Managing Wyoming ground squirrels
by W.F. Andelt, S.N. Hopper* (7/14)
Reviewed by Marvin Reynolds**
- The Wyoming ground squirrel is one of six species of ground squirrels found in Colorado.
- Wyoming ground squirrels compete with livestock for forage and can destroy food crops.
- Wyoming ground squirrel burrowing can damage hay fields, grasslands, golf courses and lawns.
- Wyoming ground squirrels can be controlled by shooting, trapping, poison grain baits and fumigation.
The Wyoming ground squirrel (Spermophilus elegans) is one of six species of ground squirrels found in Colorado. Formerly called “Richardson’s ground squirrel,” the Wyoming ground squirrel averages 10 to 15 inches long and weighs 9 to 14 ounces as an adult. Its fur is generally a brownish smoke-gray, with a dappled pattern of cinnamon-buff. The underside of the tail is buff.
Wyoming ground squirrels are found in Colorado, southern Wyoming, western Nebraska and Utah. The species occupies areas from 5,000 feet to above timberline in the north central and northwestern sections of Colorado. It prefers open sagebrush, grasslands and subalpine meadows.
Ground squirrels are hosts for fleas and may act as carriers for bubonic plague. Plague is transmitted to humans via flea bites. Early symptoms of plague include swollen and tender lymph nodes, chills and fever. Early diagnosis and treatment is imperative. When walking through suspected plague areas, apply an insect repellent to socks and pant cuffs before tucking pants inside boots.
Food Habits and Biology
Wyoming ground squirrels prefer green foliage, such as grasses, but also eat forbs and shrubs. When green vegetation becomes scarce, the squirrels eat dry grasses and seeds. They also eat insects, including grasshoppers, crickets and caterpillars, and scavenge eggs from ground-nesting birds.
Wyoming ground squirrels construct and live in underground burrows. In brushy country, Wyoming ground squirrel burrows often are identified by a substantial pile of debris (sticks, rocks, sagebrush leaves) that covers the area downslope from the burrow entrance. Squirrels stay in their burrows at night and during the warmest part of summer days. The burrow is the center of a ground squirrel’s activity.
The squirrels enter their burrows in late July or early August and hibernate underground until the following March or April. Males usually come above ground one to three weeks before the females. Breeding takes place one to four days after females emerge from hibernation. The young are born after a three- to four-week gestation period with two to 10 young per litter. Only one litter is produced each year. The young are weaned at five weeks and are above ground foraging by June. Density of Wyoming ground squirrel populations can range from two ground squirrels per acre before young are born in the spring, to 20 or more animals per acre in early June when juveniles and adults are active.
Predators include bullsnakes, coyotes, foxes, badgers, weasels and hawks.
High concentrations of Wyoming ground squirrels can pose a serious pest problem. They compete with livestock for forage and can destroy food crops. The mounds of dirt that squirrels excavate to build burrows in hay fields can damage haying equipment and take fields out of production. Burrowing activity also can damage grasslands, golf courses and lawns.
Several alternatives are available for Wyoming ground squirrel control. Landowners may use control methods themselves or hire a commercial firm.
Small, isolated colonies of Wyoming ground squirrels can be effectively controlled by shooting. Shooting lowers the population by removing individuals and disrupting their life cycle. However, if there are other colonies of ground squirrels nearby, individuals from those populations will migrate into the area where squirrels are being removed. For effective control of problem ground squirrels, a population must be kept under constant shooting pressure.
For small populations, wire-mesh cage traps can be set anywhere that squirrels frequent. Place traps on level ground within a few feet of burrows or other high-activity areas. Bait for several days with the door wired open to get squirrels accustomed to visiting the trap and unafraid of it. Wooden snap-type rat traps and modified pocket gopher traps also can be used.
Bait the traps with rolled oats, peanut butter, fruit such as apples, or grain, depending on what works best in your area and the time of year. If corn is used as bait, it should be cracked.
Conibear #110 body traps are useful early in the season when the squirrels have plenty of green forage available and are not easily enticed to baited traps. Set the trap directly over the burrow opening to capture the squirrel as it emerges. The trap should fit directly over the entrance and not allow the squirrel to walk around the edge of the trap.
Poison Grain Bait
|Product labels vary among manufacturers and with time. Carefully follow current label directions.|
Poison grain bait is the most practical method for controlling large numbers of Wyoming ground squirrels. Baiting is most effective at two points during their annual cycle: early spring, or late June to early July.
