236 Acarology 



Genus: 



Demodex Owen, 1843 



Type. Acanis foUiculorum Simon, 1842 



Discussion: Demodex muscardini Hirst, a parasite of the dormouse, 

 Muscardinus avellanarius, illustrates a complete life cycle of these 

 mites. The eggs hatch into a larva which is very much like the early 

 nymphal stage, except that there are three instead of four pairs of legs 

 which consist of a chitinous plate or epimeron; each epimeron bears 

 a pair of very minute and inconspicuous denticulate tubercles. The 

 protonymph has four pairs of legs or epimera, each bearing two tiny 

 but distinct tubercles of equal size, each with three or four minute but 

 distinct denticles. There are four pairs of curious epidermal structures 

 present nearer the middle of the ventral surface of the body. These are 

 semicircular in shape, and the posterior margin is curved and furnished 

 with sharp denticles. The deutonymph has the appendages or legs simi- 

 lar to those of the protonymph, but they are more leglike with several 

 segments visible and with two clusters of denticles present. The four 

 pairs of semicircular structures in the ventral surface are present but 

 are much smaller. The adult has the genital opening, five-segmented 

 legs, and has lost the semicircular structures on the ventral surface of 

 the body. 



Hirst 1919 gives an excellent review of the family from which the 

 following information is taken. Demodex foUiculorum Owen, which is 

 to be found in the pores of man, especially around the nose and eye- 

 lids, has been implicated in various skin diseases. It has been noted, 

 however, that these mites occur in normal as well as diseased tissue 

 and are to be found infesting most people. It is now believed to be of 

 no importance in man. Like the following species it is more or less 

 world-wide in distribution. D. cams Leydig is present in the follicular, 

 demodectic, or red mange of dog. In typical cases the mite is to be 

 found in great numbers in association with a bacterium {Staphylococcus 

 pyogenes albus or some allied form), which is the actual cause of the 

 disease. The mite plays an important role in that it dilates the follicles 

 and sweat glands and even possibly carries the germ into the pores. 

 The mange may be pustular, accompanied by various crusts; it may 

 be a "squamous affection with numerous epidermal pellicles. In a 

 typical case there are small hairless patches, together with reddish 

 pimples and pustules, skin hot and thickened in the affected places." 

 There is a foul and disgusting odor accompanying this mange. The 



