6 



Their first duty appears to be to look out for a suitable host on 

 which to feed and develop towards the next stage. We used to 

 think that each species had its own favourite host, but now we 

 find that some are not so particular, as some species of larvfe are 

 found on different insects. HydraracJma globosa is a good example 

 of this. It has been found on Nepa, Dtjtiscus, Ranatra and others. 



Lmnochares aquatica larvae are parasitic on Gerris lacustris. 

 Species of Eylah on Dijtiscns ; they are also reported as being found 

 on Dragonflies and on Tipulidae. A species of Hydryphantes I found 

 on a fly, Caenia nbscnra, Mg., the larvffi of which live in water-plants. 

 Species of Hydrarachna are found, as already mentioned, on 

 Dytisridae, Banatra, Hydrophilii.t and Nepa. Hyr/mbates lonyipalpis 

 I have found in fresh-water sponge in the larval stage. Several 

 species of Unionicola are found in Unto and Anodonta. One species, 

 Unionicola crassipes, I have found several times in all stages in 

 fresh-water sponge. Species of the genus Arrhenurux the largest 

 genus we have, have been found on Dragon-flies. Krendowsky 

 gives a figure of a Dragon-fly with the wings showing a number of 

 parasitic larvte, which he says is Arrliennrus papillator, Miill. I 

 have taken a number of Odonata with the larval parasites, but I 

 have never been able to identify the species. I cannot do better 

 than refer those interested to a paper by Dr. C. Wessenberg-Lund 

 " Contribution to the knowledge of the postembryonal development 

 of the Hydracarina," 1919. 



At the end of the larval stage — which if all are parasitic must 

 vary very considerably in the time spent on the host — in those we 

 know of, the posterior end of the envelope breaks away and the 

 nymph escapes and becomes at once a free swimming animal 

 like the adults, with eight legs in place of the six in the previous 

 stage. They are no longer parasitic, but forage for themselves. 

 They are very like the adults in general appearance except in the 

 provisional genital area. Of course, they are much smaller and in 

 the majority of species the sexes cannot be identified in this stage. 

 After some time as nymphs, a period that no doubt varies with the 

 species, they pass into the adult stage, and in the higher forma 

 attain that variety of beautiful colouring for which they are noted 

 and also the great differences in structure so noticeable amongst the 

 Arrhenuri. 



Such in brief is an outline of the little known life-history of 

 these interesting creatures. 



Slides showing the larvae, parasitic stages, and species of the 

 principal genera were thrown on the screen ; several being in colour 

 taken direct by Mr. Taverner from the living mites. 



