Figure 5.9. The Fire-bellied Snake (Liophis epinephalus), a diurnal frog-eater that has declined
throughout the Monteverde area. It is eating a Harlequin Frog (Atelopus varius). Photograph by
Michael and Patricia Fogden.Snakes and Peppered Tree Snakes (Duellman and
Trueb 1986, Donnelly 1994), and the terrestrial eggs
of rain frogs are food for Glossy Litter Snakes, Pink-
bellied Litter Snakes, and Faded Dwarf Snakes (Hayes
1985, Seib 1985). The aquatic eggs and hatchling tad-
poles of Meadow Treefrogs are vulnerable to canni-
balism by larger tadpoles (Crump 1983,1990,1991b),
and all developmental stages are susceptible to pre-
dation and drying of pools. Predators of the tadpoles
include Fire-bellied Snakes, aquatic insects, and (in
Zone 6) tadpoles of the Smoky Jungle Frog, which
also eat the eggs (Heyer et al. 1975). In experiments
with predaceous diving beetles (Dytiscidae) and drag-
onfly nymphs (Aeshnidae and Libellulidae), the most
vulnerable tadpoles were very small ones and those
passing through the four-legged stage (Crump 1984).
All stages were equally vulnerable to nymphs of some
dragonfly species. In experimental simulations of
drying pools, tadpoles developed at enhanced rates
and transformed at reduced body sizes (Crump
1989a).
Predators of adult amphibians range from ctenid
spiders (Hayes 1983) to snakes, birds, and mammals.
Freshwater crabs, which sometimes prey on small
anurans (Duellman and Trueb 1986), are common
along streams. Larval tiger beetles (Cicendelidae)
position their traplike jaws at the entrance to their
burrows; twice I have seen a Harlequin Frog with a
foot ensnared. Frogs might lose digits or limbs to
these predators. Snakes are among the most impor-
tant predators of frogs and toads. Many colubrids
feed primarily or exclusively on anurans, and some
eat highly toxic species with apparent impunity. Fire-
bellied Snakes, for example, prey on Harlequin Frogs,
despite the presence of a potent nerve poison (tetro-
dotoxin) in the skin of these anurans (Kim et al. 1975;
Fig. 5.9). Among the many birds that capture frogs are
Sunbitterns and Blue-crowned Motmots. Resplendent
Quetzals sometimes feed frogs to nestlings (Wheel-
wright 1983).
Parasites of adult amphibians include fungi, hel-
minths, leeches, arthropods, protozoans, bacteria, and
viruses (Hoff et al. 1984, Duellman and Trueb 1986).
The impacts of these organisms on populations are
largely unknown. A female sarcophagid fly (Noto-
chaeta bufonivora) deposits larvae on the back of a
Harlequin Frog's thigh. After making a small opening
in the skin, the larvae feed on muscle tissue before
entering the body cavity and causing death within
a few days (Crump and Pounds 1985, Pounds and
Crump 1987). During the dry season of 1982-83, the
probability of being attacked by these flies was great-
est in waterfall spray zones, where the frogs were most
abundant. Experiments in which frog density was160 Amphibians and Reptiles