Winter invaders: how do you keep pests out when temps drop?

Southern California winters are mild, which is the problem. A December night in Murrieta or Menifee drops to near freezing, the day warms back up, and the pests that would die off in a real winter instead look for somewhere that stays warm overnight. That's your house.

This guide is about the structure. The rain has its own guide, and so do rodents and winter cleaning. This one covers which insects and spiders move in on cold nights, exactly where they get through, and a weekend's worth of sealing that closes most of it. The pest biology follows UC IPM.

The gaps below are worth checking on any house in Southwest Riverside or North San Diego County. Here's the list.

Which pests move in when temperatures drop in Riverside County?

Five groups. Spiders first. Western black widows, which UC IPM lists around garages, wood piles and block walls, don't die back in our winters, and on cold nights they shift to the garage, the shed and the stacked boxes along the wall. Brown widows stay outside, on patio furniture, fences and eaves. Earwigs second: they shelter in damp mulch and leaf litter by day, and on cold nights the mulch against a warm foundation wall is the warmest mulch around, so they end up at the base of the door. Argentine ants third: they don't disappear in a mild inland winter, and in cold weather the trails follow warmth, which means the hot water line, the dishwasher, the water heater closet and the slab under the kitchen. Cockroaches fourth: the American cockroach comes up from drains and the space under slabs toward warm, damp spots behind the refrigerator and under the sink. Paper wasps fifth: the mated queens leave the nest in fall and look for a dry, protected crack to spend the winter in, and attic vents, eave gaps and the space behind shutters are where they end up.

Where winter pests get into a house

Through gaps that were there in summer and didn't matter. Start low. The bottom corners of the garage door, where the rubber seal has worn, are a common entry for spiders, earwigs and ants. The gap under an exterior door with no sweep, which shows as daylight when you lie on the floor. Weep screeds at the base of the stucco and weep holes in the block wall. The hole around the hose bib, the gas line, the air conditioner lines and the cable entry, cut oversize and never sealed. Then go up. Dryer vents with a broken flap. Attic and crawl space vents with torn or missing screens. Gaps where the eave meets the wall and where two rooflines join, which is where wasp queens and roof rats both go. Window screens with a tear, and the track of the slider. A chimney without a cap. The rule is simple: if you can fit a pencil into it, an insect or a spider has already found it. Walk the whole perimeter once in daylight and once at night with a flashlight, because the night walk shows you which gaps are in use.

How to seal a house against winter pests in a weekend

Saturday is outside. Replace the garage door bottom seal and add corner plugs. Fit sweeps to the exterior doors that show daylight. Pack the gaps around the hose bib, gas line and air conditioner lines with copper mesh or steel wool and seal over it with exterior caulk, since mesh alone stops rodents and caulk alone stops insects, and you want both. Screen the weep holes in the block wall with fine mesh. Replace the broken dryer vent flap. Caulk the gap where the patio slab meets the stucco. Sunday is up high. Replace torn vent screens on the attic and crawl space with metal mesh no larger than 1/8 inch, which keeps out wasp queens as well as rodents. Seal the gap where rooflines meet with mesh and caulk, or get a professional to do it if it means a ladder on a two-story. Fit a chimney cap. Then the yard: pull mulch and leaf litter back from the foundation, move the wood pile off the wall and off the ground, cut the palms and vines back from the roofline. None of it needs a product, and all of it makes a treatment work better.

Why the garage is the winter pest hotel

Because it's warmer than outside, drier than the yard, darker than the house and full of boxes nobody moves. Black widows want exactly that, and UC IPM names garages as one of the places they're most common. Cardboard boxes on the floor against the wall, the gap behind the water heater, the underside of the workbench, the folded patio umbrella, the kids' bikes that don't get ridden in December: all of it is web territory. Earwigs come in under the door and settle in the damp corner where the washer drains. Argentine ants trail along the warm wall by the water heater. The structural fix is the door: the bottom seal, the corner plugs and the gap where the side door meets the frame, plus the holes where the water heater vent and the washer drain go through the wall. Leave a clear strip along the walls so our technician can reach them. The cleaning side, storage off the floor and boxes out of cardboard, is in our winter cleaning tips post.

Do wasps come back in winter?

The nest doesn't, but the queens do. Paper wasps, the long-legged ones that build the open comb under eaves in Temecula and Murrieta all summer, abandon the nest in fall. The workers die, and the mated queens look for a dry, protected spot to spend the winter: inside attic vents, behind shutters, in the gap where the eave meets the wall, under loose fascia, inside the hollow of a patio umbrella. You'll see them on warm December afternoons, slow and confused, at a south-facing window or crawling on the inside of an attic hatch. One queen in a room is a window to open. The reason it matters is spring. A queen that survives the winter in your eaves can start a new nest close by, so the nest over the front door in April may have started as a queen in the attic vent in November. So the winter job is the screen on the attic vent and the gap at the eave, done now. We remove wasp nests. We don't handle bees.

Why Argentine ants follow the plumbing in cold weather

Because that's where the warmth is. Argentine ants keep working through a mild Southern California winter wherever the ground stays warm. The slab under a kitchen, the soil around a hot water line, the wall void behind a dishwasher and the water heater closet all hold heat overnight, so the trails in January run along those lines instead of across the patio. That's why a winter ant trail so often comes out from behind the dishwasher kickplate or up through the gap where the sink drain enters the cabinet floor. The fix is the same as in summer, placed differently. Seal the gap at the drain and the dishwasher supply line where they come through the cabinet floor. Fix any drip under the sink, since a warm, wet cabinet is the best thing a cold ant colony could find. And don't spray the trail, since repellent sprays push the colony to a new route and leave the queens untouched. Slow-acting bait along the active trail, which the workers carry back, is what UC IPM recommends for Argentine ants.

What a winter pest control visit should cover

With any company, ask for the eaves first. Brushing the eaves in winter knocks down the webs, the egg sacs and the dead insects that would feed next season's spiders. It's part of every visit we make, and on the Quarterly plan that's a visit every three months. Beyond that, ask the technician to look at the gaps listed in this guide and point out the ones you can seal yourself and the ones that need a ladder or hardware cloth. Ask where the winter ant trails are running, since they'll be along warm plumbing instead of the patio. Ask what was applied and when the kids and pets can go back on it, because the re-entry time is set by each product's label, and our technician will tell you without being asked. And note the technician's name. Where we can, a technician stays in the same part of our area, though we can't promise you'll see the same person each time. The state licenses each of them.

A cold snap versus a cold winter

The difference is suddenness. A gradual cooling in November lets pests shift to shelter over weeks, and the garage fills slowly. A cold snap, when a Menifee or Hemet night drops near freezing after a warm week, moves everything at once, and that's the morning you find twenty earwigs at the base of the slider, ants in the bathroom and a black widow on the garage floor that was in the wood pile the day before. The cold snap also exposes which gaps are live, because the pests take the shortest route to warmth and leave a trail you can follow. So when the forecast shows a freeze warning for the Inland Empire, do the night walk with the flashlight the evening before and the morning after, and seal what you find in use. The sealing checklist in this guide is the same whether the winter is mild or hard. What a cold snap changes is the urgency, and speed is the thing our customers mention most when they say why they chose us. Call (951) 535-4220 and give Jenni your address. She'll book the next opening.