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Twenty-three species and 119 subspecies of ground squirrels exist in the United States (Hall 1981). At least 10 species can be of considerable economic importance to agriculture or have a significant impact on public health. This chapter covers the three species found in the far west and southwest. All three species range over extensive regions. While the California (Spermophilus beecheyi) and the Belding’s (S. beldingi) ground squirrels are considered pests over large agricultural areas, they are not pests throughout their entire range. The rock ground squirrel (S. variegatus) is not a major pest but is important because of its involvement in the spread of plague. The California and rock ground squirrels are closely related, belonging to the same subgenus, Otospermophilus. They are similar in general size and body configuration. The Belding’s ground squirrel, more commonly referred to as just the Belding ground squirrel, is substantially different in appearance from the California and rock squirrels.
Exclusion: Limited usefulness and costly.
Cultural Methods: Flood irrigation and deep tillage may help discourage ground squirrels.
Habitat Modification: Eliminate brush, rock piles, and old unused farm machinery that serve as harborage for the California ground squirrel.
Frightening: None are effective.
Repellents: None are very effective.
Toxicants: Zinc phosphide. Anticoagulants (diphacinone and chlorophacinone). Cholecalciferol (state registration only for rock squirrels).
Fumigants: Aluminum phosphide. Gas cartridges.
Trapping: Box-type traps (kill and live catch). Conibear® traps.
Shooting: Limited effectiveness.
Other Methods: Burrow ripping following control.