When I was a traffic signal & lighting tech 1973-2004, the squirrels would chew in a perfect circle around the top of the photoelectric cell for the street light, opened 'em up like someone had used an old fashioned can opener leaving the 'lid' sticking up. The rain would come in, mess up the circuity after a time and we'd get a call for the street light dayburning. At least the PEC would fail with the light on. They love polystyrene plastic and thermoplastic wire insulation! Their gopher cousins would burrow into any electrical pull box in the ground that did not have the bottom grouted and gnaw the traffic signal wiring. In 31 years I pulled dozens of their electrocuted carcasses out of pull boxes and repaired the damage, cussin' as I did so! I'm sure they are still carrying on their rodent duty even to this day, 13 years AFTER I retired!