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How Animals Impact Our Electrical Infrastructure

While weather remains the leading cause of power outages, animals ranging from birds to squirrels are responsible for electrical service interruptions each year.
squirrel on electric wire against sunset sky

When you think about power outages, what first comes to mind? The heavy, wet snow of a winter nor’easter? Trees toppled onto power lines during a September hurricane? You might be surprised to learn that animals are responsible for thousands of outages – and millions of dollars in outage-related damage – each year. In fact, a weasel-like animal called a marten once cut off power to the $7 billion Swiss Large Hadron Collider by chewing through a wire.

From birds and squirrels to raccoons and foxes – and even snakes – animals are curious creatures that can find electrical equipment intriguing. Some use power lines for transportation, and some are drawn to the warmth electrical equipment provides. This can lead to substantial equipment damage and lengthy interruptions in power. Read on to learn more about what Unitil and other utilities and organizations are doing to protect the infrastructure consumers rely on – and the animals themselves.

In 1987, a squirrel shut down the Nasdaq stock exchange for 82 minutes.

Squirrels are the animal most often associated with power outages, as they use electrical power lines both for travel and a place to rest. When a squirrel climbs onto an electrical transformer, it may cross the bare wire that leads from the high-voltage line to the transformer. If it were to simultaneously touch this wire and a part of the transformer with sufficient electrical ground, an electrical short can cause both a power outage and the electrocution of the animal. We regularly install two types of specialized guards on our electrical equipment to deter wildlife contact and increase reliability. That way, we protect your power — and those cute critters.

Because animals are most active in the fall and spring, 48% of outages caused by squirrels and other wildlife occur during the months of May, June, and October. On average, our furry squirrel pals cause 8.5% of all annual outages in Unitil’s service territory! Studies show that the installation of 'critter guards' on pole-mounted transformers can reduce animal damage by as much as 78%. While redundancies built into the modern grid make it more resilient, tree-trimming also goes a long way toward preventing animal interference with the delivery of electricity to your home or business.

Unitil does everything possible to keep wildlife safe, and you can make a difference, too! By setting feeders away from power lines and waiting to clear dead trees — common homes for baby squirrels — until summer, you can help avoid some shocking encounters. And if you see a nest close to electrical equipment, please give us a call. (Your animal friends will thank you!)


  • While weather is the leading cause of power outages, squirrels alone are responsible for an average of 8.5% of service interruptions within Unitil's service area annually.
  • Most outages caused by animals occur in the fall and spring, when critters are most active.
  • The installation of “critter guards” goes a long way toward protecting our electrical infrastructure and the wildlife that calls New England home.