146 
Psyche 
[June 
apacheanus. In the field, both opifex and apacheanus have been seen 
pursuing huge prey, such as grasshoppers and bees. A difference in 
preferred size of prey is also found between smaller and larger P. 
coccineus — although a 4 mm spiderling that pursued and caught a 
9 mm housefly provides a notable exception. Both these factors would 
reduce competition for food among the three Phidippus species. At 
the present time, preferred size of prey is being investigated with 
models (spheres 3, 6, 9 and 12 mm in diameter, moving at 8mm/sec.). 
Nest building 
As Phidippus spends the daylight hours wandering from branch to 
branch while hunting prey, it seems likely that a new nest is built 
every evening. In their laboratory containers, P. coccineus only occa- 
sionally built more than one nest; ordinarily, the spiders returned to 
the same nest, night after night. If however, the nests are removed 
in the morning, the spiders will build a new nest late that afternoon. 
On a typical test day, 19 spiders had their nests removed and were 
exposed to natural light conditions. Of these, 16 built a nest within 
the next 24 hrs. All nest building began in the afternoon, at a 
median time of 55 min. before sunset. (Such a generalization is 
limited to the sleeping nests of immature P. coccineus , for the molting 
nest is begun much earlier in the day, and the adult often lets many 
days pass without building.) 
The spider begins to build by moving within a limited area in the 
angle formed between the sides and top of the container. As it moves, 
it attaches a framework of threads of silk, each about two or three 
times its own length. Suspended within these lines, the spider starts 
to weave by moving the abdomen from side to side so that the 
spinnerets describe an arc of a circle. Moving forward and back a 
step at a time, sometimes suspended on its back and sometimes on its 
venter, the spider spins about itself a closely woven tunnel, roughly one 
and one-half times its own length. Once started, weaving continues 
uninterrupted, and by 30 min. after sunset most of the builders are 
quiet in their nests. The roles of light and temperature in the choice 
of nest-site and in the rather precise timing of this distinctive diurnal 
behavior are presently being investigated. 
Distribution of the species 
The male and female syntypes of P. coccineus came from Clare- 
mont, California and are kept in the Museum of Comparative 
Zoology. As far as known the species occurs in southern and eastern 
California and western Arizona. Phidippus opifex came from San 
