Acari (mites)

Order Acari (mites), an overview

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.

Tyrophagus casei, the cheese mite On the right is the cheese mite. It is one of the commonest mites found on food. Although its common name is the cheese mite it can also be found on flour and products containing flour. A ripe, old cheese which is infested with mites will appear to be covered in a grey powder. This consists of live mites, their moulted skins, and their faeces. And if that were not enough the cheese mite can also cause dermatitis in humans.

Glycyphagus domesticus House mite or Furniture mite

On the left is the house mite. The male measures 0.32 - 0.40 mm long, and the female 0.40 - 0.75 mm long.

The eggs take around 5 days to hatch into the typical 6-legged mite larvae. These feed for 2 days, rest for 2 more, then moult.

The next stage feeds for 4 days, rests for 2 , then moults. The next 5 days are active, then 2 resting days, then a final moult into adulthood.

If conditions turn nasty some can go into a resting stage, and will not wake up until conditions become more favourable. This prolonged resting period can be as long as 6 months.

These mites are found in food, furniture, and anywhere that is damp and badly ventilated. In these conditions they often feed on fungi.

Trombicula autumnalis, the Harvest mite, Cotswold mite, Berry-bug

On the right is the harvest mite. In spring the female lays her eggs in the soil or on the surface.

The 6-legged larva hatches several weeks later. The larva varies in colour from orange to red. It ranges in size from 0.22 - 0.60 mm long when fully fed. The larva climbs up vegetation and passes on to any warm-blooded animal that passes by.

After a blood meal, which takes 2- 3 days, it drops to the ground. However if the soil it drops on to is not of the right texture and moisture it dies. If the ground is suitable it moults, but stays inside the moulted skin.

After a time the 8 legged hairy red mite emerges to feed on soil animals or their eggs, and after another moult the adult mite emerges.

The itching caused by feeding can lead to sleepless nights. The mite can survive weeks without feeding.