British Hydracarina. 



Abstract of lecture by Chas. D. Soar, F.L.S., F.R.M.S., 

 Given October IQth, 1921. 



Students of insects, known as Entomologists, find the pursuit of 

 tiaeir own study so very absorbing and interesting, that we find very 

 few who will turn aside to give some portion of their time to the 

 Acarina or mites. Why this should be, I am unable to say, one 

 appears to me to be as interesting as the other, and of quite as much 

 importance, particularly from the economic point of view. As a 

 proof of this, of all the mites, the Ticks, I suppose, have caused 

 more trouble than any other super-family of the Acarina, and in 

 consequence they have received more attention than the other 

 groups, particularly in America where some very fine work has been 

 done. But I have not come before you to talk about Ticks, I only 

 mention them as an example of how interesting the study of the 

 Acarina has proved in the country in which they have caused such 

 trouble to the live stock. 



The Acarina or mites form an order in the great Class Arach- 

 nida. They are closely related to the Spiders and Scorpions. 

 Several attempts have been made at classification : the best, I think 

 is by Banks, who divides the order into eight super-families of which 

 Hydrachnoidea is one. The super-family is again divided into two 

 families, the Halacaridae (Marine Mites), and Hijdracarina, nearly 

 the whole of which are found in fresh-water. It is with these fresh- 

 water mites that we are concerned this evening. 



The Hydracarina have been known for some considerable time, 

 but no serious work or description was attempted until 0. F. Miiller 

 described the Danish species in 1781. Miiller, in his work on the 

 water mites, figures and describes forty-nine species in all. It is a 

 very beautiful little volume with all the figures coloured. Since 

 Muller's time so much work has been done that we now have 

 considerably more genera than Miiller described species, and of 

 species themselves over a thousand have been described and recorded 

 from different parts of the world. For the area of Britain aloue we 

 have recorded about 250 species representing about forty genera. 



The full-grown adults vary very much in size, from half a mm. 

 to eight mm. long according to species. The females are always 

 larger than the males, particularly so if the females are in a gravid 

 state. But even then the difference is not so great as we find in the 

 ticks. 



The bodies are more or less oval or round, with some exceptions 

 amongst the males of one or two genera. Sometimes laterally the 



