412 
Psyche 
[December 
gently with one of these movements, and immediately withdrew its 
leg and turned slowly 180° so that its abdomen was toward the prey. 
Carefully it drew out a strand of sticky silk with first one IV and 
then the other (as in Figs. 2 and 3) and then suddenly, with the only 
quick movement of the entire sequence, swung its hind legs upward 
to bring the sticky thread around the fly, and immediately began 
wrapping it with dry silk. 
Egg Sac 
Five different A. attenuatus were found with egg sacs. All sacs 
were elongate and white with a soft papery wall and small yellowish 
eggs loose inside the central portion. The spider rested either under 
the sac or adjacent to it with the legs extended in front and behind 
so that its outline merged with that of the sac. 
Discussion 
One of the unusual features of A. attenuatus is the presence of 
serrated bristles on the prolateral side of tarsus IV, and the absence 
of the comb on its inner surface that is usual for theridiids (Exline 
and Levi 1962). It is thus interesting that, at least in the single case in 
which leg and thread positions were observed in detail (right leg IV 
in Fig. 3), the sticky wrapping thread contacted the outer rather 
than the inner surface of the leg. This association is in accord with 
the general belief that serrated bristles and combs on the tarsi IV of 
theridiids serve to manipulate the wet wrapping silk which is 
apparently peculiar to this family. The advantage of holding the 
thread on the outer rather than the inner surface of the tarsus is not 
clear; perhaps it is related to the way in which the spider holds sticky 
thread poised just before wrapping (Fig. 2), a behavior unique to my 
knowledge in theridiids. 
The web structure, attack behavior, egg sac, and cryptic postures 
of A. attenuatus appear to be very similar to those of A. colubrinus 
(Clyne 1979). A. flagellum also apparently assumes the same cryptic 
posture. A. attenuatus differs from what is known of the other two 
in that it captures small flies and immature spiders as well as mature 
male spiders, apparently applies less wet silk as it wraps prey, and 
does not always rest facing up on webs. These spiders appear to be 
unique in having webs that serve as attractive resting sites and 
walkways for their prey. 
