San Diego’s mild climate means no true pest-free season. Ants surge indoors in August through October during drought and again in November after the first rains. Drywood termites swarm September through November. Mosquitoes peak July through October. Fleas are worst April through October. Cockroaches are most active June through September. Rodents move indoors October through February. Spiders hit their mating peak in September and October. Knowing which pest is coming next is the most practical prevention tool a homeowner has.
San Diego doesn’t get a January freeze that resets the pest clock. What we get instead is a rotating cast of problems tied to temperature swings, drought, and the first rains of fall. Pests that slow down in genuinely cold climates stay active here longer, and some never stop entirely. This calendar gives you the honest picture of what’s coming each month so you can stay ahead of it.
The San Diego pest season at a glance
Use this table as your quick reference. It shows the primary activity window and the realistic pressure level for each pest in our climate.
| Pest | Peak months | Low months | What triggers activity |
|---|---|---|---|
| Argentine ants | Aug–Oct (drought surge), Nov–Jan (rain surge) | May–Jul | Late-summer heat dries soil; first rain in fall drives them into walls |
| Drywood termites | Sep–Nov (swarm season) | Dec–Feb | Warm dry afternoons in late summer and fall |
| Subterranean termites | Feb–May (swarm season) | Jul–Sep | Warm afternoons after heavy winter or spring rain |
| Aedes mosquitoes | Jul–Oct | Nov–Mar | Standing water, warm temps above 60°F, humidity |
| Fleas | Apr–Oct | Dec–Feb | Warm humid months; pets carrying them from yard to indoors |
| German cockroaches | Jun–Sep | Jan–Mar | Heat, humidity, food sources; peak in kitchens and restaurants |
| American cockroaches | Year-round, peak May–Sep | Dec–Feb | Warm sewers and crawlspaces; flee into structure in heat |
| Roof rats | Oct–Feb (indoor pressure) | May–Aug | Fruit ripens; cooler nights drive them to seek warmth inside |
| House mice | Oct–Mar | Jun–Aug | Cooling temperatures pull them toward interior wall voids |
| Black widow spiders | Sep–Oct (mating peak) | Dec–Feb | Males wander in fall; females build webs in cluttered dry spaces |
| Gophers | Feb–May, Sep–Nov | Jul–Aug | Active during mild temps; slow in extreme heat |
| Bed bugs | Year-round | None | Travel and secondhand furniture; no seasonal tie |
Month-by-month breakdown
January and February
Pest pressure is as low as it gets in San Diego, but it doesn’t disappear. Subterranean termites start swarming on warm afternoons after rain as early as February, so if you see dark-winged insects clustering near soil or a foundation crack after a wet week, that’s your cue to call for an inspection. Argentine ants carry over from the fall rain surge and can still be active indoors. Rodent pressure stays elevated from the fall move-in; if you haven’t sealed entry points, rats and mice found comfortable wall voids in October and are still in them now.
What to do: check under sinks and around water heaters for rodent signs, confirm door sweeps are intact, and keep firewood stacked away from the house.
March and April
Spring is subterranean termite swarm season. Western subterranean termites swarm on warm afternoons after a good soaking rain, and the SD County window runs roughly February through May. See our detailed San Diego termite swarm calendar for how to tell swarmers from flying ants and which treatment approach fits which species.
Ants start foraging more actively as soil warms. Fleas begin their climb as temperatures rise and wildlife activity increases. This is the month to treat your yard and pets before the flea population builds.
What to do: schedule a termite inspection if you haven’t had one in two years, start flea prevention on pets, and clear yard debris that shelters ant colonies.
May and June
This is the transition month. Subterranean termite swarms are winding down. Cockroaches ramp up fast as temperatures climb. German cockroaches, the small tan ones common in kitchens and apartments, become significantly harder to control once heat arrives. American cockroaches come up from drains and sewers as the outdoor temperature pushes them to seek stable environments.
Mosquitoes begin establishing as daytime highs stay reliably above 70°F. The invasive Aedes aegypti and Aedes albopictus mosquitoes that have spread through the county can breed in as little as a tablespoon of standing water, so any container holding water outdoors becomes a source. Read more on mosquito control in San Diego and what the county’s own Aedes monitoring data shows about where the population is densest.
What to do: audit outdoor containers, birdbaths, and gutters for standing water, deep-clean kitchen areas before cockroach season peaks, and inspect window screens.
July and August
This is cockroach season. German cockroaches reproduce fastest in the heat, and infestations that were manageable in spring can grow significantly through July and August. American cockroaches are active in outdoor areas and crawlspaces. Cockroach control in San Diego is harder in summer because the population rebound between treatments is faster.
Mosquito season peaks. The Aedes mosquitoes active in San Diego bite during daytime, not just dusk, so the usual advice to avoid going out at dawn and dusk doesn’t fully apply here. See the San Diego County Aedes mosquito data for 2026 for trap counts by city.
Argentine ants begin their late-summer drought behavior. As creek beds and soil dry out, colonies follow moisture into homes through micro-cracks in foundations and gaps around pipes. You’ll often see trails moving toward kitchens and bathrooms first.
