Wool, fur and feathers consist primarily of keratin which is one of the most indigestible proteins. There are, however, some insects which are adapted for feeding on this diet. Special conditions in their gut enable them to break down the sulphur linkages in the keratin and thus render it digestible.
In the wild insects that can digest keratin probably feed mainly on the remains of animals left by carrion-eaters, but they are also found in nests and lairs containing down or hair. However, keratin alone does not provide a sufficient diet for the normal development of an insect. It lacks, for instance, certain vitamins. In the wild the insect will have plenty of opportunities for supplementing its diet, but this is not possible if it is feeding on a completely clean textile. If it is to thrive it must be able to eat small amounts of food remains or traces of sweat and urine.
In addition to the true specialists there are many animals occurring indoors which occasionally gnaw textiles. This may be because there are stains on the material to which they are attracted, but they may also do so in order to pupate. Mice and rats often cause serious damage by gnawing textiles, particularly in stores and warehouses, when they are gathering nest material.