100 ON SOME COMMON Sl>ECIES 



says, evidently cjuoting Duges, in reference to the family Gaina- 

 sidic : — " It is a ]3eculiarity of all the parasites on insects, that 

 they soon die after being removed from the insect or from the 

 stone under which they have taken refuge, unless they are kept 

 moist." 



From my own experiments, I have found that it is the want of 

 moisture alone which causes their speedy death, and that they 

 will live for days on water only. One day in December, I picked 

 up a Geotrupes half dead, that had upon it several Gamasids of 

 different species, and laid it on its back in a small box. After 

 three days, most of the smaller Gamasids were dead (the beetle 

 being still alive), but the larger ones — those with the divided 

 dorsal plate {ColeoptnUorum) — were, to all appearance, quite well ; 

 but they had quitted their usual position between the fore-legs, 

 and were congregated round the mouth, their mandibles and lesser 

 ])alpi being quite hidden within it. This, I have no doubt, they 

 did as being the only place where they could still find moisture. 

 I then killed the beetle, and placed its head only, with the 

 (xamasids still attached to it, in the box, and the next morning 

 they were all dead. 



On one or two occasions, I have allowed the cells to become 

 rather dry, and in consequence several of the smaller mites have 

 died ; but Cokoptratumvi seems less intolerant of dryness, and 

 the only one of this species which I lost during the first two 

 months I kept them confined was accidentally crushed. I make 

 little doubt that the closely-allied species found on Humble Bees 

 will prove to stand want of moisture still better. 



I had not kept my Gamasids many days on vegetarian diet 

 when I fortunately came across a ])aper by Mr. A. D. Michael, 

 the author of a monograph on the British Oribatidic^ in which he 

 mentioned having fed Gamasids on cheese-mites, and I tried the 

 experiment with i^erfect success. I have several times seen the 

 smaller species in the act of eating the cheese-mites. They 

 suddenly darted out their mandibles and pierced the mite's body ; 

 the mandibles were then alternately withdrawn and protruded, 

 turning from side to side within the body of the cheese-mite, like 

 two spoons .scooping out an egg ; and in a few minutes there was 

 little left but an empty skin. I believe they use the chelate ends 



