Published pest sources describe seasons, not calendar dates. UC IPM says subterranean termites swarm “during the afternoon in either spring or fall on clear days after a soaking rain,” drywood swarmers appear “during daytime hours during summer and fall,” and flea numbers “increase dramatically during spring and early summer.” The County of San Diego says invasive Aedes mosquitoes are “most active in San Diego during summer and fall.” This calendar is built on those windows, and on the prevention work that fits each one.
San Diego doesn’t get a hard freeze that resets the pest clock. What you get instead is a rotating set of problems tied to rain, warmth, and irrigation.
The San Diego pest season at a glance
Use this table as your quick reference. Each row shows the timing window the cited authority describes, in its own words.
| Pest | What the source says about timing | Source |
|---|---|---|
| Subterranean termites | Swarms “during the afternoon in either spring or fall on clear days after a soaking rain” | UC IPM |
| Drywood termites | Swarmers “occur during daytime hours during summer and fall” | UC IPM |
| Aedes mosquitoes | ”most active in San Diego during summer and fall” | County of San Diego |
| Fleas | Numbers “increase dramatically during spring and early summer” | UC IPM |
| Argentine ants | Treatments “made in late winter and early spring when ant populations are just beginning to grow will be most effective” | UC IPM |
| Cockroaches | German cockroaches favor “warm (70° to 75°F), humid areas that are close to food, water, and dark areas for harborage” | UC IPM |
| Rats and mice | Exclusion is year-round work: “All holes larger than 1/4 inch should be sealed to exclude both rats and mice” | UC IPM |
| Black widow spiders | No season named. Human structures provide ideal habitat, and “In such supportive habitats, mature females can be found every few feet” | UC IPM |
| Gophers | In irrigated ground, “digging conditions are usually optimal year-round, and mounds can appear at any time” | UC IPM |
| Bed bugs | No seasonal tie. People “bring bed bugs into their homes on luggage, clothes, bedding, furniture, or other objects” | UC IPM |
Month-by-month breakdown
January and February
Winter is the quiet end of the year, and it’s the best time to do the work that pays off later. UC IPM says ant “Treatments made in late winter and early spring when ant populations are just beginning to grow will be most effective,” which makes this the window to act rather than the window to wait.
Watch for subterranean termite swarmers after a wet stretch. UC IPM describes them swarming “during the afternoon in either spring or fall on clear days after a soaking rain,” and adds that “Seeing swarms of flying termites does not always mean your home or building is infested.”
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 the subterranean termite window UC IPM describes, and it says “Spring time, especially a warm, sunny day following rain, is the optimal time for subterranean termite swarming behavior.” See our detailed San Diego termite swarm calendar for how to tell swarmers from flying ants and which treatment approach fits which species.
Fleas start climbing now. UC IPM says you “can find fleas on pets throughout the year, but numbers tend to increase dramatically during spring and early summer when conditions favor larval development.”
What to do: schedule a termite inspection if you haven’t had one recently, start flea prevention on pets, and clear yard debris near the foundation.
May and June
Two things overlap here. Fleas are in the spring and early summer climb UC IPM describes, and mosquito season is starting. The County of San Diego says invasive Aedes mosquitoes lay eggs “in small containers of standing water, often in your backyard,” that a quarter inch of water is enough, and that you should “Dump out standing water sources both inside and outside at least once a week.”
Cockroach pressure tracks warmth and harborage rather than a date. UC IPM says the German cockroach, the most common indoor species in California, prefers food preparation areas, kitchens, and bathrooms, favoring “warm (70° to 75°F), humid areas that are close to food, water, and dark areas for harborage.” Read more on mosquito control in San Diego and what the county’s own Aedes monitoring shows.
What to do: audit outdoor containers, birdbaths, and gutters for standing water, deep-clean kitchen areas, and inspect window screens.
July and August
Summer is one half of the Aedes window. The county describes these mosquitoes as ones that “Bite during the day, especially around the legs and ankles” and that “Can bite aggressively and multiple times,” which is why the usual dawn-and-dusk advice doesn’t fit here. See the San Diego County Aedes mosquito data for 2026 for what the county reports by area.
Summer is also the start of the drywood termite swarm window. UC IPM says “The most common sighting of drywood termites is flying adults (called swarmers) that occur during daytime hours during summer and fall.”
For cockroaches, the lever is harborage and food. Cockroach control in San Diego covers what a licensed company targets. UC IPM notes that “Adult German cockroaches can hide in a crack 1/16 inch wide,” which is a useful sense of how small a hiding place counts.
What to do: eliminate standing water every week, close up cracks in kitchen cabinetry, and watch for ant trails along exterior walls.
September and October
Fall is where several windows overlap in the published sources.