In a year of average rainfall, begin poison grain control early in the spring, about one to two weeks after squirrels emerge from their burrows. Continue for one month or until vegetation turns green. Early control is enhanced by cold weather and minimal vegetative growth that makes bait more desirable to ground squirrels.
As soon as green vegetation becomes available, bait is less accepted. To achieve successful control in early spring, apply bait when the entire ground squirrel population is active. If part of the population is still hibernating, baiting is not effective. Since females emerge one to two weeks after males, do not start baiting at the first sign of activity. Baiting also is not effective late in the gestation period or shortly after the young are born because females are rarely above ground then. Check the activity level of the population by trapping or shooting 10 or more animals and checking the ratio of males to females. A 1-to-1 ratio usually means that females are active and baiting is appropriate.
Baiting in mid-summer is common in Colorado. Bait after green vegetation is dry and dormant (sometime in June or July) but before squirrels disappear into their burrows to hibernate in late July to early August. Bait acceptance is high in June and July because Wyoming ground squirrels are eating to build fat reserves for winter. In a very dry spring, control can continue from April until July because of the scarcity of green vegetation.
Two percent zinc phosphide is the only legal grain bait for control of Wyoming ground squirrels in Colorado. Bell Laboratories’ ZP Rodent Bait AG, Liphatech’s Ridall-Zinc and Hacco’s Zinc Phosphide Oat Bait and Pellets are 2 percent zinc phosphide baits labeled for use in Colorado. Zinc phosphide baits are labeled for use on rangelands, non-crop areas such as lawns, ornamentals, golf courses, parks and nurseries, and non-crop rights-of-way. Liphatech’s Ridall-Zinc is not registered for use on ornamentals and parks, whereas Bell’s ZP Rodent Bait AG and Hacco’s Zinc Phosphide Oat Bait and Pellets are not registered for use on non-crop rights-of-way.
Prebaiting with untreated, steam-rolled oats, barley or cracked corn (depending on bait used) two to three days before baiting improves bait acceptance. On rangelands, apply prebait and bait by hand in a 6-inch bait spot near each active burrow. Place no more than 1 teaspoon (4 grams) of bait per spot. Do not place bait in the burrows because squirrels forage above ground and are wary of any food found in the burrow. Apply bait only after all or most of the prebait is eaten, and only in areas where prebait is consumed.
In non-crop areas, apply prebait and bait by hand near each active burrow or runway. Place bait (no more than 1 teaspoon per burrow) on the grass and allow it to fall to the ground. Do not put treated bait in piles.
Two percent zinc phosphide manufactured by Liphatech can be broadcast on non-crop rights-of-way. Prebait with rolled oats, barley, or cracked corn at a rate of 4 pounds per acre two to four days prior to baiting. Broadcast bait in 20-foot swaths (this varies depending on the bait being used) using hand or ground-driven equipment. Do not broadcast near homes or water, or on roads.
Zinc phosphide is a slow-acting toxicant that can be absorbed in small amounts through the skin. Wear rubber gloves to avoid contact with the chemical. Take extra care to avoid breathing zinc phosphide dust. Zinc phosphide baits are classified as restricted-use pesticides. This classification means that landowners must obtain private certification from the Environmental Protection Agency before they can purchase or use these products. Obtain certification information from your Colorado State University Extension county office.
Because product labels vary among manufacturers and change with time, carefully follow current product labels. Bell Laboratories’ ZP Rodent Bait AG is approved for use from July through December on rangelands but doesn’t have a seasonal restriction on other areas. Liphatech’s Ridall-Zinc is recommended for use from April through June on rangelands and when broadcast on non-crop rights-of-way. All other uses are permitted year round. Hacco’s Zinc Phosphide Oat Bait and Pellets do not have a seasonal use restriction.
Apply poison bait only once per year. Surviving squirrels from the first treatment sometimes become ill after eating bait. Consequently, these animals will become bait shy and further treatments are unsuccessful.
Use of poison baits according to label directions usually results in an 80 to 90 percent reduction in Wyoming ground squirrel numbers. Poor results after baiting usually are due to improperly placed bait, failure to prebait, presence of green vegetation, or inactivity of a portion of the ground squirrel population.
Diphacinone (Ramik Green), strychnine, and 1080 grain baits are no longer legal for use on Wyoming ground squirrels in Colorado.
Use fumigants when additional control is required. Aluminum phosphide and gas cartridges are registered for use in Colorado. Trade names for aluminum phosphide include Phostoxin, Gastoxin and Fumitoxin. Aluminum phosphide is classified as a restricted use pesticide and gas cartridges are classified for general use. Aluminum phosphide emits a poisonous gas (hydrogen phosphide), whereas gas cartridges produce a suffocating gas primarily composed of carbon monoxide. Fumigants are most effective when used in moist soils in early spring.
