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350 South Huntington Avenue, Boston, MA 02130
(617) 522-7400
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Angell Animal Medical Centers – Boston

350 South Huntington Avenue, Boston, MA 02130
(617) 522-7282
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293 Second Avenue, Waltham, MA 02451
(781) 902-8400
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(339) 970-0790
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565 Maple Street, Danvers, MA 01923
(978) 304-4648
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Animal Care and Adoption Centers – Boston

350 South Huntington Avenue, Boston, MA 02130
(617) 522-5055
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Animal Care and Adoption Centers – Cape Cod

1577 Falmouth Road, Centerville, MA 02632
(508) 775-0940
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Animal Care and Adoption Centers – Nevins Farm

400 Broadway, Methuen, MA 01844
(978) 687-7453
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Animal Care and Adoption Centers – Northeast Animal Shelter

347 Highland Ave., Salem, MA 01970
(978) 745-9888
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NOTE: Pesticide Issues/Complaints/Questions can be left on the MDAR Pesticide Division Enforcement phone line at 617-626-1782. This is a recorded line. Please leave a message and an Inspector will return the call. Or if preferred the Complaint Form can be completed and submitted. Please use the following link:

What are rodenticides?

A rodenticide is a pesticide used to kill “pest” animals, such as mice and rats. Rodenticides are problematic not only because they cause immense suffering in target animals, but also because they can sicken and kill non-target wild animals, such as eagles and owls, as well as family pets, including cats and dogs, who eat mice or rats who had ingested the poison. There are several different types and classes of rodenticides, some of which are slightly less inhumane or less dangerous to non-target animals. However, all rodenticides inflict pain and suffering and none are guaranteed to spare non-target animals should they consume it. Learn about our rodenticide bill, which would encourage more humane approaches to rodent control and also help to protect wildlife.

Types of rodenticides

There are currently three classes of rodenticides: first-generation anticoagulants, second generation anticoagulants (SGARs), and acute toxicants. The first two groups — first-and second-generation anticoagulants — are  poisons used for rodent control that work by stopping the blood clotting processes, causing lethal hemorrhage. Animals bleed internally and suffer severe pain for several days before dying. While it’s unclear exactly how long it may take for an animal to die (as it is dependent on the amount consumed), some studies conclude it takes 1-3 days for rats to die, while others have found it takes 4-8 days, and other research shows it can take up to 11 days for mice to die. Animals typically remain conscious until close to the time of death.

Anticoagulants are also the most dangerous to non-target animals (i.e., pets and non-target wildlife). First-generation anticoagulant rodenticides last for approximately 7 days in an animal’s system, but SGARs are more potent and generally last for 4 weeks, making them more dangerous to other animals who ingest poisoned prey. Predators tend to prey on poisoned dying animals due to their inability to move quickly. Animals who eat these poisoned animals (or the poison itself) may die a similarly painful death, or they may survive, but suffer hemorrhaging and detriments to their ability to reproduce, thus having broader population impacts.

The third category, acute toxicants, are considered slightly less cruel and less risky to non-target animals, but they are still dangerous and inflict suffering.

One type of acute toxicant — alpha-chloralose — is relatively easy to treat in non-target animals if discovered quickly, and appears to cause relatively less suffering in rodents. Also, animals who ingest sublethal doses rapidly recover to normal functioning. However, mice can build up a tolerance to alpha-chloralose and therefore carry a large quantity in their bodies that could severely impact non-target animals who eat the mice. And non-target animals must receive treatment quickly if they are to survive.

Another commonly used acute toxicant, zinc phosphate, usually kills the animal who ingests it within a few hours, but it causes severe pain. There is also no antidote to zinc phosphate, making it deadly to non-target animals. A third type, Calciferol, though classified as an acute toxicant, typically takes several days to kill the animal, causing pain and illness during that time. Its effects can be reversed, but with difficulty.

Another type, strychnine, also causes death. In early 2022, two dogs tragically died in Reading, Massachusetts, after ingesting what their veterinarian suspects to be this type of rat poison.

Is rat poison really that dangerous to other wildlife and to pets?

Yes. It usually takes days for a rodent to die from rat poison, during which time non-target species can ingest one or more contaminated animals. Non-target animals can also consume the poison directly.

