When Is Rodent Season in Phoenix? A Month-by-Month Calendar

What rodents are doing in the Valley each month, and the one job worth doing that month.

January: peak roof rat season

Cool nights and ripe citrus keep roof rats in attics, and January is one of our busiest months for attic calls. Roof rats are active mostly at night, so the usual sign is running or scratching overhead between dusk and dawn, plus droppings about half an inch long with pointed ends. House mice that moved in during the fall keep breeding indoors.
Do this: trap the rats already inside with snap traps on their runways, and keep poison out of the attic and walls.

February: citrus still feeding roof rats

Different citrus varieties ripen at different times, so a yard with mixed citrus can feed roof rats from roughly November through May. Fallen fruit matters even more than fruit on the tree, because it gives rats food and water in one place.
Do this: pick ripe citrus promptly, pick up fallen fruit, and do not compost citrus in an open pile near the house.

March: the last of the cool nights

Cooler nights through March still push rodents indoors. Roof rats that moved in over the winter are nesting in the attic insulation, soiling it with droppings and urine and flattening it along their runways.
Do this: once trapping has the attic quiet, seal the roofline: tile edges, soffit returns, roof vents and the AC line-set penetration.

April: roof rats still active

Spring is not the end of the season: Maricopa County lists roof rats as most active through May. Late citrus is still on the trees, and unskirted fan palms give roof rats dense, shaded nest sites within jumping distance of the roof.
Do this: skirt fan palms by removing the dead frond thatch, and cut branches back at least four feet from the roof (six feet is better).

May: the citrus season ends

The citrus that fed roof rats through the winter runs out around May, and they switch food: Maricopa County notes that roof rats eat queen palm fruit in summer when citrus is not available. As the heat builds, water becomes the limiting factor, and drip emitters and pool equipment pads are the steadiest water on many Phoenix lots.
Do this: get attic cleanup and new insulation done before summer, once the rats are out and the roofline is sealed.

June: heat, empty homes and rodents looking for water

In the summer heat, rodents look for water and cool shelter. The monsoon officially starts June 15. Homes closed up for the summer, common in Sun City, can host an infestation that starts in June and is not found until the owners return.
Do this: before leaving for the summer, have the attic, garage and roofline checked and any gaps sealed.

July: monsoon storms move rodents

July and August are typically the wettest months of the monsoon. Storm runoff floods ground burrows and wash-bottom middens, so Norway rats and pack rats that were living outside move to the edge of the house and then inside. Wind lifts roof tile, tears vent screens and loosens fascia, and each of those can open a gap of half an inch or more, which is all a rat needs.
Do this: walk the property in the week after a big storm: roof tile and eaves, vent screens, fascia, garage door seals and the weep screed line.

August: pack rats and car wiring

Pack rats whose middens wash out rebuild somewhere higher and drier: under a stored trailer, in a planter, behind pool equipment or in an engine bay. Chewed car wiring in August and September is almost always a pack rat, and homes near a wash or at the desert edge see the sharpest spike.
Do this: clear debris piles and blown palm fronds stacked against walls, and check under the hood of any car that sits unused.

September: storm damage shows up

The monsoon ends September 30. In the irrigated older neighborhoods, roof rat activity tends to show up two to six weeks after the storms, and the growth flush after the rains means branches that were a foot clear of the roof in June can be touching it by September.
Do this: trim the new growth back from the roofline and seal any storm gaps before the cool nights arrive.

October: rodent season begins

The first cool nights arrive, and roof rats start moving from the landscaping toward the house. House mice move indoors as nights cool, too. This is when our calls about rats in attics start to build.
Do this: book a free inspection. Anything already inside is trapped out before the gaps are sealed.

November: citrus ripens and attics fill

Citrus begins to ripen, and roof rats hollow out oranges and grapefruit from the side, leaving the empty rind hanging on the branch. November is also when Maricopa County's most active months for roof rats begin. Homes that sat closed all summer are often where the first droppings turn up as owners return.
Do this: check the attic. Listen after dark, and look for droppings, dark grease rub marks on rafters and pipes, and shredded insulation.

December: peak season

Cool nights, citrus on the trees and warm attics make December one of the busiest months for roof rats in Phoenix homes. Roof rats have three to five litters a year with up to eight young per litter, so waiting for an attic to go quiet on its own rarely works.
Do this: trap first, seal second, then clean the attic. Sealing before the rats are out shuts them inside.