Rodents After the Monsoon: What Wet Summers Change
A wet summer can mean more mice by fall. NMSU Extension notes that hantavirus risk tends to rise in years when rodent populations increase, such as after wet years. More rain means more seed and cover in the brush around town, and more mice looking for shelter once the nights cool.
Monsoon storms also knock things loose around the house. After the rains, walk the outside, fix what the storms opened and get ahead of the fall move indoors.
Why rain matters to rodents
Desert rodents breed more when there's more to eat. Summer rain greens up grasses and shrubs, which produce seed, and the brush along arroyos and open space fills in. The payoff shows up weeks later, when a bigger crop of young mice spreads out looking for territory.
That's the link NMSU draws to hantavirus. More deer mice means more chances for people to run into droppings in garages, sheds and cabins. The New Mexico Department of Health's advice stays the same in any year: ventilate closed spaces, soak droppings with bleach solution and never sweep them.
Storm damage to check
After a big storm, look for openings the wind and water created:
- Vent screens bent, torn or blown loose
- Soil washed away along the foundation, exposing gaps at the base of the stucco
- Garage door seals pushed out of place by debris
- Swamp cooler panels and duct seals knocked loose
- Canales and parapet caps with new gaps
- Fences and block walls with new openings at the base
Yard debris and new cover
Storms pile up branches, leaves and trash against walls and fences, and that's instant cover. Clear it. Fast-growing weeds after the rain also give rodents room near the house. Inside city limits, owners have to cut weeds taller or wider than 4 inches, out to the curb and to the middle of the alley. See the property rules guide.
Pack rats rebuild after storms, too. Check the base of junipers and the area under decks for new stick piles. Pack rat nests shows what to look for.
Arroyos and drainage
Homes along arroyos and drainage channels see the most movement after rain. Water pushes rodents out of low burrows and nests, and the arroyo corridors carry them into neighborhoods. Lots near the Bear Canyon and Embudito arroyos in the foothills, the Tijeras Arroyo near Four Hills and the Amole Arroyo by Westgate are all worth a close look after a storm.
Getting ready for fall
Late summer is the best time to seal, since mice tend to move indoors in fall and winter. The state rodent guide says to seal any hole bigger than a quarter inch with gnaw-resistant material like hardware cloth, sheet metal or concrete. Keep firewood on racks 18 inches off the ground and maintain a weed-free strip about 3 feet wide along the foundation.
If the storms opened more than you can handle, a prevention and monitoring visit after the monsoon covers sealing touch-ups and a check for new activity.
Indoors after a wet summer
If you notice droppings in the garage or pantry in late summer or early fall, act early. Clean them with the soak-and-wipe method, set snap traps along walls and look for the gap. A small problem in September is easier than a large one in December. NMSU recommends snap traps placed along travel routes, at right angles to the wall, and checked daily.
If you keep catching mice, a professional inspection will find entry points you missed. See rodent inspection.
Cabins and outbuildings
Cabins in the East Mountains and sheds on rural lots feel the effect of a wet year most. If you closed up a cabin before the monsoon, assume mice found it. Air it out before going in, and follow the deer mice in garages and sheds steps.
Swamp coolers after the season
Many Albuquerque homes switch from evaporative coolers to heat in fall. When the cooler is shut down, its duct and the gaps around the roof curb can become a way in. Cover or seal the duct for winter and check the curb for gaps. Mice and pack rats that climb to the roof will find an open cooler, and from there the ductwork leads straight into the house.
Storm cleanup safety
Clearing storm debris can mean moving piles where rodents were sheltering. Wear gloves and long sleeves, and don't reach into piles bare-handed. If you uncover a nest or droppings, wet them with bleach solution before moving them. In foothill and East Mountain areas, the city collects dead rodents and rabbits that died without injury for plague testing, so call 311 instead of handling one.
Wash up thoroughly when you're done, and wash work gloves or throw them out if they touched droppings or nest material from the debris pile.
Also asked
Does a wet year really mean more mice?
NMSU notes hantavirus risk tends to rise after wet years when rodent populations increase. More food usually means more mice.
When should I seal after the monsoon?
As soon as the storms ease, before the first cold nights.
Do floods push rats into houses?
Water pushes rodents out of low ground. Homes near arroyos and ditches see more of it.