I’ve noticed many squirrels, especially around U of T and Queen’s Park, with large bald areas

You’re probably seeing one of two things. Female squirrels, when they’re about to have babies, line their nests by tearing out chunks of their own hair. (Human mothers might understand this feeling.) So if it’s spring or summer—birthing season—and the animals you see are missing hair from around their shoulders, you’re probably seeing a homemaking rodent. The other possibility is more distasteful: a patchy squirrel might be suffering from sarcoptic mange, caused by burrowing mites (look for baldness around the head and feverish scratching). Not only does the disease cause a squirrel’s fur to fall out in hunks, leaving it vulnerable to hypothermia, it makes the animal rub itself raw, leaving it open to infection. (Similar mites make themselves at home on other animals, especially dogs.) Mange is highly contagious, but it can be treated. If you have a mangy beast loitering around the house, you can contact the Toronto Wildlife Centre, who will try to trap the animal and get rid of the mites—before you find yourself with a whole backyard full of bald, itchy, ill-tempered, bushy-tailed creatures.