Pachycondyla aenescens, and Odontomachus opaci-
ventris. Leptogenys imperatrix is a specialized preda-
tor on isopods. Workers scurry across roads or trails,
often carrying isopods in their jaws. Their colonies
are small, and nests are common and easily spotted
in the soil along road cuts in the Monteverde commu-
nity due to the tell-tale light gray streak of ejected
isopod shells below the nest entrance. Foraging work-
ers of Pachycondyla aenescens are commonly seen on
roads in Monteverde and take a wide range of prey.
Pachycondyla aenescens is a montane species, occur-
ring above 1000 m in the northern Neotropics (W. L.
Brown, pers. comm.). Odontomachus is a genus of
large ants with long snapping jaws (Brown 1976).
Odontomachus opaciventris, a primarily montane
species, is the most common species in the Monte-
verde area. Nests are in rotten wood and may be com-
mon around dwellings. Winged queens are a common
sight. They are generalist predators that actively hunt
for prey and have a powerful and rapid sting.
Cloud forest leaf litter ants. Leaf litter in the cold wet
cloud forest appears to support no ants, but actually
harbors a moderately diverse community (Longino
and Nadkarni 1990, Nadkarni and Longino 1990).
Cloud forest litter ants are "cryptobiotic": they forage
in and under the litter, feign death when disturbed,
and are invisible to the casual searcher. However,
sifted leaf litter suspended in extraction devices (e.g.,
Berlese funnels, Winkler bags; Besuchet et al. 1987)
can produce a surprising number of ants. Character-
istic inhabitants are the well-known and diverse
genera Solenopsis, Pheidole, and Hypoponera (but
fewer species than in the lowlands), and less well-
known groups such as Stenamma, Adelomyrmex,
Lachnomyrmex, Dacetonini, Basicerotini, Crypto-
pone, Gnamptogenys, Proceratium, and Amblyopone.
The habits of these cryptic leaf litter ants are virtually
unknown, but a surprising number of them have been
named because of the work of Carlo Menozzi (1927,
1931a, 193lb, 1936).
Canopy ants. An ascent to the canopy in lowland for-
ests reveals ants teeming over the surfaces of trunk,
branches, and leaves. In contrast, the Monteverde
canopy, with its thick sleeves of epiphytes and canopy
soil, appears devoid of ants. Patient searching may
reveal the occasional worker of Procryptocerus or
Camponotus on leaf or branch surfaces. There is abun-
dant ant life in the Monteverde canopy, but one must
look in and under the epiphytes. Pulling back large
contiguous epiphyte mats reveals abundant but very
tiny ants living at the interface of branch surface and
epiphyte root mat. Colonies of these ants seem to have
no bounds. What appear to be continuous columnsof ants connect aggregations of workers, dispersed at
intervals of a few centimeters to a meter or more. Two
common ant species that look similar (a species of
Solenopsis and of Myrmelachista) share this habit.
Canopies of individual trees are dominated by one or
the other of these two species.
The Solenopsis nest almost entirely on branch sur-
faces, and the aggregations of workers contain larvae,
pupae, and one or more colony queens. They appear
to be "unicolonial," having multiple queens and no
well-defined colony boundaries. The Myrmelachista
occupy space on the branch surface and extend into
cavities inside the branches. The larvae and pupae are
concentrated in these branch cavities, rather than on
the branch surface. These branch cavities can be ex-
tensive, occupying many branches in the crown of a
tree. The food of these ants is unknown, but both spe-
cies tend coccoid Homoptera (mealy bugs and scale
insects). Homoptera are abundant along the ant paths
on branch surfaces and, in the case of Myrmelachista,
also inside the stems, on the walls of the branch
cavities.
Due to their prevalence across trees and their
abundance within trees, these ants must form a large
proportion of the animal biomass in these forests.
Their presence as major consumers, especially their
tending of plant-feeding Homoptera, suggests they
may have a major impact on nutrient transfer pro-
cesses in these forests. Their contribution to forest
biomass pools and nutrient transfer processes begs
for investigation.
Other Monteverde canopy ants have more discrete
nests and more clearly defined colony boundaries.
A common and conspicuous species is Pheidole
innupta. This large ant forms populous colonies in
large globose epiphyte mats. They are rarely seen on
the surface, and their feeding habits are unknown.
They are found by pulling open big epiphyte clumps
in the canopy, from which large numbers of black ants
emerge. They have weak stings and are no threat to
tree climbers.
A species in the Stenamma schmidti-complex
occurs in the cloud forest canopy. Nests occur under
small epiphyte patches, often on narrow branches.
The colonies are small, with no more than a few dozen
workers and a queen. This canopy species has a com-
plementary distribution with other members of the S.
schmidti complex, which are common in leaf litter on
the cloud forest floor. The schmidti-complex species
of the cloud forest floor are restricted to montane sites.
In contrast, the species from the Monteverde canopy
also occurs throughout Costa Rica in lowland wet
forests, where it occurs on the forest floor and not in
the canopy. This microhabitat shift with elevation
could be the result of competitive exclusion from135 Insects and Spiders