PREDATION AS A SELECTION FACTOR IN THE 
MATING STRATEGY OF THE JUMPING SPIDER 
PHIDIPPUS JOHNSONI 
(SALTICIDAE, ARANEAE) 
By R. R. Jackson* 
Department of Zoology, University of California 
Berkeley, California 94720 
Introduction 
Predation risks are often considered to be a major selection 
pressure related to the courtship and mating behavior of ani- 
mals (Emlen, 1973; Morris, 1956; Richards, 1927; Strong, 1973). 
The importance of this factor in the mating strategy of a salti- 
cid spider, Phidippus johnsoni (Peckham and Peckham), will 
be considered here. In this species, each individual male has 
at his disposal three alternative mating tactics (Jackson, 1977). 
The one used depends on the female’s maturity and whether 
she is inside or outside her nest. Nests are silk structures that 
the spider constructs under rocks and in other rather dimly lighted 
locations. These are occupied during inclement weather, at night, 
during molting and oviposition, and at other times. When the 
male encounters an adult female outside her nest, he performs 
a form of visual courtship (type 1), consisting of various pos- 
tures and movements performed in front of the facing female. 
A form of non-visual courtship (type 2) is employed when the 
female is encountered inside her nest, consisting of various forms 
of shaking and plucking on the silk of the nest. If the female 
is a subadult, the male may construct a second chamber on her 
nest and cohabit until she matures. Observations will be pre- 
sented, implicating certain spiders of the family Gnaphosidae 
as predators of P. johnsoni. These incidences of predation occur 
while the salticids are at their nests and during courtship. 
P. johnsoni is a common, euryecious salticid species in western 
North America. Often other organisms are found associated 
with nests of this species, both ones that are occupied by P. john- 
* Present address: North Carolina Department of Mental Health Research, Box 
7532, Raleigh, North Carolina 27611 
Manuscript received by the editor February 10, 1977 
243 
