I photographed these major workers of Weaver ants (Oecophylla smaragdina) as they were running up and down the laterite wall. I have used 5D SR coupled with Canon EF 100mm f/2.8L Macro IS USM with Canon MT-24EX macro twin light flash. Even though they were moving quite fast I was able to focus on them accurately using the camera. My older method with 5D mark II & III used to be to keep the lens in manual focus and then move the body forward and back till I get the focus I want. It was perfectly possible for a relatively slow subject but not on fast movers like these ants. This time I let 5D SR camera to auto focus and used AI servo mode. When I used a bunch of 5 or 9 focus point option the result was quite satisfactory. Camera was able to focus and follow the subject without any problem. I also used the focus limiting switch on the lens to concentrate on the near focus only rather than switching all through the focus.
Weaver ants (Oecophylla smaragdina) are eusocial insects of the family Formicidae of the order Hymenoptera. Weaver ants live on trees and are known for their unique nest building behavior where workers construct nests by weaving together leaves using larval silk. Colonies can be extremely large consisting of more than a hundred nests spanning numerous trees and contain more than half a million workers.
Like many other ant species, weaver ants prey on small insects and supplement their diet with carbohydrate-rich honeydew excreted by aphids. Oecophylla workers exhibit a clear bimodal size distribution. The major workers are approximately eight to ten millimeters in length and the minors approximately half the length of the majors. There is a division of labor associated with the size difference between workers. Major workers forage, defend, maintain and expand the colony whereas minor workers tend to stay within the nests where they care for the brood and ‘milk’ scale insects in or close to the nests.
Oecophylla smaragdina found in Australia often have bright green gasters. These ants are highly territorial and workers aggressively defend their territories against intruders. Because of their aggressive behavior, weaver ants are sometime used by indigenous farmers, particularly in southeast Asia, as natural bio-control agents against agricultural pests. Although Oecophylla weaver ants lack a functional sting they can inflict painful bites and often spray formic acid directly at the bite wound resulting in intense discomfort.
Weaver ant colonies are founded by one or more mated females (queens). A queen lays her first clutch of eggs on a leaf and protects and feeds the larvae until they develop into mature workers. The workers then construct leaf nests and help rear new brood laid by the queen. As the number of workers increases, more nests are constructed and colony productivity and growth increase significantly. Workers perform tasks that are essential to colony survival, including foraging, nest construction, and colony defense.
The exchange of information and modulation of worker behavior that occur during worker-worker interactions are facilitated by the use of chemical and tactile communication signals. These signals are used primarily in the contexts of foraging and colony defense. Successful foragers lay down pheromone trails that help recruit other workers to new food sources. Pheromone trails are also used by patrollers to recruit workers against territorial intruders. Along with chemical signals, workers also use tactile communication signals such as attention and body shaking to stimulate activity in signal recipients. Like many other ant species, Oecophylla workers exhibit social carrying behavior as part of the recruitment process, in which one worker will carry another worker in its mandibles and transport it to a location requiring attention.
The weaver ant’s ability to build capacious nests from living leaves has undeniably contributed to their ecological success. The first phase in nest construction involves workers surveying potential nesting leaves by pulling on the edges with their mandibles. When a few ants have successfully bent a leaf onto itself or drawn its edge toward another, other workers nearby join the effort. The probability of a worker joining the concerted effort is dependent on the size of the group, with workers showing a higher probability of joining when group size is large.
When the span between two leaves is beyond the reach of a single ant, workers form chains with their bodies by grasping one anther’s petiole (waist). Multiple intricate chains working in unison are often used to ratchet together large leaves during nest construction. Once the edges of the leaves are drawn together, other workers retrieve larvae from existing nests using their mandibles. These workers hold and manipulate the larvae in such a way that causes them to excrete silk. They can only produce so much silk, so the larva will have to pupate without a cocoon. The workers then maneuver between the leaves in a highly coordinated fashion to bind them together. Weaver ant’s nests are usually elliptical in shape and range in size from a single small leaf folded and bound onto itself to large nests consisting of many leaves and measure over half a meter in length. The time required to construct a nest varies depending on leaf type and eventual size, but often a large nest can be built in significantly less than 24 hours. Although weaver ant’s nests are strong and impermeable to water, new nests are continually being built by workers in large colonies to replace old dying nests and those damaged by storms.