There is no real off-season for mosquitoes in San Antonio. More than 220 frost-free days a year, clay soils that pond after every rain, and two distinct rainy windows in spring and fall keep Bexar County running as a near-ideal breeding environment for most of the calendar. The good news: the activity follows a predictable monthly curve. Time your yard treatments to that curve and you can stay ahead of peak pressure instead of chasing it.
Quick answer
Mosquito season in San Antonio typically runs from March through November, with peak activity in May, June, and September when temperatures stay above 50 degrees Fahrenheit and rainfall creates standing water. The Asian tiger mosquito is active even in mild winter months.
Dealing with this right now?
Ready to take back your yard? Contact Jenkins Pest to set up a mosquito barrier program timed to San Antonio's season and your outdoor schedule.
Want the full breakdown? See our residential pest control in San Antonio.
Key Mosquito Species in San Antonio
Two species dominate the San Antonio mosquito landscape. The southern house mosquito (Culex quinquefasciatus) bites at night and carries West Nile virus. It is the species behind most Texas transmission cases. It breeds in stagnant, organically enriched water: birdbaths, storm drain sumps, neglected pool covers, clogged gutters.
The Asian tiger mosquito (Aedes albopictus) is a daytime and dawn-dusk biter that has expanded throughout Bexar County. It breeds in very small water volumes. A bottle cap or a leaf axil holds enough. Texas A&M AgriLife Extension notes that the Asian tiger mosquito is more cold-tolerant than other species, which is why it can remain active during mild winter days in San Antonio.
There's a third to know about. The yellow fever mosquito (Aedes aegypti) is also present in South Texas and is associated with dengue, chikungunya, and Zika virus transmission. It likes urban environments and bites during daylight hours, near ground level.
Month-by-Month Mosquito Activity Calendar
January and February: Mosquito populations are at their seasonal low. The southern house mosquito overwinters as adult females in sheltered spots such as storm drains, culverts, and dense vegetation. Activity is limited to unusually warm days above 50 degrees Fahrenheit. Asian tiger mosquito eggs overwintered in moist soil can begin hatching during warm spells.
March and April: Things wake up. Rising temperatures trigger the first significant activity as overwintered southern house mosquito females begin seeking blood meals and laying eggs, while spring rains fill low spots and neglected containers. This is the window to act. Removing standing water now, before populations build, pays off all season.
May and June: Peak early-season pressure. Schedules shift outdoors and warm evenings make the biting impossible to ignore. Culex populations grow rapidly with longer days and warm nights, and the first mosquito-borne disease activity of the year typically shows up in Texas surveillance data during this window.
July and August: The heat changes the rhythm. Temperatures above 100 degrees Fahrenheit can temporarily depress adult activity during the hottest midday hours, but early mornings and evenings stay busy. Extended drought can actually shrink breeding habitat. The catch: the survivors that remain often bite more aggressively.
September and October: The second surge hits. Post-monsoon rainfall and cooling temperatures create a population spike that many San Antonio homeowners find worse than early summer. Fall evenings are prime outdoor time, and pressure runs high. This is often the busiest stretch for service calls.
November and December: Activity tapers sharply after the first sustained cold nights. However, southern house mosquitoes in storm drains and sheltered areas can remain partially active through December during mild winters like those common in South Texas.
Why San Antonio Has an Unusually Long Season
A few things stack up to stretch the season out. Winters here rarely hold a killing frost for more than a few days. Clay and caliche soils pond water after a rain instead of soaking it in. Mature tree canopy throws shade and traps humidity. And suburban yards are full of man-made objects that hold water.
Then there's groundwater. The Edwards Aquifer region produces consistent spring seeps and drainage features that hold water year-round in otherwise dry creek beds, and those features keep Culex populations going even during summer droughts when container breeding slows.
Standing Water: The Most Important Control Variable
The CDC identifies elimination of standing water as the single most effective mosquito control action homeowners can take. The overlooked sources are the ones that get you. Low spots in a caliche driveway hold water for days after a rain. Bromeliads and agave rosettes catch it right in their leaf axils. Rain barrels sit unscreened. So do the saucers under potted plants on a covered patio.
Speed is the reason this matters. The southern house mosquito can go from egg to biting adult in as few as seven days in summer temperatures. Leave standing water for a week, and you've grown the next wave yourself.
- Empty and scrub birdbaths weekly
- Drain saucers under potted plants after each rain
- Keep pool covers taut so they do not collect water
- Clean gutters before and after the spring and fall rainy seasons
- Check for low spots in the yard that pond after rain
- Store tarps and outdoor toys so they cannot collect water
Timing Professional Mosquito Treatments
Barrier spray treatments target adult mosquitoes resting in vegetation during daylight hours and hold up for roughly three to four weeks, depending on rainfall and temperature. Timing is the whole game. Start a barrier program in April, ahead of peak pressure, rather than waiting until June when populations are already high, and the season goes much smoother.
Larvicide can help too. Applying it to identified breeding sources such as storm drains, rain gardens, and low wet areas interrupts the population cycle earlier and complements the adult barrier treatments. A professional assessment pinpoints the specific water features and vegetation patterns on your property that drive the activity in the first place.