Ants are in the family Formicidae. All ants are
eusocial (or derived from social ancestors in a few
parasitic species), meaning that they exhibit (1) re-
productive division of labor, with reproductive
queens and sterile or nearly sterile workers; (2) co-
operative care of the young; and (3) overlapping gen-
erations in the colony. Workers are female and wing-
less. Queens are differentiated from workers and
usually have wings that they discard prior to nest
establishment. Males are winged, with small heads
and large eyes, and usually do not look like workers
or queens. General treatment of ant biology is de-
scribed in Holldobler and Wilson (1990), and keys
to genera are in Bolton (1994). There are 80 genera
of ants in Costa Rica, of which 46 are known in the
Monteverde area.
Army ants (including Simopelto). The Ecitoninae are the
New-World army ants, comprising their own subfam-
ily (Bolton 1990). All Ecitoninae are group hunters,
usually taking exclusively live prey in massive raid-
ing parties (Holldobler and Wilson 1990, Gotwald
1995). Over 15 species of Ecitoninae are known from
Monteverde in the genera Eciton, Labidus, Noma-
myrmex, and Neivamyrmex. Although army ants are
a diverse group, almost all behavioral and ecological
studies have focused on one lineage, the Eciton bur-
chelli complex.
Eciton burchelli subspecies parvispinum is the
most common army ant in the Monteverde area.
Workers hunt in large swarm raids during the day and
commonly enter houses during raids. In swarm raids,
the ground is blanketed with a dense layer of work-
ers. This layer of ants is up to 4 m wide and 2 m front
to back, and slowly moves across the ground, flush-
ing suitable prey that are then captured, dismem-
bered, and moved back to trunk trails that lead rear-
ward from the raid front. Colonies exhibit endogenous
activity cycles and synchronized brood development
often described for army ants (Holldobler and Wilson
1990, Gotwald 1995). They alternate between statary
phases (remaining in one nest site) and nomadic
phases (moving to a new nest site each night). During
the statary phase, the queen lays a mass of eggs that
hatch at the same time and grow as a cohort of lar-
vae. As food demands of the colony increase due to
the growing larval cohort, the colony enters the no-
madic phase, moving to fresh hunting grounds each
day. When the larvae begin to pupate and food de-
mands decrease, another statary phase begins. Dur-
ing the nomadic phase, the temporary nest sites are
often located between tree buttresses, against dead
logs, or in other exposed situations. At this time, one
can observe prominent bivouacs: globular masses of
ants that form the living walls of a nest.
Species of the genus Labidus also swarm raid.
Swarm raiding species of Labidus have generally
black workers that are on average smaller than Eciton
workers, and thus the swarm raids appear more dense.
I have seen some spectacularly large Labidus swarms
crossing the dirt roads of Monteverde—they look like
broad bands of black paint. Labidus coecus is a
species with shiny, dark red, strongly polymorphic
workers. It is fairly common even in urban areas and
occurs from Texas to Argentina. They are largely sub-
terranean (Perfecto 1992) but will come to the sur-
face to feed at localized food sources; these short for-
ays can take the form of a swarm raid. They are more
omnivorous than other army ants and will gather
kitchen scraps. Army ants that do not swarm raid,
although diverse, are less conspicuous. They hunt
exclusively in files and are often nocturnal or subter-
ranean. In Monteverde, they include four additional
Eciton species, two Nomamyrmex species, and at least
four species of Neivamyrmex.
The genus Simopelta is a convergent army ant (Got-
wald and Brown 1967) in a different subfamily, the
Ponerinae. As with army ants, they have group-raid-
ing workers with reduced eyes, synchronized brood
development, and an enlarged, wingless queen that
looks remarkably like an army ant queen. They have
black, weakly polymorphic workers, and in the field
their slow-moving columns look like those of another
common cloud forest army ant, Neivamyrmex su-
michrasti. They are relatively common in primary
forest in the 500-1500 m band on the Atlantic slope
but appear to be absent from the lowlands. There may
be as many as five species in the Monteverde area.Fungus-growing ants. The fungus-growing ants com-
prise the tribe Attini. These ants harvest substrates on
which they culture fungi, and the fungi provide the
food for the colony. Attines vary widely in worker
size, colony size, and fungal substrate. The conspicu-
ous leafcutting ant genera are Atta and Acromyrmex.
These ants cut and harvest leaf fragments for their
fungal substrate (Fig. 4.17). Other genera of Attini
have smaller workers that are not conspicuous leaf-
cutters. Instead, they harvest caterpillar droppings,
dead insect parts, or other nutrient-rich substrates for
their fungi (Holldobler and Wilson 1990).
There are two leafcutting ant species in the Monte-
verde area. Atta cephalotes is a big leafcutting ant of
open pastures in lower Monteverde. Colonies of Atta
can be enormous, with over a million workers. Nests
are a voluminous system of subterranean galleries,
with a superstructure of bare excavated soil that may
be meters across. Acromyrmex coronatus is a small
leafcutting ant and is a major pest in gardens. It will
come into houses at night to gather food that has been133 Insects and Spiders