Los Angeles Pest Calendar: What to Expect Month by Month

What does the Los Angeles pest year look like?

The year has three moods: a long dry season with irrigation-fed ants and drywood swarmers, a windy fall with Santa Ana conditions from October, and a short wet winter from November to April when storms push ants indoors. Each shift changes which pest a technician sees first.

Los Angeles does not have four tidy seasons for pests. The climate station near downtown, on the south side of Dodger Stadium, records under 0.05 inch of rain in each of July and August on average. That is the dry end of a long dry season, and it means that for months a pest's easiest water is whatever you give it, through sprinklers, drip lines, pet bowls, leaking hose bibs and the damp cabinet under a kitchen sink.

Wind and rain arrive as a second and third pressure. The Santa Ana season runs from October to March, and significant storm flow in washes such as Tujunga Wash comes only between November and April. Those are the two windows when pests are pushed from their normal places. The table below gives a month-by-month summary, drawing on UC IPM pest guidance, National Weather Service summaries and local climate normals.

Treat it as a guide rather than a timetable. A warm week in March or a surprise storm in October can move things earlier or later, and neighbourhoods near the canyon edge, the flats and the coast behave differently. If you want a longer look at any one pest, the other guides on this site go deeper.

What happens in the long dry season, May to September?

Irrigation becomes the main water source, and Argentine ant numbers rise within weeks of sprinklers running. In hot dry weather ants also search buildings for water. Gophers can dig in irrigated lawns and beds any time, and drywood termite swarmers begin flying in late summer.

From May the dry season begins, and UC research on Argentine ants in southern California shows that supercolonies spread with irrigation and fall back when irrigation stops. A back yard with drip lines under shrubs next to the house is therefore the most ant-friendly place in your garden. If a trail suddenly shows up on a kitchen counter in July, ants looking for water are a likely cause.

June is a good example of a month when gopher activity has nothing to do with the weather. In irrigated lawns, beds and gardens, digging conditions are good all year, so mounds can appear any time. UC IPM describes the typical crescent or horseshoe-shaped mound; if you see one in the middle of a watered slope, it is worth checking the rest of the bed.

By August the dry-heat pressure is at its peak, and drywood termite swarmers are about to fly. Swarmers are winged reproductives that leave a colony to start new ones, and in coastal and southern regions that tends to be late summer or early fall. A small pile of discarded wings on a windowsill is often the first sign. Our guide to Argentine ants and irrigation covers the ant side of this season in more detail.

• Check for sprinkler overspray hitting the wall of the house
• Look at shrubs and vines that touch siding, eaves or windows
• Inspect windowsills and light fixtures for shed wings after warm days
• Walk irrigated slopes and beds for fresh mounds

Why do Santa Ana winds matter for pests, from October to March?

Santa Ana winds bring dry northeast air, with humidity that can fall to single digits, and the season runs October to March. Fall is the worst fire-weather stretch after months of little rain. For pests, the main effects are fire-driven wildlife movement, drying vegetation and the lead-up to the first autumn rains.

The wind itself does not create a pest. What it does is set the scene: dry brush, parched hillsides and a landscape waiting for the first rain. The canyon edge in the Hollywood Hills holds coyotes, bobcats, deer, skunks, opossums, squirrels and raccoons, and animals can move through yards and alleys as they look for food and water in dry weather.

Wildlife is a different matter from household pests. This site does not trap, remove or relocate wildlife; those animals are governed by the California Department of Fish and Wildlife, and relocating nuisance raccoons and skunks is illegal. What a technician can do is work on the structure, sealing entry points, and you can reduce what draws animals by removing food and water, using tight-fitting lids and locking pet doors at night. Our guide to coyotes and raccoons at the canyon edge explains who to call.

October is also the month when several insect timelines overlap. Drywood swarmers can still fly, Argentine ant colonies merge into larger ones in the fall, and western subterranean termites swarm on calm sunny days right after the first autumn rains. That overlap is why October calls tend to be mixed.

What changes in the wet window, November to April?

From November the storm window opens, and ants may move indoors to get out of the rain. Argentine ant supercolonies stay large through winter, and baiting works best from winter to early spring. Gopher mounds appear on moist ground, and spring brings possible subterranean termite swarms on warm days after rain.

The wet season is shorter than most people expect, but it is intense. Significant flow in washes such as Tujunga Wash comes only between November and April, and that is also the window in which ants may move indoors out of the rain. If you see a trail appear in a bathroom or kitchen right after a storm, the cause is usually weather, not food.

December and January are the quiet months for most insects but the best months for one thing. UC IPM notes that bait stations are the most effective way to control Argentine ants, especially from winter to early spring, because the supercolonies are large and ants actively carry bait back to the nest. That is a reason to book an ant visit in winter rather than wait for the dry-season surge.

By March and April the rains end, Santa Ana season finishes in March and the landscape greens. Gopher mounds show up on moist ground, and subterranean termites can swarm, especially in southern California, on warm days after rain. A swarm in spring does not tell you how serious the infestation is, only that a colony is mature enough to produce reproductives.

When do termites swarm in Los Angeles?

Drywood termite swarmers typically fly in the daytime in summer and fall, tending to late summer or early fall in coastal and southern regions. Western subterranean termites typically swarm on calm sunny days right after the first autumn rains, and may also swarm in spring. Swarm timing varies by year and by weather.

Termite swarms confuse people because the two main types fly at different times and look different. Swarmers are winged reproductives, and finding them indoors is a sign that a colony is nearby, though not necessarily inside the house. Drywood swarmers leave from infested dry wood, and subterranean swarmers leave from soil.

Use the calendar as a reminder, not a diagnosis. If you find wings on a windowsill in September, a drywood species is likely. If you find a cloud of winged insects right after the first October rain on a calm, sunny day, a subterranean species is more likely. In both cases the next step is an inspection, which can tell you which type you have and where it is. Our guide to drywood versus subterranean termites explains the differences, and the termite inspection page covers what a visit looks like.

What should I do each season?

Match the task to the season: trim and check irrigation in the dry months, look for drywood clues and seal gaps before fall, schedule ant bait in winter, and walk your slopes in spring. A roof rat or wildlife concern is a year-round question that depends on trees, palms and entry points rather than the month.

A calendar is only useful if it changes what you do, so here is a short routine. In late spring, before the dry heat arrives, check that sprinkler heads do not soak the foundation and trim plants that touch the building. In late summer, look for pellets or wings. In fall, before the first rain, walk the roofline and seal obvious gaps.

Rats do not follow a calendar we can cite. We found no sourced month for roof-rat peaks, so we make no claim about one. What UC IPM does say is that roof rats climb, nest above ground in shrubs, trees and ivy, and in attics, wall voids and cabinets; keep 3 feet between branches and the roofline, trim palm frond skirts and thin oleanders. Our guide on roof rats, palms, citrus and attics goes into more detail.

• Spring: check slopes and beds for gopher mounds, and keep branches off the roof
• Summer: watch irrigation, trim plants touching walls and look for ants coming in for water
• Fall: seal gaps before the first rains and look for swarmer wings
• Winter: schedule Argentine ant bait while the supercolonies are large