Early in Michael Hyland's career, when he worked with electric power crews in New Hampshire, word got back to him that a customer was upset after experiencing a series of outages over a short period of time.

"As anyone would be," said Hyland, now senior vice president of engineering services with the American Public Power Association (APPA).

The customer service representative had tried to explain the problem to the man: a little something people in the business call "chew." In other words, squirrels had been chewing through the lines or otherwise interfering with the seamless delivery of electricity.

"He really was mad at us," Hyland remembered. " 'You're lying,' he said. 'I've never seen a squirrel.' "

It seemed inconceivable to the man that such tiny jaws could lead to such big problems. So Hyland set out to convince him.

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"We called out to our crews and said, 'Hey guys, when you're out working, if you get to a site and find a squirrel that's half-burnt, we want you to bring it home and put it in a box.' "

After a few weeks, Hyland's crew went to the man's house, box in hand.

"We visited him with like 27 squirrels, some of which were still smoking," he said.

Hyland was reprimanded, but he had made his point.

"I've been involved in the squirrel war for 30 years," he said.

It's a war that shows no sign of ending any time soon.

The power can go out for many reasons. In the Southwest, high summer heat can cause air-conditioner overloads. In the Southeast, lightning can knock out the lights. (In Key West, Fla., iguanas are a problem.)

In the Midwest to the Mid-Atlantic and into New England, squirrels are "pretty much the number one enemy," Hyland said.

In 2015, the APPA decided to start calculating what it calls the Squirrel Index, asking members to share data on squirrel-related outages. In 2018, the system reported 1.6298 squirrel-related outages for every 1,000 customers.

Extrapolating from that, the association estimates that last year, squirrels caused 244,137 power outages across the nation. Squirrels have been more successful than any cyberterrorist.

How and why do squirrels wreak their havoc?

Start with their teeth. A squirrel's front teeth never stop growing. To keep them from growing through its own head, a squirrel must grind them down by gnawing on hard materials. That includes the high-density polyethylene plastic that covers coaxial and fiber-optic cables and some electric lines.

Tree squirrels, such as Eastern grays, like to be up high.

"They love to run on our overhead lines," Hyland said. "It lets them cross streets and keeps them above their enemies."

Touching one wire usually doesn't spell doom for a squirrel. But touching two can. A squirrel may not appreciate the danger because when it was small, it had no difficulty navigating spaces abuzz with live wires.

"All of a sudden," said Hyland, "the tail grows, it's touching ground or another phase, and to say it pretty simply, they complete the circuit. When that happens: poof!"

The squirrel goes from a furry flying Wallenda to a frying Wallenda.

Lineworkers sometimes photograph the deceased rodents: their tails blackened or their teeth still clenched around the wire that killed them.

Utilities install guards around equipment, trying to keep the squirrels out. Often, workers return to find the guards chewed through. Plastic owls - designed to frighten squirrels - are a temporary fix and end up chewed, too. High-pitched sounds, inaudible to the human ear but supposedly crazy-making to squirrels, can wind up irritating nearby dogs.

"Whatever you seem to do, there's an alternative problem," Hyland said.

The APPA recommends utilities review outage data to see when and where outages occur. "We keep preaching a good vegetation management program," Hyland said. "Keep trees away from lines."

The association has even tried a tongue-in-cheek approach: Last Jan. 21 - Squirrel Appreciation Day - the association published on its website an open letter to squirrels.

"Don't touch, hang out near, or hover above transformers," read the letter in part. "Don't build your nest on electrical equipment . . .

"Think before you chew: Gnawing on lines and other equipment might be soothing on your teeth, but poses a significant danger to you. You don't want a power line to be your last meal!"

Of course, to read the letter, a squirrel would have to have Internet access. But odds are, the power was out.

This article was written by John Kelly, a reporter for The Washington Post.