ENEMIES OF APHIDES. 373 



and appears capable of being opposed to the latter. In Holoscri- 

 ceum this process is so clothed with stiff bristles as to assume 

 somewhat of a hard character, while in other species a rounded, 

 fleshy structure obtains. 



Some varieties are known to be vegetable feeders, and are 

 believed to do considerable damage to plants and trees, to the 

 under surface of the leaves of which they usually attach them- 

 selves and suck the sap much as do the aphides. But Tetranychus 

 telarius, Trovibidiion Holosericeum, and other species prefer either 

 a mixed or a wholly animal diet, and as the vegetation which they 

 frequent is also the habitat of some of the most prolific species of 

 aphides, the juicy insects afford a convenient and, we may pre- 

 sume, a palatable nutriment. For with the opportunity the meal 

 is repeated, and in the presence of plenty the Aphis-eating habit 

 has become established. 



These Arachnida during their early stages are frequently para- 

 sitic on some more bulky host either of the insecta or of their own 

 class. Thus, T. Holosericeum frequently passes its larval period on 

 the body of the slender Harvest Spider, where it attaches itself to 

 the under surface of the abdomen, or thorax, and may be ob- 

 served as a scarlet spot, which becomes more prominent as the 

 mite grows in size, and where it at length quits its protecting, 

 though possibly not unwilling, host. It finds in the soil a retreat, 

 where a period of rest analogous to the pupal stage of insects is 

 passed. Two or three weeks suffice for the change, and the 

 minute ovoid nymph produces an eight-limbed mite, which be 

 comes in turn the parent of a new generation. 



I have observed the young of a very minute species which I 

 have been unable satisfactorily to identify thus parasitic upon the 

 large black aphis of the poppy, and I cannot avoid the conclusion 

 that, in this case (and probably in the former one), the larva draws 

 its nutriment from the host to which it is attached. It is stated 

 that some species undergo their transformation without quitting 

 their host, but I have myself not been able to confirm this. 



The identification of the different species of these curious 

 creatures presents some difficulties, but I have been able to satisfy 

 myself that Tetranychus te/arius, Linn., Trombidhini Holosericeum, 

 Tetranychus tiliarum, Miiller, and a robust specimen covered with 



