over time. A trap started in late March, when the first-generation population is small and has not yet reproduced, builds suppression efficiently. A trap started in late May or June, when the population has gone through two or three reproductive cycles, faces a much larger baseline population and takes longer to achieve the same level of control.
This is not unique to CO₂ trapping. Any population management approach is more effective at low population levels than high ones. The practical implication is that the season’s control quality is largely determined by when you start, not just by what you use.
The Fall Extension
Austin’s mosquito season extends significantly later in the year than most residents expect. The combination of warm fall temperatures, post-summer rain events, and the urban heat island in central Austin neighborhoods can keep mosquito populations active into November and December in warmer years.
The practical implication is that the appropriate end of season is not Labor Day or the first cool week. It is when nighttime temperatures are consistently dropping below fifty degrees, which in Austin is typically mid to late November and sometimes later. A season that runs from March through November is eleven months of active pressure, not the four or five months that most people assume.