Social Carrying in Weaver Ants

While photographing for the last blog on weaver ants I observed one of the weaver ant worker was carrying another worker in its mandible. This bares the question as to why? Are these individuals being carried lazy or are they injured or even dead? The answer is none of these but is in fact that their actions are called “social carrying behaviour”.

Apparently, this behaviour I had the chance to witness is common among different species of ants. The ‘carriers’ are workers from the same nest who carry one another, usually when moving to a different nesting site. Like many other ant species, Oecophylla workers exhibit social carrying behaviour 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.

Predominantly to transport one another, as well as the eggs, larvae and pupae to different nest sites, this behaviour is observed across most ant species. Transporting the most vital member of the colony, the Queen, has to be carried out in a very tactical manner so she does not come into any danger or appear vulnerable. The Queen is generally carried in the middle of the nest emigration so that she has the support of half the colony on either side of her.

Generally, once a new nest site has been found half the colony will go to build it whilst the other half stay to tend to the eggs, pupae and larvae before relocating them. In weaver ant colonies in particular, the Queens body is completely covered by guards whilst emigrating, to disguise her and to eliminate any attempts of her demise by ant rivals. It has been found that within a colony only a specific group of ants will organize nest emigrations and these will be the carriers that recruit other ants to new nest sites. Interestingly, it was observed in studies that the carriers had completely undeveloped ovaries compared to those being carried who had well developed ovaries and were therefore the reproductive females of the colony.

Adult nest-mates carry each other for several reasons. But the most common is when the colony, or parts of the colony, move from one nest site to another as a means of transportation. Like the rest of the tasks in that complex society, carrying behaviour is a recruitment technique and an essential component of the division of labour ideology they adopt and actually thrive at.

Scientists have been able to study social carrying behaviour in several different ant species. What they found is that different species can have a different style of carrying adult nest-mates.

Ants from the genus Pseudomyrmex, for example, carry an adult mate by grabbing it by the base of the mandibles (mouthparts) as it curls up onto the back of the carrying individual. The eyes of the carried one face forward in such position, and this style is called the “Parasol-Posture”. There is a name for that too.

The carried individual may be also be grabbed by the base of the mandibles, though it is positioned upside-down and curls up under the ventral side of the carrier’s head. In the ant subfamily Myrmeciinae, adult transport is not stereotyped; workers gasp others from any part of the body and drags them over the ground, casually. In other cases, the transporter ant simply grasps the nest-mate from a leg or any other part of the body, lifts it up, then carries it away.

Here in these photos we see a method which the carrier ant has grabbed the nest-mate by the neck and this is a very common method of transporting male ants, though here it is the fellow worker ant who is carried away. Study has found that a specialized group of nest movers exists and is important in leading a colony in a relatively short period of time from unfavourable to favourable nest sites. They also found all these moving specialist ants have completely reduced ovaries, whereas many of the carried have well developed ovaries.