FARM PESTS 29 



on damp herbage and these hatch into a " nymph " or 

 preHminary form which is very similar to its parent, but 

 only has six legs, whereas the adult has eight. They 

 fasten themselves on to sheep or other animals and feast 

 upon their blood, dropping off when gorged and returning 

 again later for another orgy. They first appear in March, 

 and again in the autumn, and are commoner on the hill 

 pastures in the north than anywhere else. Here again 

 dipping will be of service, if repeated, to catch those 

 individuals who are " away on leave " as soon as they 

 come back. (See Plate 5.) 



We must now pass on to the Scab, Dermatodectes ovis, 

 which is another Acarus, and prevalent in places. Let 

 us just glance at its history. The sheep display much 

 restlessness under its attack and bite the affected parts 

 until they become sores, whereupon the Scab Mite moves 

 off to a fresh place, there to produce eggs and continue their 

 evil work. The Mite, when full-grown, is about 4'o inch 

 long and has eight legs covered with hairs, its larva having 

 only six, as shown in the sketch. It is not what one would 

 call an inviting-looking creature. Mites of similar appear- 

 ance but distinct in species produce mange in horses, 

 dogs and other animals, but the mange and the scab 

 mites confine themselves to their own particular host, so 

 that mange from dogs will not produce scab on sheep, 

 who must therefore get it from contact with their own 

 kind or by rubbing against fence-posts, etc., where the 

 mites and their larvae have been deposited. It is a notifi- 

 able disease and dipping must be done under the Sheep- 

 Scab order of 1905. 



All the above are external parasites of sheep, but there 

 are one or two internal parasites which claim attention. 

 There is, for instance, the Liverfluke {Distomum hepaticum), 

 whose history is a very curious one. Indeed it reveals 

 to us the extent to which all life is under the influence of 

 controlhng powers that are far beyond the wit of man to 

 fathom, working out a purpose we cannot guess at, because 



