in large armies, killing and carrying off all the insects and
spiders that they find and sometimes attacking vertebrates. They have
been known to enter human dwellings, removing all the verminous insects
contained therein. These driver ants shelter in temporary nests made in
hollow trees or similar situations, where the insects may be seen,
according to T. Belt, "clustered together in a dense mass like a great
swarm of bees hanging from the roof."

[Illustration: FIG. 2.--Leaf-cutting and Foraging Ants. 1. _Atta
cephalus_; 2. _Eciton drepanophora_; 3. _Eciton erratica_.]

The harvesting habits of certain ants have long been known, the
subterranean store-houses of Mediterranean species of _Aphaenogaster_
having been described by J.T. Moggridge and A. Forel, and the complex
industries of the Texan _Pogonomyrmex barbatus_ by H.C. McCook and W.M.
Wheeler. The colonies of _Aphaenogaster_ occupy nests extending over an
area of fifty to a hundred square yards several feet below the surface
of the ground. Into these underground chambers the ants carry seeds of
grasses and other plants of which they accumulate large stores. The
species of _Pogonomyrmex_ strip the husks from the seeds and carry them
out of the nest, making a refuse heap near the entrance. The seeds are
harvested from various grasses, especially from _Aristida oligantha_, a
species known as "ant rice," which often grows in quantity close to the
site selected for the nest, but the statement that the ants deliberately
sow this grass is an error, due, according to Wheeler, to the sprouting
of germinating seeds which the ants have turned out of their
store-chambers.

Perhaps no ants have such remarkable habits as those of the genus
_Atta_,--the leaf-cutting ants of tropical America (fig. 2, 1). There
are several forms of worker in these species, some with enormous heads,
which remain in the underground nests, while their smaller comrades
scour the country in search of suitable trees, which they ascend, biting
off small circular pieces from the leaves, and carrying them off to the
nests. Their labour often results in the complete defoliation of the
tree. The tracks along which the ants carry the leaves to their nests
are often in part subterranean. H.C. McCook describes an almost straight
tunnel, nearly 450 ft. long, made by _Atta fervens_.

Within the nest, the leaves are cut into very minute fragments and
gathered into small spherical heaps forming a spongy mass,