An unusual family

Four males on a female mite's abdomen

Fig. 85. Four males crawling around on the abdomen of a fertilized female (Rack)

When a water mite – one of the 2mm big ones – is spotted in the microscope, you will see up to several mites at once.

There are both male and female water mites. The fertilized female mite finds an insect larva (or, in the lack of a better host, a human), which she latches onto and then injects the mouth parts into the skin. After a few hours her abdomen swells up and she is sought out by one or more males. The males then spend the rest of their short lives to crawling on large abdomen of the fertilized female. When they get hungry, they inject their mouth parts into the female and suck out nourishment. In the female’s abdomen, the next generation of water mites is developed.

You can clearly see the new mites because the female abdomen is completely transparent. The water mites are born as adults. Often the males help giving birth to the new mites. They cut a hole in the abdomen with their powerful hind legs and pull out the new females for immediate mating. Males only help at the birth of female mites. New males are on their own.

Water mites

Water mites with typical size

Fig. 84. Water mites. A non-engorged female of normal size and body shape. (Rack)

They are not very common, but can be considered as a possible cause of unexplained itching. Ball mites are actually quite small animals that are only 0.2 mm long. The fertilized females may, however, swell and become spherical with a diameter of up to 2 mm.

One of the water mite species is called Pyemotes ventricosus. It lives as a parasite on the skin of moth larvae and beetle larvae. In places where there are many larvae, there can be an excess of hungry water mites. This could be in old hay, or in granaries and other places where there are many insect larvae. Another water mite species live on the deathwatch beetles.

Attacking people
Water mites crawl around in search of a larva, or they move passively through the air with dust. If they end up on a person, they will hang on and try to inject their digestive enzymes into the skin. This results in an itchy, allergic skin reaction, similar to that of fur mite bites. They typically bite the hands, arms and chest. There are known examples of people being exposed to water mites in their workplace who brings them home in the clothes and has infects the rest of the family.

Water mites cannot survive without insect larvae for long periods of time and if they end up on a human they will die after a short period of time. When their mouthparts are injected into the skin, they do not stick very well to the host. A shower will wash them off.

When the water mites have been confirmed by microscopy, control measures should be taken. This is done by combating their host animals – the insect larvae.