xo. 7 



PROTECTIVE x\DAPTATIONS McATEE lOI 



Discussion. — All spiders have venom and some of them are large 

 and venomous enough to be able to kill birds. The case would seem 

 to be crucial for the usefulness of this direct means of defense, but 

 we may well say, in the light of the evidence, that the defense is 

 entirely disregarded by birds. Xot only do our records show more 

 than 10,000 records of spiders having Ijeen eaten by more than 300 

 species of birds, but the birds emphasize their disregard for the 

 dangerous qualities of spiders by making them in many cases the 

 staple food for their callow young. Such minor protective adaptations 

 as those of color and form necessarily fall with the greater, and there 

 is no evidence whatever but that birds eat spiders under any and all 

 conditions as freely as they choose. The nearly 1,000 records of 

 arachnids other than spiders seem to be distributed among the orders 

 in verv just proportion to the extent these creatures are available to 

 birds. No evidence of " special protectedness " obtrudes itself. 



MOLLUSCA (SNAir,S, SLUGS, MUSSELS, LIMPETS) 



Protective adaptations. — The great majority of mollusks arc 

 equipped with calcareous shells into which they can entirely withdraw. 

 Besides this protection more than half of the species are aquatic and 

 hence are more or less out of reach of many birds. Many land snails 

 have the apertures of their shells furnished with processes or teeth 

 which partly bar these openings and operculi to close them. Snails 

 and especially slugs secrete mucus freely ; a habit thought by some to 

 be protective. Numerous mollusks are colored more or less in harmony 

 with their environments, this being especially noted of marine forms 

 living on seaweeds, gorgonians, etc. The nudil)ranch mollusks are 

 characteristically brightly colored and ha\-e been said to 1)e distasteful. 

 Of shelled mollusks, Wallace remarks : " The brilliant colors of the 

 scallops (Pccten) and some other bivalve shells are perhaps an indica- 

 tion of their hardness and consequent inedil:)ility." ( Darwinism, 

 p. 266-267, 1896.) 



Bird enemies. — The tabulation of identifications herewith presented 

 is the I)est that could be made so far as comparative records is con- 

 cerned ; these had to be gleaned from two sources as noted, which 

 between them do not include all of the families, nor. because of 

 disparity of data, do they give even the grand divisions comparable 

 treatment. 