Aluminum phosphide is classified as a flammable solid. Transportation of aluminum phosphide by commercial firms is governed by U.S. Department of Transportation rules and regulations. These regulations are subject to change. If you have any questions, call Hazmat (Colorado State Patrol Hazardous Materials Section) at (303) 273-1900.
To use aluminum phosphide, insert one to four tablets (usually one) as far back into the burrow as possible. Then insert a wadded newspaper and plug the opening to the burrow with moist soil or a plug of sod placed grass-side down to form an airtight seal. The wadded newspaper prevents the fumigant from being covered and may delay ground squirrels from digging out before the tablets activate. Aluminum phosphide appears to provide the best control when soil temperatures are above 60 degrees F.
To use the gas cartridge, punch at least five or six holes in one end with a nail or ice pick. Insert the sharp point part way and rotate it to loosen the contents so the cartridge will burn more rapidly. Insert and light the fuse. Once the fuse is burning well, gently slide the cartridge as far back into the burrow opening as possible. Immediately plug the opening with moist soil or a piece of sod placed grass-side down to form an airtight seal. Do not cover or smother the cartridge. As a rule, cartridges do not give satisfactory control if the soil is dry.
The hydrogen phosphide gas produced by aluminum phosphide tablets is toxic to all forms of animal life. Exposure through inhalation produces symptoms such as a pressing sensation in the chest, dizziness, nausea, vomiting and a rapid onset of stupor. Expose affected people to fresh air and provide immediate medical attention.
After Wyoming ground squirrels have been exterminated, reinvasion may be slowed by deep ripping with a tractor and ripping blade. After successful control of California and Belding ground squirrels, 18-inch-deep ripping of individual burrows or the entire area significantly reduced recolonization. Ripping did not reduce ground squirrel numbers on sites where control was unsuccessful. Weigh negative aspects of ripping, such as cost, against the potential benefits of slower recolonization and reduced frequency of rodenticide use.
Source of Supplies
Rodenticides for controlling Wyoming ground squirrels are available through commercial vendors in Denver, a few farm supply stores outside Denver, and the Animal Health Division, Colorado Department of Agriculture, (303) 869-9130. Traps can be purchased or ordered at hardware
stores. Your Colorado State Extension county office may have a list of suppliers.
Place placards on all four sides of vehicle.
Carry shipping papers containing the following information: proper shipping name (aluminum phosphide), hazard class/division number (4.3), material identification number (UN1397), packing group designation (PG 1), subsidiary hazards (poison 6.1 inhalation hazard), and amount of product in quantity and total gross weight.
Keep the aluminum phosphide in the original canister and box.
Keep a log book if transporting aluminum phosphide over 100 air miles. The log book is a record of duty for the day, recorded in 15 minute intervals. If transporting under 100 air miles, only a time record must be kept. This includes name of person transporting, date, time started on duty, and time going off duty.
Carry a fire extinguisher with a rating of 10B:C.
Prior to transporting aluminum phosphide, the driver must be satisfied that the vehicle is in safe operating order. At the end of the day that the material was transported, the driver must prepare a written inspection report. The following parts and accessories should be inspected and reported on: service brakes including trailer brake connections, parking (hand) brake, steering mechanism, lighting devices and reflectors, tires, horn, windshield wipers, rear vision mirrors, coupling devices, wheels and rims, and emergency equipment.
The report should identify the vehicle and list any defects or deficiencies found. If none are found the report should so indicate. Correct any defects or deficiencies before operating the vehicle again and note the corrections in the report. The report should be signed by the driver. Make two copies of the report. Keep one copy in the vehicle until the next time an inspection report is required, and keep one copy at the driver’s place of business for at least three months from the date the report was prepared.
In addition to these pre- and post-trip inspections, a more in-depth annual inspection is required. Information pertaining to this inspection may be obtained by calling Hazmat at (303) 273-1900.
Have $1,000,000 insurance if transporting aluminum phosphide in a vehicle with a greater than 10,000 pound gross vehicle weight rating or if transporting over a state line.
The driver must be over 21 years old.
*W.F. Andelt, Colorado State University professor emeritus, fish, wildlife and conservation biology; S.N. Hopper, consultant.
**Marvin Reynolds, CSU Extension area director, range & natural resources, SLV Area. 8/98. Revised 7/14.
Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.
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Updated Tuesday, August 05, 2014