Ariège has an unrivalled wealth of wildlife and many naturalists eager to help you discover it. The Association des Naturalistes de l'Ariège has a regular schedule of tours from late March through October. Every Tuesday and Thursday in July and August a naturalist from the Office National des Forêts leads a tour of the reserve around Mont Valier. You can also hire a guide (or join a scheduled walk s/he has organised) to lead walks in the mountains--most are very knowledgeable about local plant and animal life.
One of the most interesting mammals found only in the Pyrenees is the rare, shy Desman, an aquatic insectivore with a snout resembling an elephant's trunk. If you manage to spot this tiny creature in a river or lake, consider yourself extremely lucky.
Also of interest:
Les Papillons d'Amarante: Cathie and Pascal Proust's tropical garden on the Col del Teil (near Belesta and Puivert) is home to numerous species of butterfly not native to the Pyrenees. Open to the public from late May through September. 05 61 01 98 80
La ferme aux reptiles: Snakes, lizards, turtles and other creeping things. Near la Bastide-de Sérou. Open daily July and August, weekends the rest of the year.