Dorylus, also known as driver ants, safari ants, or siafu,
is a large genus of army ants found
primarily in central and east Africa, although the range also
extends to southern
Africa and tropical Asia.
The term siafu is a loanword from Swahili, and is
one of numerous similar words from regional Bantu languages used
by indigenous
peoples to describe various species of these ants. Unlike the New World members of
the former subfamily Ecitoninae (now Dorylinae), members of this
genus do form temporary anthills lasting
from a few days up to three months. Each colony can contain over 20
million individuals. As with their New World counterparts, there is a soldier
class among the workers, which is larger, with a very large head and
pincer-like mandibles.
They are capable of stinging,
but very rarely do so, relying instead on their powerful shearing jaws.
Life cycle
Seasonally,
when food supplies
become short, they leave the hill and form marching columns of up to 50,000,000
ants, which are considered a menace to people, though they can be easily
avoided; a column can only travel about 20 metres in an hour. It is for those
unable to move, or when the columns pass through homes, that there is the
greatest risk. Their presence is, conversely, beneficial to certain human
communities, such as the Maasai, as they perform
a pest prevention service in farming communities, consuming the majority of
other crop-pests, from insects to large rats.
The characteristic
long columns of ants will fiercely defend themselves against anything that
attacks them. Columns are arranged with the smaller ants being flanked by the
larger soldier ants. These automatically take up positions as sentries, and set
a perimeter corridor in which the smaller ants can run safely. Their bite is
severely painful, each soldier leaving two puncture wounds when removed.
Removal is difficult, however, as their jaws are extremely strong, and one can
pull a soldier ant in two without it releasing its hold. Large numbers of ants
can kill small or immobilized animals and eat the flesh. A large part of their
diet is earthworms. All Dorylus species
are blind, and, like most varieties of ants, communicate primarily
through pheromones.
In the mating
season, alates (winged
drones, queens of real driver-ant species do not grow wings) are formed. The
drones are larger than the soldiers and the queens are even larger. Real driver
ants do not perform a nuptial flight, but mate on the ground, and the queens go
off to establish new colonies. As with most ants, workers and soldiers are
sterile (non-reproducing) females.
Male driver ants,
sometimes known as "sausage flies" (a term also applied to males of
New World ecitonines) due to their bloated, sausage-like abdomens, are among the
largest ant morphs, and were originally believed to be members of a different
species. Queens are even larger. Males leave the colony soon after hatching,
but are drawn to the scent trail left by a column of siafu once they reach
sexual maturity. When a colony of driver ants encounters a male, they tear its
wings off and carry it back to the nest to be mated with a virgin queen. As
with all ants, the males die shortly afterward. After that, the queen ant will
lay first eggs. Driver ant queens are able to lay up to 1,000,000 eggs per
month.
Such is the
strength of the ant's jaws that, in East Africa, they are used as natural,
emergency sutures.
Various East African indigenous tribal peoples (e.g. Maasai moran), when
suffering from a gash in the bush, will use the soldiers to stitch the wound by
getting the ants to bite on both sides of the gash, then breaking off the body.
This use of ants as makeshift surgical staples creates
a seal that can hold for days at a time, and the procedure can be repeated, if
necessary, allowing natural healing to commence.
Several species in
this genus carry out raids on termitaria, paralysing or
killing some of the termites and carting them back to the nest.
Colonies of real
driver-ant species have only one queen. When she dies, the surviving workers
may try to join another colony, but in other cases, when two colonies of the
same driver-ant species meet, they usually change the marching directions to
avoid conflicts.
In Popular Culture
Driver ants are
mentioned in the movie Indiana Jones and the Kingdom of the Crystal Skull,
where they are shown attacking, killing and presumably consuming a fully grown
man. In reality, while there are recorded cases of driver ants attacking
infants and immobile persons, deaths of healthy adults have never been
recorded. In addition, the supposed location in the film, the Amazon valley, is
not remotely within the driver ant's range.