Order Acari (mites)

Mites. Over 30 000 species have been described so far. These are medically and economically very important animals as they can transmit or cause disease in both plants and animals, e.g., scabies and mange. They tend to be only a few millimetres long. Most have four pairs of legs, but larvae have only three pairs.

The follicle mites are highly specialised and live in the hair follicles and sebaceous glands of mammals including man. The body is soft and long and the legs have become attachment organs. Demodex folliculorum is commonly found in man, and though it is not believed to cause any disease, it is associated with certain skin disorders, e.g. black-heads, acne and impetigo. Demodex canis (right) is found in dogs. The life cycle is usually completed in around two weeks. After mating the female lays eggs in a sebaceous gland. Then she climbs to the top of the follicle and dies. This block the entrance to the hair follicle and so stops another female entering to lay eggs.

Above is Cheyletus sp. a hunting mite. This mite hunts down and kills pest mites such as dust mites and flour mites. It is often found on bedroom floors, and even in bird's nests. It can cause allergies in some people. Chelytus eruditus feeds on other mites and their eggs. The males are rarely seen, and so females are usually parthenogenic. The female lays her eggs in a small pile of 20 - 30 and broods them. Even after the larvae have hatched she still stays nearby. On hatching the larvae, as is common in mites, have just 6 legs. It is only after they have moulted that they have 8 legs. The whole lifecycle takes 7 or 8 weeks.

Below is Acarus siro, previously known as Tyroglyphus farinae, the flour mite. The male is 0.32 - 0.40 mm long, the female is 0.35 - 0.65 mm long. Its life cycle is similar to the House mite (see below). It is found in any type of flour or seeds, and is a serious pest of stored food. The female can lay 500 - 800 eggs in her life time, at a rate of 20 - 30 per day. To test if flour is infected just spread some on a flat surface indoors and leave for 20 - 30 minutes. When you return if the flour is infected the surface will have become uneven due to the movement of the mites. In large numbers it can cause dermatitis if handled.

On the left is Humerobates sp., a beetle mite. It is a soil-enriching mite.

Below is Tyrophagus sp. a forage mite. This mite infests and spoils food. It can cause allergies in humans, cats and dogs.