THE DIPTERA. 407 
The Bee Louse or Tick may be compared to a spider fly, and 
is about two-thirds of a line long. It is pupiparous, like the 
sheep tick, and the very day it is hatched it sheds its skin and 
changes to an oval pupa of a dark brown colour. Packard states 
that its habits resemble those of the flea, and that it is evidently a 
connecting link between the flea and the two-winged flies. Like 
the former, it lives and brings forth its young on the body of its 
victim or host, and draws its food by plunging its stout beak into 
the skin of the bee ; and sometimes one of these industrious insects 
may be seen to be weighed down by as many as a hundred of 
these bloodthirsty creatures. 
The varieties of metamorphosis in the Dzpiera are thus very 
considerable, and it must strike every observer that the most 
decided transformations are those of the parasitic flies. This is 
one of the proofs that the metamorphosis has been gradually 
added to the evolution of the insect, and that it is preservative of 
the species. 
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