Welsh Journals

The Acari R. Turk and C. J. Meechan The mite was the subject of a major exhibition at the Main Building of the National Museum of Wales in 1985. It will be presented at Oriel Eryri, Llanberis in 1986. The title was 'The Mite-y-Monster'; the centrepiece a model of the house dust mite enlarged 3,500 times its natural size. The Acari, commonly known as mites and ticks, form an important part of the arthropodan class Arachnida which also includes such animals as spiders, scorpions and harvestmen. Mites are distributed worldwide, colonising both terrestrial and aquatic habitats. They live in soil and fresh water, in organic debris of all kinds, and on plants and animals, including humans. Mites are among the dominant animals in pastures and arable soils. In forests they greatly outnumber all other arthropods. Some species are known to occur in very hostile habitats such as caves and thermal springs. Unlike other Arachnida, many mites live in close association with other animals as commensals, predators and parasites, some even invade the internal organs of vertebrates and invertebrates. Mites are of considerable economic importance as they can cause great damage to livestock and food products. Yet as detritivores in the soil they are essential to the reduction of organic matter such as leaf litter, thereby adding to soil fertility. More than 10,000 species of mites are known, about half of which live in soil displaying a great variety in forms often combined with a high population density. Their size ranges from 0. to 16 mm. Mites and ticks have been recognised for a long time and always attracted considerable interest because of their small size and remarkable habits. In Egypt, men were aware of mites as early as 1500 B.C. and early Greek writers mention mites and ticks. The Latin name, Acari, derives from the Greek akares, meaning "tiny". By the time of Linnaeus (mid 18th century) about 90 species had been discussed in the literature. In the late 19th and early 20th centuries the development of ever more powerful and refined microscopic techniques helped acarology to rise as a modern science in Europe. By the middle of the 20th century some 1,700 species of mites were recorded for the British Isles. Among the more recent research, important contributions were made by the Welsh acarologist Don R. Arthur. With acarology being a relatively young science, many new species from all parts of the world are discovered each year and ever more insight is gained into their biology, ecology and behaviour. A range of characteristic features distinguishes the Arachnida in general and mites in particular from insects with which they often get confused. In an insect, the body is divided into three main regions (head-thorax-segmented abdomen): in a mite, these distinctions cannot be determined and in most cases there is little trace of segmentation left. The body of a typical mite can be divided into two regions, the gnathosoma or mouth and the idiosoma as the rest of the body (Fig. 1). The gnathosoma contains the Fig. 1 Ventral view of a mite (after von Vitzthum). Gn. = Gnathosoma, Id. = Idiosoma, Ta. = Tarsus, Ti. = Tibia, Ge. = Genu, Fe. = Femur, Tr. = Trochanter, Co. = Coxa, G.O. = Genital Opening.