The New Neotropical Companion

a relationship that apparently dates to about 50 million

years ago. Attine ants are largely restricted to the

Neotropics, where they are obvious to even the most

casual observer. Throughout rain forests, successional

fields, and savannas, well- worn narrow trails are traversed

by legions of ants of the genera Acromyrmex and Atta as

they travel (both diurnally and nocturnally) to and from

their underground colonies, bearing freshly clipped

leaves, and sometimes buds and flowers (plates 10- 34–

37). Their trails take them up into trees, shrubs, and vines,

where they neatly clip off rounded pieces of leaves to be

transported back to their underground colony. The ants

live in colonies of up to 8 million individuals, consisting

of a single large queen and myriad worker ants, most of

which remain subterranean. Workers are of several size

classes: very small (minima), medium- size (media), and

large (maxima). Soldiers, the principal defense class, are

large and well armed with formidable pincer jaws. Attine

colonies are underground, but mounds of displaced soil

and discarded leaves mark their multiple entrances on the

ground surface.

Leaf- cutters are somewhat selective as to which species

they clip. In Guanacaste, Costa Rica, one Atta species

clipped mature leaves from only 31.4% of the plant

species available. Another species used leaves from only

22% of the available plant species. The commonness or

rareness of a plant species has no correlation with Atta

preference. The ants may travel relatively far from their

colony to seek out a certain plant species. Internal plant

chemistry appears to influence Atta diet.

Plate 10- 34. Leaf- cutters, or fungus garden ants, marching with

their burdens of leaves are a common sight in the Neotropics.

Photo by Dennis Paulson.

Plate 10- 35. This photo of leaf- cutter ants shows size

distinctions among individuals. Photo by John Kricher.

Plate 10- 36. A prominent “highway” made by leaf- cutter ants as

they cross a field. Look carefully and note the small fragments

of leaves the ants are carrying. Photo by John Kricher.

Plate 10- 37. The aboveground part of an Atta ant colony. It

extends far below the surface. Notice a main trail on the right

side of the soil mound and the scraps of leaves on the mound,

and notice also that sapling trees are growing from the colony

mound. The ants make the soil uniquely fertile. Photo by John

Kricher.

chapter 10 tropical intimacy: mutualism and coevolution 175