The impact of rat poison on wildlife has been documented across Massachusetts. A 2011 peer-reviewed study found that 86% of 161 birds of prey, tested at Tufts Wildlife Clinic, had some form of SGARs in their liver tissue. A second study, conducted from 2012-2016 and also utilizing Tufts Wildlife Clinic to test four different species of birds of prey in Massachusetts, found a rate of 96%. Dr. Maureen Murray, researcher at the Tufts Wildlife Clinic at Cummings Veterinary Medical Center at Tufts University, notes that these birds are representative of the state, and that the food chain is extensively contaminated. A 2020 study reports that a stunning 100% of 43 red-tailed hawks in New England who were tested had anticoagulant rodenticide in their bodies, indicating that the presence of rodenticides in our wildlife has only increased over the past decade. In a 2023 article scientists note that “these findings have global implications as increasing concern regarding exposure to and toxicosis from ARs in nontarget wildlife worldwide leads to a search for alternatives and effective mitigation approaches.” And while the rodenticide may not always kill these non-target animals, it can still impact their ability to reproduce and sicken them. Animal control officers and veterinarians in the Commonwealth have seen, for example, birds of prey fall out of trees from muscle weakness and choke on their own blood from internal bleeding as a result of having ingested rodenticide.

The risk is so great to both wildlife and household pets that wildlife organizations have urged homeowners to only use poison as a last resort and, if hiring a pest control company, ask them to use non-SGAR materials. There are many tragic examples Massachusetts of wildlife and pets dying from rat poison — either because they consumed it directly or because they ate a prey animal that had ingested it— including the state’s first confirmed rodenticide-caused eagle death in March 2021, which was followed by another bald eagle only 5 months later, Ruby the Red-Tailed Hawk of Fresh Pond, two family dogs, a family of owls, and a pregnant raccoon and her babies. In February 2023, a beloved eagle in Arlington, who was neshttp://“ with her mate, succumbed to rodenticide poisoning despite tireless efforts of wildlife veterinarians. She is survived by her lifelong mate.

“Year after year we see the devastating effects these poisons have on our local wildlife. Our hospitals provide emergency veterinary care to hundreds of animals annually who are suffering from the effects of SGAR’s, and we know there are thousands more that never make it in for treatment. The health of our ecosystem and communities depend on the services these predators provide. It is time to empower people to make better choices when it comes to rodent control.” —Zak Mertz, Executive Director of the Birdsey Cape Wildlife Center

The MSPCA’s Angell Animal Medical Centers alone see dozens of cases of companion animals poisonings each year. The cases peak during spring and fall, when landlords and homeowners are most affected by the presence of mice or rats. The cost of veterinary care to treat an animal who has ingested rat poison can exceed $2,000 and treatment can require weeks of supportive care and medication, putting a significant financial and emotional strain on families.

The MSPCA is currently conducting a survey of licensed Massachusetts wildlife rehabilitators, and the preliminary results are striking. In 2019 and 2020, roughly a third of respondents treated animals that had been poisoned by rodenticide, and about another third treated animals that they suspected had been poisoned. Rehabilitators treated hawks, owls, chipmunks, skunks, and more; half of these animals had been afflicted after consuming a poisoned prey animal, 33% ate the poison directly, and in the remaining 17% of cases, the poison source was not determined. Many of these animals needed to be humanely euthanized. Much work remains to be done in educating the public, as rehabilitators report that they are seeing an increase in rodenticide poisoning cases.

To address this serious issue, legislation has been filed at the Massachusetts State House. S. 487/H. 825: An Act relative to pesticides was filed by State Senator Paul Feeney and State Representative Jim Hawkins in 2023. While personal use of SGARs is already banned in Massachusetts, licensed pest companies can still use it when hired to deal with rodent problems. This bill requires digitization of pesticide use forms for better monitoring and requires the increased use of Integrated Pest Management (IPM) strategies in Massachusetts. We hope educating home and business owners about the dangers of rodenticide will reduce their use in our communities.

What is the alternative?

As with virtually all wildlife conflicts, prevention is the best solution. While rodenticides may kill rodents, they do not solve rodent problems, as they merely create vacant habitat for new animals to fill. Trapping mice and rats is an endless cycle if the habitat is not altered, and so it is critical to address the source of the problem via prevention. Rather than turning to rodenticides, leaders, business owners, homeowners, etc. should adopt IPM, an approach used to solve issues with “pests” while minimizing risks to people, wildlife, and the environment. IPM involves establishing site-specific goals, consensus building, and human behavior change. Using an adaptive management approach, project results are evaluated and revisited if goals are not met.

More specifically, Massachusetts entities should do the following: remove from the problem area all nesting materials, such as old clothing, books, boxes, and papers; remove all food debris and store food in secure containers; and moisten rags with peppermint oil and place them under sinks, cabinets, and in cracks. After all the rats and/or mice have left, seal all holes as small as a dime with quick drying cement, foam insulation, or wire mesh, and attach rubber or metal runners at the bottom of all doors. If traps must be used, choose the Havahart live trap. Use the MSPCA’s Intruder Excluder for more solutions and consult with one of these humane exclusion businesses.

How can I help?

As an individual, there are many things you can do. Choose prevention instead of rat poison in and around your home. If you live in a multi-unit complex, encourage the building manager to do the same. You can also educate others in your community. And keep an eye out for bills like the one mentioned above, S. 487/H. 825: An Act relative to pesticides, for which you can lobby on the state level.

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