Drywood termite swarmers are still in their “summer and fall” window. UC IPM notes these termites “are difficult to detect since they live deep inside wood and are rarely seen until they swarm,” and that determining the extent of an infestation “requires experience and is best done by a professional.”
Subterranean termites can swarm in fall too, not just spring. UC IPM describes swarms “in either spring or fall on clear days after a soaking rain,” and says that “On warm, sunny days following fall or spring rains, swarms of reproductives may be seen emerging en masse from their underground nests.”
Argentine ant activity indoors is about entry points rather than a date on the calendar. UC IPM’s advice is to “Look indoors and outdoors for holes or cracks in foundations or walls that provide entry points to buildings,” and it warns that “Spraying ants indoors with pesticides will not prevent more ants from entering.”
UC IPM’s widow guidance names no season at all. It says that because the holes, cracks, crevices, trash, and clutter associated with human structures provide ideal habitat, “these spiders are often very common around homes, barns, outbuildings, and rock walls.” Its storage advice is worth doing now: “When cleaning up clutter in garages and other storage areas, be sure to wear gloves to avoid accidental bites.”
What to do: schedule a drywood termite inspection, seal ant entry points before rain season, seal exterior openings, and wear gloves in storage areas.
November and December
Rain brings the second subterranean swarm opportunity UC IPM describes for fall, and it brings the sealing deadline for rodents. UC IPM’s rat guidance is specific: “All holes larger than 1/4 inch should be sealed to exclude both rats and mice,” and it says to make sure “all exterior doors are tight fitting and sealed at the threshold.” The CDC’s guidance is the same shape: “Look for gaps and holes in and around your home” and “Seal up any gaps and holes you find to prevent rodents from getting in.”
Roof rats are worth knowing by their food. UC IPM says they “prefer fruits, tree nuts, berries, slugs, snails, young birds, and bird eggs” and “consume avocados and citrus fruits, often while still on the trees.” If you have fruit trees, the advice is to “Remove fallen fruit and nuts that have dropped from trees.”
What to do: inspect the attic and garage for rodent entry, continue ant prevention through rain season, and check pets for fleas.
The one trigger that sets its own date
Across the termite guidance, one event shows up again and again: rain followed by a warm day. UC IPM ties subterranean swarming to “clear days after a soaking rain” and calls a “warm, sunny day following rain” the optimal condition for it. That’s the one date on this calendar that nature sets rather than the almanac.
It’s also a caution rather than an alarm. UC IPM notes that “Since most soil around a home has buried cellulose debris (roots, stumps, or fence posts), finding swarming termites in your yard doesn’t necessarily mean your house has termites.” A swarm is a reason to get an inspection, not a diagnosis on its own.
Timing your general pest control around the ant window UC IPM names, late winter and early spring, and around the rain-linked termite windows, is a more useful plan than treating on a fixed monthly schedule.
Frequently asked questions
When is pest season in San Diego?
There isn’t a single one. The published windows are different per pest: subterranean termites swarm in spring or fall after soaking rain, drywood termite swarmers show up during summer and fall, invasive Aedes mosquitoes are most active in summer and fall, and fleas increase in spring and early summer. Rodent exclusion and bed bugs have no season at all.
When is cockroach season in California?
UC IPM describes cockroach preferences rather than months. The German cockroach favors “warm (70° to 75°F), humid areas that are close to food, water, and dark areas for harborage,” which means the season is wherever those conditions exist. Ask a company what harborage it found rather than what month it is.
When is mosquito season in San Diego?
The County of San Diego says invasive Aedes mosquitoes are “most active in San Diego during summer and fall.” They “Bite during the day, especially around the legs and ankles,” and the county’s core instruction is to “Dump out standing water sources both inside and outside at least once a week.”
When is flea season in San Diego?
UC IPM says fleas can be found on pets throughout the year, but that “numbers tend to increase dramatically during spring and early summer when conditions favor larval development.” It also notes that “In California, outdoor flea populations are most prevalent in coastal localities and other places with moderate daytime temperatures and fairly high humidity levels.”
When is termite season in California?
It depends on species. UC IPM says subterranean termites swarm “during the afternoon in either spring or fall on clear days after a soaking rain,” while drywood swarmers “occur during daytime hours during summer and fall.” Because drywood termites live deep inside wood and are rarely seen until they swarm, an inspection is what settles it.
When is ant season in San Diego?
UC IPM doesn’t give San Diego a month range, but it does give a timing rule for treatment: “Treatments made in late winter and early spring when ant populations are just beginning to grow will be most effective.” It also notes that for Argentine ants, “sweet baits are attractive year-round” while “Protein baits are attractive to Argentine ants primarily in the spring.”
If you’re seeing pests outside their typical window or dealing with a problem that’s gotten ahead of prevention, call us at (858) 400-6561. We match homeowners across San Diego County with licensed local companies, and the matched company inspects and quotes before any work begins.