Ground squirrel poisons fall into two main categories: anticoagulant baits that require multiple feedings over several days, and acute toxicants like zinc phosphide that kill after a single feeding. Both are classified as restricted-use pesticides in most states, meaning you need a permit from your county agricultural commissioner before you can purchase or apply them. Understanding how each type works, and the real risks they pose to pets and wildlife, is essential before choosing a control method.
Types of Ground Squirrel Poison
The most commonly used ground squirrel poisons break down into two groups based on how they kill.
Anticoagulant baits contain active ingredients like chlorophacinone or diphacinone at very low concentrations (typically 0.01%). These work by blocking the body’s ability to clot blood. A squirrel must feed on the bait multiple times over several days before consuming a lethal dose. Standard label directions call for four applications of bait spread roughly 48 hours apart, maintaining a continuous supply over 6 to 8 days so every squirrel in the colony has a chance to eat enough. Research from UC Davis found that the average time to death after the first bait application was 9 days, though individual squirrels died anywhere from 3 to 29 days after exposure. The average mortality rate in controlled studies was about 66%, meaning a third of the population typically survives.
Zinc phosphide is an acute toxicant, a fast-acting poison that kills ground squirrels after a single feeding. When a squirrel eats zinc phosphide bait, stomach acid reacts with the compound to release a toxic gas that is absorbed into the bloodstream. Because it works in one dose, zinc phosphide can reduce squirrel numbers much faster than anticoagulants. The tradeoff is that squirrels are more likely to avoid it. Zinc phosphide has a strong, unpleasant taste, so prebaiting (putting out untreated grain first to get squirrels comfortable eating from that spot) is often necessary before switching to the poisoned bait.
How Anticoagulant Baits Are Applied
Anticoagulant baits can be placed in bait stations, applied as spot treatments near individual burrow entrances, or broadcast over larger infested areas. Each method has different implications for safety and effectiveness.
Bait stations are the safest option for areas where pets, livestock, or children might be present. The enclosed stations allow squirrels to enter and feed while keeping larger animals out. Spot treatments near burrows concentrate bait where squirrels are most active but leave it exposed on the ground. Broadcasting covers the most ground but creates the highest risk of nontarget exposure.
Regardless of method, never pile bait on the ground. Piles increase the hazard to livestock and nontarget wildlife. Pick up any bait that spills, and replace bait that gets wet or moldy, since degraded bait loses effectiveness and squirrels will ignore it. Once feeding stops and you no longer see squirrel activity, remove and properly dispose of all unused bait.
Timing matters more than most people realize. While labels recommend no more than 48 hours between bait applications, laboratory studies on California ground squirrels suggest that just two applications spaced 3 to 5 days apart can achieve similar results. The key is ensuring squirrels consume enough total bait, not that feedings happen in rapid succession.
Risks to Pets, Raptors, and Other Wildlife
Secondary poisoning is the biggest concern with any ground squirrel bait. When a predator or scavenger eats a poisoned squirrel, it can ingest enough toxicant to become sick or die. The level of risk depends on which poison was used and which parts of the carcass are consumed.
Research on hawk nestlings fed strychnine-poisoned ground squirrels found that most of the toxicant concentrates in the digestive tract. Hawks typically gut their prey before feeding it to nestlings. In one study, 70% of ground squirrel carcasses found in ferruginous hawk nests had been eviscerated (organs removed). Of 52 nestlings that consumed poisoned squirrels, 49 survived, with no detectable difference in growth rates compared to nestlings fed clean prey. Three nestlings may have died from secondary poisoning, likely from consuming the gut contents. The pattern holds for coyotes too: in one study, coyotes rejected the viscera of strychnine-poisoned squirrels 66% of the time, though one coyote still died.
Dogs are at higher risk because they tend to eat carcasses whole, guts and all. At least one documented case involved a landowner’s dog dying after eating ground squirrels from a treated area. Cats face similar dangers. If you use any ground squirrel poison, keeping pets away from treated areas is not optional.
If a Pet Eats Poisoned Bait or a Poisoned Squirrel
Anticoagulant poisoning in dogs and cats is treatable if caught early. The antidote is vitamin K1, which restores the blood’s ability to clot. Treatment typically begins with injections, then transitions to oral vitamin K1 given twice daily. For longer-acting anticoagulants like diphacinone, treatment can last six weeks or more, with the dose gradually tapered to prevent relapse. Signs of anticoagulant poisoning in pets include lethargy, pale gums, bloody urine or stool, and unexplained bruising. These symptoms can take several days to appear. If your pet has had any possible exposure, bring the bait packaging to your veterinarian so they can identify the active ingredient.
Fumigants as an Alternative
Fumigation kills ground squirrels inside their burrows using toxic or oxygen-displacing gases. Common options include gas cartridges (which produce carbon monoxide and carbon dioxide when ignited), aluminum phosphide tablets (which release phosphine gas on contact with moisture), and carbon monoxide machines that pump exhaust directly into the burrow system. Aluminum phosphide is extremely dangerous to handle and is also a restricted-use pesticide. Gas cartridges are more widely available and easier to use but less effective in sandy or rocky soils where gas escapes through loose burrow walls.
Fumigation works best in spring when soil moisture is high and helps seal gas inside the burrow system. It also avoids the secondary poisoning problem entirely, since no toxic bait remains above ground for other animals to find. The main limitation is labor: each burrow entrance must be treated and sealed individually, which is impractical for large infestations covering many acres.
Carcass Disposal and Cleanup
After any baiting program, collect dead squirrels as soon as you find them. Every carcass left on the surface is a potential source of secondary poisoning for dogs, cats, hawks, eagles, and coyotes. Bury carcasses deep enough to discourage scavengers from digging them up. Do not handle dead animals with bare hands; use gloves or a shovel.
Remove all remaining bait once you stop seeing squirrel activity. Leftover bait degrades over time but remains toxic long enough to poison birds, rabbits, or other animals that encounter it. Store unused product in its original container, and follow your county’s disposal guidelines for pesticide waste.
Legal Requirements for Purchase and Use
Chlorophacinone, diphacinone, zinc phosphide, and aluminum phosphide are all restricted-use pesticides. You cannot buy them over the counter. In California and most other western states, you need a permit from your county agricultural commissioner, which typically requires completing a pesticide safety training or demonstrating a qualifying agricultural need. Some counties offer subsidized bait programs where the commissioner’s office provides treated grain directly to ranchers and farmers at reduced cost.
Over-the-counter rodenticides sold at hardware stores generally contain second-generation anticoagulants like bromethalin or bromadiolone. These are labeled for rats and mice, not ground squirrels, and using them off-label is both illegal and less effective. Ground squirrels are larger, live outdoors, and have different feeding behaviors than house rodents, so products designed for indoor pest control are a poor fit.