other members of the schmidti-complex or the result
of adaptation to particular microclimatic conditions.
In cloud forests, the canopy is subject to greater ex-
tremes of temperature and dryness than the forest
floor (Bohlman et al. 1995). Perhaps microclimate
variables important to Stenamma make cloud forest
canopy and lowland forest floor more similar to each
other than either is to cloud forest floor.
Biogeography and geographic variation. History has
left its mark on the Monteverde ant fauna, with ele-
ments derived from both the north and the south. The
genera Stenamma and Cryptopone are Holarctic and
are increasingly restricted to the highlands as one
moves south in Central America. Stenamma fades out
in northern South America, and Cryptopone occurs
no farther south than Costa Rica. These are the ant
equivalents of the oaks (Quercus spp.), which show a
similar pattern. The remaining Monteverde ant gen-
era are widespread in the neotropics.
Species-level patterns in and near Monteverde are
complex, and parapatric distributions are common.
The lowlands to the west contain a Mesoamerican
fauna adapted to seasonal dry forest conditions. The
lowlands to the east contain a combination of South
American and endemic Central American elements
derived from South America and adapted to evergreen
rain forest conditions (Gentry 1982). Taxa from the
two sides may meet in or near Monteverde, as in the
case of the Eciton burchelli complex. The cloud for-
est also harbors montane specialists, for example,
Pachycondyla aenescens.
Cryptic ants of forest leaf litter often show bands of
discrete, parapatric "forms" that segregate by elevation.
Two morphologically distinct forms of Octostruma
balzani occur just east and west of Monteverde, but do
not occur in the narrow band of cloud forest that sepa-
rates them. A large dark form of Eurhopalothrix cf.
gravis occurs throughout the midelevation Atlantic
slope, up through the Monteverde cloud forest, and
down to the bottom of the evergreen belt on the Pacific
side. However, specimens from the narrow cloud for-
est strip on the ridge crest are subtly distinct from the
remainder. Neostruma brevicornis and N. myllorhapha
occur in the lowlands of Costa Rica, and both have
distinct forms that are larger and darker in Monteverde
and other cloud forest areas in Costa Rica. Cyphomyr-
mex salvini occurs as several distinct sympatric forms
in the lowlands, and a distinct, almost black form oc-
curs in the narrow strip of ridge crest cloud forest.
Discothyrea horni is found from Monteverde cloud
forest to sea level on the Atlantic slope, but in the low-
lands it co-occurs with a smaller, lighter-colored form.
Montane specimens of widespread species are of-
ten larger and darker than their lowland counterparts
(Brown 1959). Observations of ants in the Monteverde
cloud forest have corroborated this observation and
revealed that geographic variation of this kind can
be surprisingly discrete and occur over small spatial
scales. Monteverde is an ideal location for investiga-
tion of the contemporary ecological forces and the
historical processes driving character variation. It is
an excellent laboratory for the study of ant species and
speciation.4.7.6. Crawfordapis luctuosa,
a Ground-Nesting Bee of
the Central American Highlands
Gard Otis
A popular hiking destination of visitors to Monte-
verde is La Ventana at the Continental Divide, where
walkers encounter numerous holes 1 cm in diameter
scattered over the roadway and the cliff edge. A small
mound of dirt around them indicates that the inhabi-
tants have been actively digging. One is almost cer-
tain to see several large brown and black bees flying
slowly near ground level, then landing and entering
these holes. These are Crawfordapis luctuosa (Colleti-
dae: Diphaglossinae), which is known from the high-
lands of Central America from Chiriqui, Panama, to
Chiapas, Mexico. It was generally considered to be a
very rare bee until nesting aggregations were reported
along roadcuts in Monteverde (Otis et al. 1982) and
Chiriqui (Roubik and Michener 1985). The perma-
nently open nature of these roadcuts has allowed
them to remain as active nesting sites for up to 25
years (Roubik and Michener 1985). Large aggregations
with several hundred active nests and densities as
high as 21 nests/m^2 can develop, although this may
be an artifact of human disturbance. Prior to human
occupation, nesting was probably restricted to natu-
ral landslides that become overgrown with vegetation
within a few years.
A female Crawfordapis digs a nearly vertical tun-
nel into the ground to the surprising depth of 45-120
cm. Along the lower parts of this tunnel, she con-
structs lateral burrows 3-8 cm in length. At the end
of each lateral burrow, the tunnel rises slightly, then
turns downward to form a vertically oriented cell 33-
38 mm in length. The female works the surface of the
cell with fine clay, then secretes material that leaves
a shining, whitish, cellophanelike lining to the cell,
which is typical of this family. This lining functions
to keep water from the surrounding soil from enter-
ing the completed cell and to keep the soupy pollen
and nectar mixture brought by the female intact. An
egg is laid on the surface of the liquid food material,
after which the lateral burrow is filled in with soil.
The larva floats on the food during its development,136 Insects and Spiders