Monsoon Season Pests in the Valley and What to Check After a Storm

Why monsoon season pests show up after summer storms

Arizona's monsoon season officially runs from June 15 through September 30, though most storms around Phoenix arrive in July and August. They bring heavy rain, strong wind and blowing dust, often in a short burst late in the day. Rain that falls fast on hard, dry ground runs off into washes and streets, and the soil around houses stays damp for a day or two afterward.

Monsoon season pests react to that change quickly. Rain floods the burrows, drains and nests where many of them spend the summer, and the warm, humid nights that follow make insects more active. Much of that movement heads toward houses, where slabs, walls and landscaping offer higher and drier ground.

Why roaches come up from drains and sewers after storms

American cockroaches live in sewer lines and storm drains through the summer. When heavy rain floods those lines, the roaches move up and out through manholes, cleanouts and yard drains, and some find their way into houses. Neighborhoods with older sewer lines often see the most of this.

A common entry point indoors is a drain nobody uses. Water sitting in the trap under a sink, tub or floor drain blocks roaches from coming up the pipe, but traps in a guest bathroom or laundry room can dry out in Arizona heat. Running water in those drains once a week keeps the traps full, and covers help on floor drains. Turkestan cockroaches, which live in water meter boxes and irrigation valve boxes, also move around more after a storm, and our cockroach control service treats both species.

How rain moves scorpions toward houses

Monsoon rain floods the ground-level spots where scorpions hide, such as cracks in the soil and the undersides of rocks, and it brings out the crickets and other insects scorpions eat. Scorpions respond by climbing block walls and moving onto patios and into garages, and many homes see a jump in scorpion sightings in late summer.

A blacklight check after a storm shows where they are moving. Our article on scorpion control in Arizona homes explains why they take steady work, and the scorpion control page describes how we treat them.

How monsoon rain leads to more mosquitoes

Aedes aegypti eggs can sit dry on the inside of a bucket or plant saucer for months, then hatch when rain fills it. Summer heat speeds the larvae along, and they can reach the biting stage in about a week, which is why mosquito numbers climb a week or so after the first big storm. Culex mosquitoes, which carry West Nile virus in Arizona, breed in larger standing water such as flooded low spots and green pools.

Emptying anything that caught rain within a few days of a storm keeps those eggs from becoming adults. Our post on why mosquitoes bite some people more covers personal protection, and our mosquito control service treats resting spots and water that cannot be drained.

Why ants move indoors during monsoon season

Rain that floods an ant nest forces the colony to move, and the workers carry their eggs and young to drier ground. Sometimes that ground is a wall void, the gap under a baseboard or the soil in a potted plant on the patio. Trails in kitchens and bathrooms are common in the days after a storm.

Monsoon rains also set off mating flights. Harvester ants and many other species send out winged males and queens after summer storms, sometimes in large numbers, and a flight usually lasts only a few hours. Winged ants look a lot like termite swarmers, so the difference is worth knowing.

Termite swarms after summer rains

Desert subterranean termites usually swarm in the evening after monsoon rains, and the swarmers fly toward lights. They are weak fliers and drop their wings soon after landing, so piles of wings on windowsills or near doors are a common sign. Swarmers do not damage wood themselves, but finding them inside the house usually means a colony is active in or under the house. Swarms outdoors mean colonies are active nearby.

If swarmers or shed wings turn up inside, collect a few in a zip-top bag and call for a termite inspection.

What to check around the house after a monsoon storm

A walk around the property the morning after a storm catches most problems early:

• Empty plant saucers, buckets, toys and tarps that caught rain.
• Turn off the irrigation timer for a few days after a heavy rain.
• Clear palm fronds, branches and debris that blew against the house or block walls.
• Look for mud tubes along the foundation and shed wings near windows and doors.
• Run water in unused sinks, tubs and floor drains so the traps stay full.
• Check door sweeps and the garage door seal for gaps.
• Switch outdoor lights to yellow bulbs, or turn off the ones nobody needs, to draw fewer insects.
• If ants are trailing inside, note where they come in and leave the trail for the technician to see.

Why pest service matters from July through September

July through September is when roaches, scorpions, crickets and mosquitoes are most active around Valley homes. Heavy rain and summer heat also shorten how long an exterior treatment lasts, so a gap in service during these months lets activity build quickly.

Homes on a monthly or bi-monthly plan get regular visits through storm season. On a quarterly plan, homeowners can call us if activity picks up between visits, since our re-service guarantee means we come back and re-treat covered pests at no extra charge. The pest control plans page explains each option, and new customers can start with a free inspection.