Ground squirrels inhabit most agricultural and rural areas of California. They are found around buildings, gardens, and industrial sites, as well as in nature. Ground squirrels damage many food-bearing and ornamental plants. Particularly vulnerable are all types of grains, and fruits and nuts such as almonds, apples, apricots, peaches, pistachios, prunes, oranges, tomatoes, and walnuts. Ground squirrels eat certain vegetables and field crops at seedling stage. Squirrels damage young shrubs, vines, and trees by gnawing bark, girdling trunks, eating twigs and leaves, and burrowing around roots. Squirrels even gnaw surface-type plastic irrigation pipe.

While burrowing, ground squirrels can also be quite destructive. In the process of digging burrows, ground squirrels make large mounds of soil and rock that may bury and kill grass or other small plants. Burrows and mounds make it difficult to mow and harvest, and present hazards to machinery. Ground squirrels frequently burrow around trees and shrubs, damaging the root systems and sometimes killing the plants. Burrows beneath buildings and other man-made structures sometimes necessitate repair or replacement.

Ground squirrels can transmit diseases (such as tularemia and plague) to humans, particularly when squirrel populations are dense. Do not handle dead squirrels. If you notice unusual numbers of dead squirrels or other rodents, notify public health officials.

Ground squirrels live in a wide variety of natural habitats, but populations may be particularly dense in areas disturbed by humans such as road or ditch banks, fence rows, around buildings, and in or bordering many crops. They usually avoid thick chaparral, dense woods, and wet areas. They live in colonies of 2 to 20 or more animals. Much of their time is spent under ground in burrows where they sleep, rest, rear young, store some food, and escape danger.

Ground squirrels are active during the day and are easily seen, especially in warm weather from spring to fall. During winter months, most ground squirrels hibernate, but it is common for some young to remain active, especially in areas where winters are not severe. Most adults go into a summer hibernation (estivation) during the hottest times of the year.

Ground squirrels reproduce once a year in early spring. Litter sizes vary, but seven to eight young are average. The young remain in the burrow about 6 weeks before they emerge.

Ground squirrels are primarily vegetarians. During early spring, they consume green vegetation such as grasses and forbs. When the vegetation begins to dry, squirrels eat seeds, grains, and nuts, and begin to store food. Squirrels eat fruits and vegetables and are known to eat or gnaw bark from bushes and trees.

Ground squirrels are classified as nongame mammals by the California Fish and Game Code. If you find ground squirrels to be injuring growing crops or other property of which you are the owner or tenant, you may take (control) the squirrels in any manner. You must satisfy special provisions of the California Fish and Game Code if you wish to use leg-hold, steel-jawed traps.

Ground squirrels should not be confused with tree squirrels, which are classified as game animals. Although ground squirrels can climb trees, the two species can usually be distinguished by their response to danger. Frightened ground squirrels retreat to a burrow; tree squirrels climb a tree or high structure.

Traps are practical devices for controlling ground squirrels in small areas where the number of squirrels is moderate. Live-catch traps are effective, but present the problems of how to kill the live squirrels and where to dispose of them. Because ground squirrels carry disease and are agricultural pests, it is illegal to release them elsewhere.

There are several types of traps that kill ground squirrels. Most types work best if you place them on the ground near squirrel burrows or runways. Walnuts, almonds, oats, barley, and melon rinds are attractive trap baits. Place bait well behind the trigger or tied to it. Bait the traps but do not set them for several days so the squirrels become accustomed to them. After the squirrels are used to taking the bait, rebait and set the traps

Ground squirrels can be killed in their burrows by several types of toxic gases, some of which require a special permit from the County Agricultural Commissioner. Fumigation should not be used beneath buildings. It is most effective in the spring or at other times when soil moisture is high. At those times, gas is contained within the burrow system and does not diffuse into small cracks which are often present in dry soil.

Ground squirrel burrows are quite large and can have several entrances. Treat all entrances and then seal them. Fumigation is not effective during periods of hibernation or estivation because the squirrel plugs its burrow with soil. The plug is not obvious to a person examining the burrow entrance.

Toxic baits have long been used for controlling ground squirrels. Some toxic baits are available over the counter and other require a permit for their use that the County Agricultural Commissioner issues. In general, baits requiring a permit are not used by gardeners. When you use toxic bait or any other rodent-control materials, follow label instructions carefully. Anticoagulant baits are recommended for controlling ground squirrels because they are effective against the pest and relatively safe to humans and pets. Anticoagulants interfere with an animal's blood-clotting mechanisms, eventually leading to death. They are effective only when consumed in several feedings over a period of 5 or more days. Effectiveness is greatly reduced if 48 hours or more elapse between feedings. These features, as well as an effective antidote (vitamin K), make the use of anticoagulant baits relatively safe.

Anticoagulant baits can be used in two ways: in bait boxes or by repeated spot baiting. Bait boxes are small structures that the squirrel must enter to eat the bait. Boxes contain sufficient bait for repeated feedings and help keep children and pets from reaching the bait. Bait boxes are the preferred baiting method around homes and other areas where children, pets, and poultry are present. Unless a bait label specifies otherwise, bait boxes can be constructed from any durable material and in a variety of designs.

Anticoagulant baits have the same effect on nearly all warm-blooded animals, including birds. Cereal baits are attractive to some dogs as well as to other nontarget animals, so take care to prevent their access to the bait. Danger to children and pets can be reduced by placing bait out of their reach, as in a bait box. Dead ground squirrels should be buried or discarded in plastic bags. Do not handle them with your bare hands. In case a person or pet ingests anticoagulant bait, contact a physician or veterinarian immediately.

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