OF WASHINGTON. 6 



where the cryptic resemblance is intended to deceive possible 

 prey, and perhaps incidentally to escape enemies ; this is 

 termed " anticryptic resemblance " by Poulton ; the other class 

 includes those cases where the cryptic resemblance is intended 

 to deceive possible enemies, the " procryptic resemblance " of 

 Poulton. The species belonging to the first class are often 

 common, even abundant ; and the success of their devices is 

 shown by their abundance. To this class belong many spiders 

 of the family Thomisidae (Misumena, Runcinia, etc.). The 

 species of the second class are rarely common in specimens. 

 The success of their devices must be judged by the percentage 

 that escape their enemies. Many authors reason that if a 

 protected species is captured, the protective device is a fail- 

 ure. It is just the opposite. The success of their enemies 

 was the cause of protective resemblance, and at least occasional 

 captures must continue, not only to maintain the protective 

 device at its present state, but to increase its efifectiveness. 

 And side by side with the development of the protective device 

 in the prey, goes, in many cases, the increased power of de- 

 tection in the enemy. Of course some species, by just the 

 right method, may secure practical exemption from capture ; 

 and their former enemies must seek other food. But with the 

 large majority of cases the protection is not perfect. It is 

 simply a help in their struggle for existence, not always the 

 main reliance, which may be in great fertility, or facility in 

 obtaining food. 



The chief enemies of spiders are insects, mostly certain 

 Hymenoptera. Some authors take it for granted that birds 

 are the great enemies of both insects and spiders. Such is 

 not the case. Insects, as well as spiders, suffer mostly from 

 the ravages of other insects. So to argue that since birds eat 

 certain supposedly protected insects, the protection is of no 

 value, is quite misleading ; for the coloration may be effective 

 against certain insect enemies. There are, as all know, cer- 

 tain families of insects which in their adult stage have more 

 to fear from birds than from insects ; but it is not the rule. 



The principal insect enemies of spiders fall in three groups : 

 Parasites, Pompilidse, and mud-dauber wasps. I do not 



