PSYCHE 
Vol. 84 March, 1977 No. 1 
ATTACKS ON LARGE OR HEAVILY DEFENDED PREY 
BY TROPICAL SALTICID SPIDERS 
By Michael H. Robinson 1 and Carlos E. Valerio 2 
Introduction 
Spiderlings in the first active instar have severe limitations in 
prey capture, because of their small size (Valerio, 1975) and par- 
ticularly in those species that ambush or stalk their prey. The pres- 
ence of snares or catching webs characteristic of several families 
expands considerably the range of potential prey items, which is 
undoubtedly an important pressure in the evolution of such struc- 
tures. Even web-building spiders have problems with the large 
heavily-sclerotised prey items (see for instance Robinson & Robin- 
son 1973a, 57-58). Insects with chemical defenses also prove trouble- 
some to spiders (Eisner & Dean, 1976). However, the use of silk in 
the immobilization wrapping of araneid spiders considerably en- 
hances their ability to subdue large or heavily defended prey (see 
experimental analyses summarized in Robinson 1975). 
Salticids, on the other hand, are among the hunting spiders that 
subdue their prey without the aid of silk. For this reason, it is 
widely assumed that they are limited, in general, to prey which is 
smaller than themselves or to soft-bodied defenseless items (Enders 
1975, 745 and references). At first sight this assumption seems 
perfectly reasonable, since the salticid attacking prey larger than 
itself must contend with a strength (perhaps) superior to its own. 
The insect under attack would presumably push against the sub- 
strate and exert sufficient pressure either to escape or to injure 
■Smithsonian Tropical Research Institute, P.O. Box 2072, Balboa, Panama 
Canal Zone. 
2 Escuela de Biologia, Universidad de Costa Rica, Cuidad Universitaria, Costa 
Rica. 
Manuscript received by the editor June 8, 1977. 
