County Broadband in Norfolk, England, recently lost service to 442 customers over a weekend when rats chewed through fiber and caused an outage during a snowstorm. The ISP battled bad weather conditions, so it took a few days to replace almost 2,000 feet of damaged fiber cable. The ISP stayed in contact with customers by text and was apologetic that the snow had caused its call center to close on Sunday.

There was a great quote in the press, “Rats are also notoriously difficult vermin to stop, like mini tanks with teeth that often seem able to cut through almost anything . . . even concrete.”

I’ve never heard of a rat problem with fiber in the U.S., although it seems likely that it happens. Judging by the conversations I’ve had with ISPs, and the occasional news article, the primary animal damage to fiber in this country comes from squirrels and gophers.

Squirrels seem to be the primary culprit for animal damage to aerial fiber. Squirrels seem to mainly chew on cables as a way to sharpen their teeth. Squirrel teeth grow up to 8 inches per year, and if squirrels aren’t wearing their teeth down from their diet, they look for other things to chew. There has been speculation that squirrels prefer fiber to other types of cables due to some oil or compound used in the fiber manufacturing process that attracts them.

Years ago, Level 3, a major middle-mile fiber network owner, said that 17% of its aerial fiber outages nationwide were caused by squirrels, with the rest, I assume, from storm damage, auto accidents, and gunshot damage.

Companies use a wide variety of techniques to try to protect from squirrel damage, but anybody who has tried to protect a bird feeder from squirrels knows how persistent they can be. One deterrent is to use hardened cables that are a challenge for squirrels to chew through. However, there have been reported cases where squirrels partially chew through hardened cables, which then lets in water that can cause future damage.

A more common solution is adding a barrier to keep squirrels away from the cable. There are barrier devices that can be mounted on the pole to block squirrels from moving higher. There are also barriers that are mounted where cables meet a pole to keep the squirrels away from the fiber. A few companies have tried more exotic solutions, like deploying ultrasonic blasters to drive squirrels away from fiber.

The most common animal damage to buried fiber comes from gophers. Gophers also seem to like chewing on fiber to sharpen their teeth. There are thirteen species of pocket gophers in the country that range from 5 to 13 inches in length. The two parts of the country with the most pocket gophers are the Midwest plains and the Southwest. Gophers mostly live on roots or on plants they pull down through the soil.

Pocket gophers can cause considerable damage to fiber. These rodents will chew almost anything, and there have been reported outages from gophers that have chewed through buried gas, water, and electric lines. Gophers typically live 6 and 12 inches below the surface and are a particular threat to buried drops.

There are several ways to protect against gophers. The best protection is to bury fiber deep enough to be out of gopher range, but that can add a lot of cost to buried drops. I have a few clients who bore drops and install the fiber in conduit  rather than trench or vibrate the drops directly. Another strategy is to enclose the fiber in a sheath over 3 inches in diameter, which is supposedly too big for a gopher to bite. Another solution is to surround the buried fiber with 6 – 8 inches of gravel of at least 1-inch size – anything smaller gets pushed aside by gophers. These solutions are all expensive, and most ISPs just live with drop cuts.