Bugs in Northwest Houston, Season by Season: What Shows Up When

Spring is termite swarm season. Texas A&M AgriLife says swarms are most common from February through May in Texas, starting earliest in the south of the state. Native subterranean swarmers are about 1/4 to 3/8 inch long, colored anywhere from black to pale yellow-brown, and leave their wings on window sills and in cobwebs. Formosan termites, first found in Texas in 1956 near the Houston Ship Channel in Pasadena, swarm at night in late May and early June and fly toward lights.

Ants swarm at the same time of year, so check the waist: a termite has a straight body and four wings of equal length, while an ant is pinched in the middle and its front wings are longer. Fire ants wake up too. Texas A&M says their foraging does not start in earnest until the soil reaches about 70 degrees, and new mounds of fluffy, worked soil with no opening on top appear a few days after a heavy rain.

Summer belongs to mosquitoes, and they come in waves after rain. Texas A&M AgriLife entomologist Sonja Swiger describes floodwater mosquitoes first, aggressive biters from dawn to dusk; then container mosquitoes, black and white with striped legs, that breed in buckets, tires and gutters and bite mainly in the daytime, especially in shade; then Culex mosquitoes from stagnant water as it dries out. AgriLife's Mike Merchant names West Nile virus, carried by night-flying mosquitoes, as the biggest human threat from mosquitoes.

Wasps build through the summer. Paper wasp nests, most often under the eaves, are started in spring by queens that spent the winter in sheltered spots, and yellowjacket colonies grow to their largest by August or September, usually in the ground, sometimes in a wall void. Rain brings in the big roaches: AgriLife notes that large outdoor cockroaches head indoors during and shortly after rain, and American cockroaches, reddish-brown and 1 1/2 to 2 inches long, travel the sewer lines and come up through drains.

Fall is when rodents look for a way in. Texas A&M's school pest program notes that mouse problems can come at any time of year but especially in fall, when outdoor temperatures start to cool. Roof rats are climbers that live in attics and roof spaces and usually get in from overhanging trees or power lines, and an opening as small as 1/4 inch draws mice, 1/2 inch rats. Spiders and scorpions also move indoors as the weather cools.

Yellowjackets are at their worst now: Texas A&M says colonies are most often a problem in late summer and fall, and they raise next year's queens in October and November. Mosquitoes keep going too; the Texas Department of State Health Services says they stay active in much of Texas into November and December. Fall is also when Texas A&M's fire ant program suggests broadcasting bait over the whole yard, between late August and mid-October, so it works through the winter.

Winter is quieter outside, but the pests already indoors stay busy. Texas A&M calls roof rats quite common in east Texas cities, and footsteps in the ceiling or attic, droppings and gnaw marks are the usual signs; rats can also chew wiring. Our own count of Houston-area service visits found rodent work in every month from January 2025 through September 2026, so cold weather is not the only time to deal with it.

German cockroaches pay no attention to the weather. Texas A&M describes them as an indoor pest that hides near moisture and food in kitchens and bathrooms: light brown, about 1/2 to 5/8 inch long, with two dark stripes on the shield behind the head, and quick to multiply. Late winter also brings the first termite swarms; in South Texas, Texas A&M says they can start in January and February.