CHAPTER 12 



MITES (AGARINA) 



They are so small that Epicurus said it was not made of 

 Atoms but was an Atom itself . . . 



Thomas Mouffet 



THE MAJORITY of mitcs havc roughly globular bodies, with their head 

 and thorax fused, two pairs of mouth-parts and four pairs of legs in 

 the adult stage. The larvae have only six legs when they hatch, but after 

 a certain number of moults develop into nymphs with the full comple- 

 ment of legs. They are so small that it is necessary to have recourse to 

 the microscope in order to see their structure. The number of species of 

 free-living mites only outnumbers the parasitic mites by about three to 

 one, and it is believed that parasitism must have arisen independently 

 about a dozen times in the group. If ever an assembly of animals were 

 pre-adapted to this particular mode of life it is the mites, not only on 

 account of their minute size and varied feeding habits, but also because 

 of their insatiable desire to wander about and creep into cracks and 

 crevices. Except in a few families they are not greatly changed by their 

 dependent existences. Mites living as ecto-parasites, however, even in 

 distantly related suborders, develop striated cuticles. This is another 

 case of parallel evolution which, like the development of combs on 

 insects, appears to be the direct result of life in fur and feathers. 



The best known group parasitising birds is that of the red mites 

 (Dermanyssidae) which hide and breed in nests and under the bark of 

 trees and creep out at night to suck the blood of the host. A common 

 species in Britain is the swallow red mite [Dermanyssus hirundinis) which 

 greatly resembles the common red mite of poultry {Dermanyssus gal liriae), 

 also widely distributed in the nests of many wild birds, including various 

 passerines, gulls, and pigeons. D. quintus is a parasite confined to the 

 green woodpecker, and D.passerinus from the greenfinch is an interesting 



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