Welsh Journals

MOSQUITOES IN NORTH WALES MRS. M. J. MORGAN The mosquitoes are two-winged flies, classified in the family Culicidae, characterised by their aquatic larvae and pupae which are both very active swimmers. The female lays her eggs either singly on the water surface or in batches which float like rafts. The larvae hatch out directly into the water and feed on minute particles of plant and other organic material. A pair of mouth brushes is continually moved through the water gathering food and transferring it to the mouth. At intervals the larva must rise to the surface of the water to take in oxygen through a long breathing tube, but swims rapidly away if alarmed. The pupa has a pair of breathing trumpets on the thorax and at rest hangs suspended from the surface film with the tips of the trumpets out of the water. When disturbed it swims down into the water but soon returns and it is here that the adult mosquito emerges. The skin on the upper side of the thorax splits and the fly pushes quickly upwards into the air and im- mediately takes to the wing. Sometimes numbers of cast skins can be seen floating at the edge of water tanks or pools from which mosquitoes have recently emerged. The male mosquito can usually be recognised with the naked eye by its antennae which are covered with long hairs and are described as plumose. The female has shorter and less hairy antennae but the most noticeable feature is the long needle-like proboscis, held out like a dagger in front of the head. With this she pierces the skin and sucks out a blood meal, at the same time injecting saliva. This is the chief cause of the irritation which persists often for some days after a mosquito bite. It is only the female which sucks blood, the males either not feeding at all or harmlessly frequenting flowers for nectar. In tropical countries a great deal of research work has been carried out into the life cycles and behaviour patterns of the various species of mosquitoes, especially those which are known to be responsible for trans- mitting malaria and other diseases. Detailed knowledge is essential before effective control measures can be carried out. Fortunately in Britain malaria is not the serious problem that it was in earlier centuries when fevers and ague, transmitted by Anopheles maculipennis, were very com- mon in lowlying and marshy areas. W. Rees Wright, writing in 1923, says "Ague was formerly endemic in parts of the North Caernarvonshire littoral. I have met several farmers who remember a time when it was often difficult to conduct agricultural operations owing to ague among the farm labourers. as far as I am aware there have been no locally contracted cases of malaria within the last few years." Perhaps the disappearance of malaria is the main reason why the study of the Culicidae has been rather neglacted in this country and there is a lack of up to date information about their present distribution. The presence of detergents can affect the ability of the larvae and pupae to breathe at the surface film. The widespread contamination of bodies of water by detergents may well have reduced the numbers of available breeding sites and consequently the mosquito population. Hence any in-