Every summer the same thing happens across the Las Vegas Valley. The first serious monsoon
storm rolls through, the washes run, and within a few days homeowners start finding scorpions
indoors, cockroaches in the garage, and rodents in the attic. It is not a coincidence.
The monsoon window
Southern Nevada’s monsoon season runs roughly July through September. KTNV Las Vegas has
reported pest control experts describing a spike in service calls to valley homes during that
window, driven by the sudden combination of heavy rain, standing water, and flooded drainage
channels in an environment that is otherwise extremely dry.
That window also overlaps with the annual peak in scorpion envenomations, which the
Journal of Medical Toxicology review found occurs nationally in August and September. Late summer is when the
two curves meet.
Why rain drives pests inside
Flooded harborage. Scorpions, spiders, and roaches shelter in block wall
voids, landscape rock, irrigation boxes, and wash banks. When those flood, the occupants move to
the nearest dry space, which is usually the inside of a building.
Standing water. Mosquito season in Southern Nevada runs April through October
under Southern Nevada Health District mosquito surveillance, and post-storm standing water in pool covers, planters, tyres, and
clogged drains produces new breeding sites within days.
Humidity. Cockroaches in particular respond quickly to a jump in humidity,
and monsoon moisture combined with irrigation gives them what a dry June does not.
Wash channels. Communities near the valley’s drainage system see this most
acutely. The Las Vegas Wash flows southeast through
North Las Vegas on its way to
Lake Mead, and the channel network is a documented flash flood corridor.
A pre-monsoon checklist
The right time to do this is June, before the first storm.
- Grade and drainage. Make sure water runs away from the foundation, and clear
drains and scuppers so water does not pool against the house. - Weep holes and door sweeps. Screen weep holes and fit sweeps on garage and
exterior doors. This is the main entry route for scorpions. - Seal penetrations. Utility, cable, HVAC, and plumbing entries.
- Clear harborage. Move firewood, pull landscape rock and dense ground cover
back from the foundation, and clear debris from the yard perimeter. - Eliminate standing water. Empty saucers, buckets, tyres, and pool covers
within 48 hours of a storm. Mosquitoes can complete a cycle very quickly in summer heat. - Trim vegetation off the structure. Branches touching the roof are a rodent
bridge and a scorpion route. - Get on service before July. A barrier established in spring performs far
better than an emergency call in August.
What to expect after a storm
Activity usually rises for one to two weeks after a significant storm, then settles. If you
are seeing repeated indoor sightings rather than a single incident, the issue is almost always an
entry point rather than a treatment gap, and it needs an inspection rather than another spray.
You can see how this plays out by area on our
Las Vegas,
Henderson, and
Spring Valley pages.
Need help now? Ridtechs Pest Solutions is a locally owned, Nevada-licensed pest control company serving the entire Las Vegas Valley. Call (702) 540-0931 or request an inspection.