Pest Notes, Publication 7438 Revised December 2018 Integrated Pest Management for Home Gardeners and Landscape Professionals Ground Squirrel round squirrels (Figure 1) are troublesome Grodent pests for many home gardeners. The California ground squirrels, Otospermophilus beecheyi and Otospermophilus douglasii, are the most common species in and around homes and gardens. The two are usually not referred to as separate species, so in this publication they are referred to as “California ground squirrel” or Figure 1. California ground squirrel, Otospermophilus sp. simply “ground squirrel.” The California ground squirrel is found Although California ground squirrel throughout most of California and populations generally thrive where the extends south into the northwestern winters are mild, there are known pop- part of the Baja peninsula (Figure 2). ulations in the central Sierra Nevada It is also found in western Nevada and Mountains at altitudes of over 7,000 can be found north of the Columbia feet. River in south central Washington and throughout western Oregon. IDENTIFICATION The California ground squirrel can It is easy to identify ground squirrels invade and colonize residential areas since they forage above ground near that have open grassy areas, sometimes their burrows. Their body measures 14 causing considerable damage. to 20 inches, which includes their tail. Adult squirrels weigh between 21 and 30 ounces. The males are somewhat larger than the females. Ground squirrel fur is mottled brown, Authors: with some white and gray markings on Niamh M. Quinn, UC Cooperative the back (Figure 1). Their belly and un- Extension, San Diego, Orange, and derside have a combination of lighter Figure 2. Range of the California Los Angeles Counties and South Coast browns, grays, and white. California ground squirrel. Research & Extension Center. ground squirrels have a white ring Monica J. Dimson, UC Cooperative around each eye. Their tails are some- Extension, Orange County. what bushy (but less so than those of retreat to a burrow, whereas tree squir- tree squirrels) and their ears are erect rels will climb a tree or tall structure Roger A. Baldwin, Dept. of Wildlife, and conspicuous. and never use a burrow. For informa- Fish, and Conservation Biology, UC tion about tree squirrels, see the UC Davis. Although ground squirrels look similar to tree squirrels and can climb trees, IPM Pest Notes: Tree Squirrels. when frightened they generally will Pest Notes: Ground Squirrel Page 2 of 7 BIOLOGY AND BEHAVIOR California ground squirrels live in colonial burrow systems where they sleep, rest, rear young, store food, and avoid danger. Their burrows are about 4 inches in diameter, although older burrow entrances can occasionally be quite a bit larger (Figure 3). The length of burrow systems usually ranges between 5 and 30 feet. Most burrow systems are within two to three feet of the surface of the ground, but they may occasionally be up to 6 feet or more in depth. Burrows can be single tunnels or complex branching systems. They may be occupied by a single squirrel or occupied by many. Figure 3. California ground squirrel Figure 4. Ground squirrel damage to burrow opening under structure. avocado. California ground squirrels are active during the day, mainly from midmorn- ing through late afternoon, especially Ground squirrels are primarily herbiv- Burrows and mounds make it difficult on warm, sunny days. They have two orous, and their diet changes with the to mow lawns and other grassy areas, periods of dormancy during the year. season. After emerging from hiberna- and they present hazards to machinery, During winter months, most ground tion, they feed almost exclusively on pedestrians, and livestock. Burrows squirrels hibernate, but some young green grasses and herbaceous plants. around trees and shrubs can damage can be active at this time, particularly in When annual plants begin to dry and and dry out roots; this can sometimes areas where winters aren’t severe. produce seed, squirrels switch to seeds, topple trees. Burrowing beneath build- During the hottest times of the year, grains, and nuts, and begin to store ings and other structures sometimes most adults go into a period of inactiv- food. produces damage that necessitates ity, called estivation, that can last a few costly repair. Ground squirrels usually forage close days to a week or more. During these to their burrows. Their home range Ground squirrels can harbor diseas- periods, the burrow appears open at typically is within a 75-yard radius of es harmful to humans, particularly the entrance, but the squirrel plugs it their burrow. when squirrel populations are high. with soil near the nest. A major concern is bubonic plague, The onset of breeding in California DAMAGE caused by the bacterium Yersinia pestis ground squirrel populations can vary and transmitted to humans, pets, depending on weather, elevation, and Ground squirrels damage many and other animals by fleas associated latitude. Generally, populations at food-bearing and ornamental plants. with