222 AMERICAN SPIDERS 



species. This spider does not walk in a straight line, but, with abdo- 

 men twitching at intervals, "zigzags continually from side to side, 

 exactly like an ant which is out in search of booty." The thicker 

 front legs are used for walking and support of the forward part of 

 the body, but the second pair is raised above the others and made 

 to resemble the antennae of ants. The substitution of the second 

 legs for the role played normally by the first pair suggests that the 

 antlike gait and stance may have been acquired after the front legs 

 had already been committed beyond redemption to another use. 

 Even while feeding, Peckhamia picata "acts like an ant which is 

 engaged in pulling some treasure-trove into pieces convenient for 

 carrying," and keeps beating the prey "with her front legs, pulling 

 it about in different directions, and all the time twitching her ant- 

 like abdomen." The related species, Peckhamia americana, was ob- 

 served by Prof. W. M. Wheeler running up and down the trees 

 in Florida in files with the ant Camponotus planatus. 



The Peckhams attributed the low fecundity of Peckhamia picata 

 (said to produce only three eggs) to its resemblance to ants. As 

 have most exponents of ant mimicry, they assumed that ants have 

 few enemies and reasoned that protected mimics would not have to 

 produce so many offspring to maintain their normal population. It 

 seems to be true that many predators shun ants or find them dis- 

 tasteful, and that antlike spiders profit from this aversion. How- 

 ever, insufficient data on ant mimic fecundity are available to war- 

 rant the conclusion that the real protection mimics enjoy results in 

 lowered egg production. Instead, low production seems to be re- 

 lated to body size and minimum egg size, which limit the number of 

 eggs that can be matured for a single laying. Likewise, immunity 

 to the attack of the Pompilid wasps often cited as evidence for ant 

 mimicry is largely a consequence of size inasmuch as most antlike 

 spiders are too small to serve as larval food for the wasps. 



The ant mimicry of the jumping spiders is distinct from that of 

 other spiders in that they never enter and live in the nests of ants. 

 The dark of ants' nests would take from them full use of the sense 

 that has brought them greatest success among the vagrants. 



THE CRAB SPIDERS 



The superficial resemblance of some two-clawed vagrants to 

 crabs has given them the name of "crab spiders," and their ability 

 to move sidewise or backward with great facility enhances the per- 



