A Prickly Problem: How to Get Along with our Friend, the Porcupine

By Leslie Anthony.

Many Aprils ago, I was awakened at an ungodly hour by a hellish cacophony. The dog stood on the bed howling, audible curses emanated from several sleeping forms around the house, and from outside came the regular and hollow rasp of what sounded like someone sawing into our beloved Haliburton cottage. Fearing who knows what, I instinctively grabbed an axe, flipped on the outside floods and cautiously opened the front door. There on the porch, oblivious to the light and the swearing—even to the dog whose head now extruded between my legs—sat an enormous, metre-long porcupine, its long, curved claws hooked into the half-log wall as it methodically planed the lower tiers with yellowed teeth. Glancing up only briefly to acknowledge the unwelcome interruption, it calmly returned to the task of ingesting the cabin that had been in our family for generations. Shoving the dog back inside behind me, I’d closed the door and—maintaining proper person-to-quill distance—gently tossed a boot toward what was obviously a full-grown specimen of Canada’s second-largest rodent next to the beaver. That proved enough to dissuade it, and the short-legged, heavy bodied animal waddled off into the darkness.


Baby Porcupine (Erethizon dorsatum) Sniffs at Branch - captive animal
Baby porcupine (Erethizon dorsatum).


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The sight we faced next morning has greeted many a horrified cottager opening up their cabin in the spring: the unmistakable tooth-trails of Erethizon dorsatum had lain bare the underlying wood along much of the outside wall to a height of 60 cm, as well as up and down the wooden post supporting the porch roof. The mess would require extensive sanding and refinishing to rectify, but it was small consolation to know that had we not been on hand the previous evening, the creature may have returned again and again until it had exhausted all accessible gnawing opportunities. What could be responsible for the decidedly un-endearing behaviour of this otherwise endearing forest denizen? I had to find out. Those being the days before Google, I had consulted with colleagues in the Department of Mammalogy at the Royal Ontario Museum, where I was a graduate student in Herpetology at the time.

What I found out was surprising, but also made abundant sense. Like deer, porcupines are browsers, feeding almost exclusively on buds, shoots, twigs, and the inner bark of trees, all of which have a high oil content. Also like deer and other herbivores, porcupines love and actively seek out salt sources; when a stash is found, it’s usually mined repeatedly over time. Coincidentally, many wood preservatives contain high concentrations of both tree oils and mineral salts, so wooden structures treated with these represent easy treats for our spiky friends—particularly in late winter and early spring when all that’s left to eat in the forest are conifer needles and bark. Untreated woods like cedar which contain high concentrations of natural preservatives are also targets.

Although wood preservatives can also contain many toxic substances, porcupines seem perturbed by only some of these. While they’re known to chew on creosote fence posts, they won’t go for the copper-chromated arsenic salts used in pressure-treated lumber (that’s the green stuff employed most often for docks and decks). Porcupines might not realize that there isn’t much nutritive value in cottages, but they are tenacious when they find something they like—which also explains freakish reports of these animals gnawing on the starter-cords of outboard motors, tool handles (likely salty from human sweat), and the exposed radiator hoses of cars on which road salt accumulates over the winter.


Baby Porcupine (Erethizon dorsatum) Stands on Branch - captive animal
Baby porcupine (Erethizon dorsatum).


Fair enough, but what can be done to prevent porcupines from foraging on your cabin if a problem arises? Some people sprinkle moth balls around “appetizing” wooden structures as a deterrent, but the naphthalene from which these are made is hazardous to all forms of life (including, BTW, humans) and isn’t something you want lingering in the soil around a cottage. In addition, mothball vapours are mostly ineffective outdoors, where they’re far too weak to bother a hungry or determined animal.

A good organic alternative would be to employ a liberal sprinkling of cayenne pepper on the wood surface or painted on in a strong water solution. A drawback of this measure is that it has to be replaced after every rain, and so while good for solving an acute problem when you’re not around, cannot be counted on to work over the course of a winter or early spring. Random noise can make life uncomfortable for porcupines; unfortunately it will have a similar effect on your neighbour. One sure solution is to encircle your buildings with unsupported chicken wire that porcupines are too heavy to climb. You can also try a distraction method like placing a large salt block on your property a good distance from a building—though this will also attract all manner of other animals, some of which may be even more unwelcome.

Otherwise, just hope there’s plenty to eat for porkies in the winter forest near your cabin—and keep an old boot by the door in case one gets the springtime munchies.