20 
Psyche 
[March 
lays cribellar silk directly on the radii and frame threads of orb- 
like webs which lack a sticky spiral (Wiehle 1931). The spider ap- 
parently does not manipulate tensions in the web once it is built 
(Wiehle 1931: Figs. 14 and 17). Such a web might conceivably 
become reduced to a web like that of M. sp. 1 by loss of frame 
and auxiliary spiral threads and reduction of the hub to a single 
resting thread. On the other hand, the jagged pattern of the sticky 
spiral found in the egg sac webs of M. sp. 1 suggests an affinity 
with Uloborus (sens, lat.) or Hyptiotes (Uloboridae). Spiders of both 
these genera commonly lay a jagged, sticky spiral on the periphery 
of the orb (McCook 1889, Eberhard 1972, Eberhard, unpubl.). An 
unidentified species of Uloborus (sensu strictu) builds an essentially 
identical egg sac web (Eberhard, in prep.), and Uloborus diversus 
also places sticky silk around its egg sacs (Eberhard 1969). 
The most likely adaptive advantage of a single thread capture 
web would seem to be its near invisibility to prey, since at least 
some flying insects can detect and avoid webs (Bristowe 1941, Rob- 
inson and Robinson 1970, 1973, Lubin 1973, Buskirk 1975, Eber- 
hard in prep., Lahman and Zuniga in prep.). This is apparently 
ruled out, however by the fact that at least two species (Af.sp.3 and 
the New Guinea species) and perhaps a third ( M . intempus) usually 
build their webs at night when visibility is probably unimportant. 
Another possible advantage would be that predators using webs 
as cues to the presence of prey would be unlikely to detect webs of 
Miagrammopes. Some predators may use webs in this way, though 
some are known not to (Eberhard 1970). The significance of the 
very thin, slack lines attached to the capture threads remains even 
more of a mystery. 
The obvious disadvantage of a single thread capture web is the 
low probability of a flying insect striking the web. Robinson and 
Robinson (1976) suggested that the numerous nematocerous flies 
which tend to rest on non-sticky spider threads might try to alight 
on Miagrammopes capture threads and thus become entangled. 
Indeed Akerman (1932) noted a number of “gnats” caught by the 
Miagrammopes species in Natal. Some nematocerous flies were 
among the prey collected in this study, but many other kinds of 
small insects were collected as well. Certainly the webs of Mia- 
grammopes are not specialized to the extent of exclusively or even 
principally capturing nematocerous flies which alight on them. Some 
other spiders with reduced webs use chemical attractants for spe- 
