The sense of smell is not nearly so well developed in man as it is in most other mammals, but there are occasions when even man’s olfactory apparatus is of some use to him.

This applies particularly in the case of foods. We are, for instance, very sensitive to the smell of decomposing food, but certain live animals also leave traces of scent.

Flour mites in flour or grain impart a sweet, sickly smell to these foodstuffs, while the beetle Tribolium destructor produces a substance with a smell like Lysol, and this will be particularly noticeable when infested goods have been kept in tight-fitting containers.

Cockroaches have a characteristic sweet smell, but there has to be several of them before this is apparent, and normally they will already have revealed their presence in some other way.

Most bugs produce a rather unpleasant smell. This comes from a secretion produced by special stink glands on the underside of the thorax, and a room housing several bed bugs will often have a close, sickly smell.

The jet black ant (Acanthomyops fuliginosus) which frequently builds nests in timber produces a not unpleasant, pungent aromatic smell, which sometimes enables one to find the nest by scent. Otherwise the insect pests of timber do not appear to have any characteristic smell, but the close, stuffy smell of mould in a house is an indication of damp.

Many carnivores produce an acrid smell and this will have been apparent to anyone who has crossed the tracks of a marten is a not uncommon visitor to the lofts of houses in the country and these produce a secretion from glands at the base of the tail, which has a typical carnivore smell. The marten produces this secretion when frightened, in exactly the same way as a skunk, and it serves as a scent marking, for these animals communicate with each other by scent.

It is a curious fact that the rank carnivore smell in a house has in some cases been found to come from lamp fittings made of Bakelite, which owing to a fault in the manufacture give off a sharp smell when the fitting becomes warm.

Scent marking can also be carried out by urine and faeces, which often have a characteristic smell. This happens, for example, in the case of rats and mice.

The smell of decomposition in a house can nearly always be traced to a dead mouse or rat underneath the floor and this often occurs after poison has been used.