1976] 
Jackson — Phidippus johnsoni 
249 
recognized the gnaphosid visually, since salticids are known to 
have highly developed visual abilities (Land, 1972). 
Incidentally, after these observations, the gnaphosids were 
kept for one week in the cages with the P. johnsoni nests and 
eggs. However, the eggs remained undamaged, lending no sup- 
port to the hypothesis that gnaphosids prey on P. johnsoni eggs. 
Nest Discrimination 
Each P. johnsoni male used in these observations was exposed 
to an empty nest of a P. johnsoni female and an empty H. hes- 
perolus nest on successive days. Half were exposed to P. john- 
soni nests first, the other half were exposed to //. hesperolus 
nests first, and the spiders were assigned to the two groups ran- 
domly. On the day before the observations, nest occupants were 
removed. No nests contained eggs. The nests of H. hesperolus 
were similar in shape and size to the nests of P. johnsoni; but 
they differed substantially in silk texture; and they were more 
transparent. Each nest was used in only one test. The P. john- 
soni male was introduced into the cage through a hole, and ob- 
servation continued for 15 min after the spider touched the nest. 
During both type 1 and type 2 courtship, as well as during 
conspecific aggressive interactions, the abdomens of P. john- 
soni males twitch in a characteristic manner (Jackson, 1976), 
that is not seen in other contexts. The abdomen of each male 
twitched while he was on the empty nest of a P. johnsoni female, 
but not while he was at the nest of a H. hesperolus (McNemar, 
X 2 = 4.1667, P < 0.05). In addition, each male performed two 
elements of type 2 courtship, probing and tugging, while at the 
empty P. johnsoni nest. Two males vibrated at the P. johnsoni 
nests, and none vibrated at the H. hesperolus nests; however, 
these frequencies were not significantly different. Males of other 
species of spiders are reported to show elements of courtship 
behavior when they touch the silk of conspecific females (Don- 
dale and Hegdekar, 1973; Hollander, et a /., 1973; Kaston, 1936). 
The P. johnsoni males remained on P. johnsoni nests for longer 
time periods than on H. hesperolus nests (Table 1) (Wilcoxon, 
one tailed test P < 0.05). Courtship at the empty P. johnsoni 
nests lasted 1 to 7 min. Three males entered the P. johnsoni 
nests. Two of these also entered the H. hesperolus nests, these 