the squirrels. Ground squirrels higher altitudes and in colder climates Particularly vulnerable are grains, as are susceptible to plague, which has hibernate for longer periods and well as nut and fruit trees such as al- wiped out entire colonies. If you find therefore breed later. Mating can start mond, apple, apricot, avocado, orange, unusual numbers of squirrels or other as early as January in warmer locations peach, pistachio, prune, and walnut rodents dead for no apparent reason, and continues until July. Peak mating (Figure 4). notify public health officials.Do not occurs from March through June. In gardens, ground squirrels will eat handle dead squirrels under these circumstances. California ground squirrels only pro- vegetables in the seedling stage. They duce a single litter per year. The average can damage young shrubs, vines, and litter has 5 to 8 young, but litters as trees by gnawing bark, girdling trunks LEGAL STATUS small as 1 and as large as 15 have been (completely removing a strip of bark The California Fish and Game Code observed. The young are born in the from a tree’s outer circumference), classifies ground squirrels as nongame burrow and grow rapidly, emerging eating twigs and leaves, and burrowing mammals. An owner or tenant can from the burrow when they are about around roots. Ground squirrels will control (“take”), in any legal manner, 6 weeks old. At 6 months of age, they gnaw on plastic sprinkler heads and nongame mammals that are injuring resemble adults. irrigation boxes and lines. growing crops or other property. Some Burrowing can be quite destructive. species of tree squirrels, on the other Pest Notes: Ground Squirrel Page 3 of 7 hand, are classified as game animals S. mohavensis, and the San Joaquin rabbit (Sylvilagus bachmani ripari- (with a hunting season) that cannot antelope squirrel, Ammospermophilus us), the riparian wood rat (Neotoma be taken without a permit. See the nelsoni, as threatened species. fuscipes riparia), and some endan- Pest Notes: Tree Squirrels for more Therefore, both are protected animals. gered amphibians and reptiles also are information. Although you are unlikely to mistake within the California ground squirrels’ either of these relatively small squirrels range, so some squirrel management No license is required for the manage- for the much larger California ground techniques could impact them as well. ment of California ground squirrels if squirrel, their ranges could overlap in If the kit fox is found in your county, it is the owner or tenant who is taking some areas, so ensure proper iden- contact your county agricultural com- damaging ground squirrels. A trapping tification before instituting control missioner for additional information. license from the California Department measures. For a range map, see the California of Fish and Wildlife is required for Department of Pesticide Regulation’s those who are trapping squirrels for The endangered San Joaquin kit fox website (listed in References). hire or profit. (Vulpes macrotis mutica), several endangered species of kangaroo rats Before using pesticides for ground The U. S. Fish and Wildlife Service (Dipodomys spp.), the riparian brush squirrel management, read the product classifies the Mohave ground squirrel, Table 1. Seasonal activity, diet, and optimum timing for management of California ground squirrels. Pest Notes: Ground Squirrel Page 4 of 7 Figure 5. A pair of box-type gopher Figure 6. The tunnel-type trap kills Figure 7. A Conibear trap at the base traps modified and set in the runway animals that pass through it. of a structure. To use a Conibear of ground squirrels. trap, dig a slice of soil from the entrance so the trap will fit flush to label to determine if any restrictions California ground squirrels generally the edges of the burrow entrance. exist on rodent control within the rang- dislike dense vegetation, as it prevents es of these and other endangered and their easy detection of potential pred- method of euthanasia and is illegal in protected animals. ators. Therefore, avoiding mowing and California (See References). grazing can discourage ground squirrel MANAGEMENT incidence. Keep in mind, however, that There are several types of traps that kill increasing the amount of vegetation ground squirrels, including box traps, Effective management depends heavily in an area may encourage other pest tunnel traps, and Conibear traps. For upon understanding the unique life species, like California field voles. box traps (Figure 5) and tunnel traps cycle and behavior of the California (Figure 6), place them on the ground ground squirrel. For example, bait- Ground squirrels can reinvade a site by near squirrel burrows or runways, and ing with treated grain is effective in moving into vacant burrows. Although bait them with walnuts, almonds, oats, summer and fall, because squirrels not usually possible in urban areas, barley, melon rinds or any other food primarily feed on seeds during this destroying old burrows by deep ripping source that the ground squirrels are period.