What to do: eliminate standing water every week, treat cockroach pressure before it compounds, watch for ant trails along exterior walls and into kitchens.
September and October
September and October are the most active pest months in San Diego County.
Drywood termites swarm during warm dry afternoons, typically September through November. These are the most common termite in San Diego, and their swarmers are light-colored with equal-length wings. If you see piles of discarded wings on windowsills or around light fixtures in the evening, a colony is already established in the structure. Unlike subterranean termites, drywood termites don’t need soil contact, which means they can infest attic framing, furniture, and wall voids anywhere in the home.
Argentine ant pressure hits its second peak of the year when the first fall rains arrive. Heavy rain saturates ant colonies in soil, forcing thousands of workers inside through any available gap. This is the surge that most homeowners remember as “sudden” because it happens fast, overnight after a storm.
Black widow spiders hit their mating peak in September and October. Male widows wander searching for females, which is when they end up in shoes, garages, and storage boxes they’d normally avoid. Female black widows build webs in dark undisturbed spaces year-round, but encounters spike in fall.
Rodents begin their annual indoor migration as nights cool. Roof rats follow fruit ripening on citrus, avocado, and fig trees before moving toward the structure once the fruit drops or freezes.
What to do: schedule a drywood termite inspection, seal ant entry points before rain season, seal garage door gaps and exterior openings before rats move in, check shoes and gloves before putting them on.
November and December
Drywood termite swarms taper off by late November. Subterranean termites can swarm on warm days in November and December in coastal areas, but it’s lighter activity than spring.
Argentine ant pressure stays elevated as rain continues. The colony movement triggered by rain in October often continues through December as ants re-establish indoor foraging trails.
Rodent pressure peaks. October through February is when roof rats and house mice are most likely to be actively living inside walls and attics. If you hear scratching overhead at night or find droppings in the pantry, don’t wait.
Fleas drop off significantly but don’t disappear. A warm December can extend flea season in sheltered outdoor areas, and pet owners often see indoor flea populations persist through winter.
What to do: inspect the attic and garage for rodent entry, continue ant treatment through rain season, check pets for fleas monthly even in winter.
The two triggers that drive most San Diego pest problems
Almost every surge in the calendar above ties back to two climate events: prolonged drought and the first fall rains.
Drought behavior. When San Diego goes weeks without rain and temperatures stay high, ant colonies lose soil moisture and forage outward looking for water. This is why late-summer ant invasions often show up at kitchen sinks and bathroom drains first. The same moisture stress pushes other pests into structures.
First rain surge. When rain finally comes after a dry stretch, it saturates the soil rapidly. Argentine ant colonies, whose nests live just below the surface, flood and scatter. Workers relocate inside and establish new foraging trails almost overnight. This is the most predictable pest event on the San Diego calendar, and it happens every year between October and January.
Pest control that’s timed around these two events, treating exterior perimeters before drought stress peaks and again before rain season, outperforms reactive treatment every time.
Frequently asked questions
When is pest season in San Diego?
San Diego doesn’t have a single pest season. Ants peak in late summer and again after fall rains. Termites swarm in spring (subterranean) and fall (drywood). Mosquitoes and cockroaches are worst in summer. Rodents move indoors in fall and winter. Planning around each pest’s specific window is more useful than treating for a generic “pest season.”
When is cockroach season in California?
In San Diego, cockroach pressure peaks from June through September when heat and humidity accelerate reproduction. German cockroaches can complete a generation in about 100 days at room temperature and faster in summer heat. American cockroaches are active outdoors year-round but move into structures more in summer. Restaurants and multifamily buildings see the highest pressure in July and August.
When is mosquito season in San Diego?
Aedes mosquitoes in San Diego are active when daytime temperatures stay above 60°F and standing water is available. That window runs roughly May through October, with peak activity in July through September. Unlike the native Culex mosquitoes that bite at dusk, the invasive Aedes species established in San Diego County bite during daytime and breed in very small containers. See the county’s trap data for specific neighborhoods.
When is flea season in San Diego?
Flea season in San Diego runs April through October, with the heaviest pressure in July and August. Fleas are active whenever temperatures stay between 65 and 80°F with moderate humidity. San Diego’s mild climate means fleas rarely disappear entirely in winter, especially on pets that go outdoors. Year-round flea prevention on pets is more effective than seasonal treatment.
When is termite season in California?
In San Diego, termite season depends on species. Subterranean termites swarm February through May on warm afternoons after rain. Drywood termites, the most common species here, swarm September through November on warm dry afternoons. Because San Diego stays mild year-round, termite damage continues in all months even when swarming isn’t happening. Annual inspections catch active infestations before swarm season.
When is ant season in San Diego?
Argentine ants in San Diego have two peak periods: late summer (August through October) when drought pushes them indoors searching for water, and fall through early winter (October through January) when the first rains flood their soil nests and force them inside. A warm San Diego winter can mean ant pressure persists through February. Treatment before both windows is the most effective approach.
If you’re seeing pests outside their typical window or dealing with a problem that’s gotten ahead of prevention, call us at (858) 925-5546. We cover all of San Diego County and can usually get out the same day.