Figure 4.18. Scorpion. Photograph by Barbara Clauson.Spiders are divided into two major groups: the
wandering spiders (e.g., jumping spiders, wolf spi-
ders, and crab spiders) and the sedentary web spiders.
All spiders have spinnerets on their abdomen and use
silk for making egg sacs, but only web spiders use silk
in the building of complex snares to capture prey.
Among web-builders, different families build differ-
ent types of webs (Eberhard 1990). For example,
Agelenidae weave a horizontal, slightly concave silk
mat with a funnel-shaped retreat at one end; Liny-
phiidae construct horizontal, slightly convex sheets;
Theridiidae and Pholcidae build irregular meshes.
The best-known webs are orb webs, which consist of
radial threads converging on a central hub, outer
frame threads that serve as insertion sites for the ra-
dial threads, and a sticky spiral.
Our knowledge of cloud forest arachnids is ex-
tremely rudimentary. Four families and 14 species of
scorpions are known from Costa Rica, the most com-
mon in Monteverde being Centuroides limbatus
(Buthidae), which occurs in different color morphs
(Francke and Stockwell 1987; Fig. 4.18).
4.8.2. Vertical Distribution of Orb-Weaving
Spiders in a Colombian Cloud Forest
Carlos Valderrama A. (translated by Bob Law)
I measured the vertical distribution of spiders in a
Colombian cloud forest (Reserva Natural La Planada,
1850 m), a site that is similar in elevation and vegeta-
tion to Monteverde. Spider communities were com-
pared among three habitats: closed-canopy primary
forest (selectively cut in 1981, 15 years before this
study), secondary forest (regenerating cattle pastures
that had been abandoned more than 10 years before),
and natural clearings (formed by recent tree falls
within the primary forest; Valderrama 1996). The
vertical distribution of flying insects (putative prey)
was compared in the three habitats with sticky traps.
A total of 1188 adult spiders were collected, repre-
senting 46 species and eight families (Anapidae,
Araneidae, Deinopidae, Mysmenidae, Symphytog-
nathidae, Tetragnathidae, Theridiosomatidae, and
Uloboridae).
Very few spiders were captured in the canopy,
most of which were juveniles and small adults. The
juveniles belonged to understory species, which may
reflect their high capacity for aerial dispersal. In
canopy fogging studies, only 2% of the arthropods
collected in the canopies were spiders (Erwin 1989).
This suggests that spiders may not be more diverse
in the canopy than the understory, as are many other
arthropod species.
The greater availability of support structures, for
example, epiphytes on trunks in the primary forest,
apparently allows many species to expand their ver-
tical range. Epiphytes also provide refuges for spiders.
For example, Azilia normally builds its horizontal140 Insects and Spiders