THE ACAEINA OR MITES. 



47 



c^?^ 



deutovum. The larva (figs. 80, 81 j on hatching is six-legged, and in some cases is 

 parasitic in the respiratory system of mollusks or attached to aquatic insects. Neu- 

 mann has claimed that in one species of Limnesia the form hatching from the egg is 

 eight-legged and therefore a nymph, as in Spintumix. Kramer has arranged the 

 larvae in three series, which he 

 considers is the basis of classifica- 

 tion. As a whole, the larvae differ 

 greatl}^ from the adults and many 

 were described as different crea- 

 tures. Some were the basis of the 

 genus Achlysia. 



The larva usually has very 

 small mouth parts. It fastens to 

 an insect by means of hooks at 

 the tip of the short, stout palpi, 

 inserts its jaws, and proceeds to 

 feed. Gradually the body be- Figt 76.— Genital suckers of Hydrachnids: a, Bydrochor- 

 comes swollen, the legs shrink, ^utes, Fiona; b, Hydrobates, Mideopsis, Lebcrtia; c, Lim- 

 and the creature looks like an nesia; d, Atax; e, Arrenurtis.' f, Nesaea. (Original.) 

 elliptical egg. The pupa is formed 



within this saclike body, and from it in time issues the adult mite. Frequently 

 mature insects such as mosquitoes, whose early stages are passed in the water, 

 have many immature hydrachnid mites clinging to them. These mites have 

 made a serious mistake, and out of the water must soon die. It is probable 



that they were attached to the 

 insect pupa, and at its trans- 

 foimation moved to the adult 

 without suspecting the suicidal 

 result . These mites in the water 

 must often have to change when 

 their host larva molts, so that 

 they realize when a change l*^ 

 imminent, and relax from tn^ 

 old skin at the right time to 

 attach to the emerging insect. 

 It has been noted by Miiller 

 that when Lihellula was heavily 

 infested with the immature 

 stages of certain red water mites 

 there were about as many speci- 

 mens on the wings of one side 

 as those of the other side, so 

 that the insect had a prettily 

 and evenly maculated appear- 

 ance. On most insects, however, there is no plan of attachment, but specimens often 

 occur at the ventral base of the abdomen. 



Nearly all Hydrachnidae live in fresh water, a few forms occur in brackish water, 

 and several are known from the littoral zone of the sea. They are sometimes parasitic, 

 as already noticed, and feed on any small animals they can catch, such as small Crus- 

 tacea, infusoria, and minute insect larvae. The water mites are found throughout the 

 globe, but appear to be most numerous in temperate regions. Many species inhabit 

 rapid stream.^ and very cold water. Some species are rather sociable and occur in 

 colonies among small patches of water weeds. A great many species have been described 

 from tropical countries, most of which belong to European genera . Over 60 genera and 



88854°— 15 4 



Fig. 



-ArrenuTus sp.: Male. (Author's illustration.) 



