Cephalotes atratus – Gliding Ant

Cephalotes atratus – Gliding Ant

The tribe Cephalotini, to which these strictly New World ants belong, are strictly arboreal. These ants all nest inside of live or dead plant stems. They are commonly seen running up and down large tree trunks and within the crevices of bark.

Physiologically, they can be recognized by their heavily armored appearance and the fact that most are dorsoventrally flattened. Their integument is black with a dense covering of silvery scales, giving the body a silvery-gray appearance. Although they have such a tough-looking exterior, they are relatively unaggressive ants, often coexisting with and using the same runways as other more aggressive ant species.

The fact that they are dorsoventrally flattened is used as a means of passive defense, by the ants. When disturbed, they tend to stop and press themselves against the tree trunk or surface upon which they are running. Many may also rely on chemical defense that makes them distasteful to predators (Coyle 1966) and some even exude a foul odor which can be observed if you press their bodies with your finger.

Due to their chemical defense, animals come to recognize these insects and their distinctive appearance and know not to eat them. For this reason, more than 40 species of arthropods, including beetles wasps and true bugs, use a defense method known as ‘Batesian mimicry’. Batesian mimicry implies that a totally harmless species can imitate a toxic one in order to deter predators.

Cephalotes atratus colonies can reach over 10,000 workers but some colonies of Cephalotes, such as C. texanus can have only a few tens of workers.

Cephalotines are believed to be generalized omnivores or scavengers. They have been known to frequent extrafloral nectaries, to feed on bird droppings and various kinds of proteinaceous and sugar baits. A major component of their diet, however, is pollen, which workers harvest and feed upon (Andrade and Baroni Urbani 1999).

Cephalotes atratus were the first species of ants studied found to have the interesting behaviour of gliding. They are able to control and direct their fall from 30-40m in height. Now, at least five more genera of ants have been shown to have this same behaviour. All the species in the genus Cephalotes, that have been tested to date, have shown the ability to glide.

The reason the ants glide is that the likelihood of them falling to the ground, some 40m down, and surviving and finding their way back to their colony, is very low.  Either the fall will kill them upon arrival, either they will land, survive but be unable to find the pheromone trail back to the nest, or they’ll fall and land in the flooded ground, commonly found during the rainy season.

The fall process is executed with some 85% precision of landing successfully on the same tree. During their fall, the ants have been observed to reorient their bodies so their hind legs and abdomen point toward the tree. This means that they can make a 180-degree turn midair to land feet-first on the trunk. It’s not fully understood how they land but it’s believed that they have claws on the back of their legs that hook onto the trunk, allowing them to hang on.

Although they have a relatively controlled fall, the ants can fall at a velocity of 4m/s (12ft/s) and so sometimes, the ants may bounce off the tree trunk on the first try, but can usually successfully reorient themselves by making another 180-degree turn to try again.

It’s believed that the worker ants are secondarily wingless, meaning that their primitive forms were most probably winged. Once their wings were lost, they likely evolved the ability to glide the way they do now. The ability to glide is necessary for ants like Cephalotes, that forage at the outer reaches of branches as they are in greatest danger of being knocked off by wind gusts or passing monkeys. Interestingly enough, there is some evidence that these ants sometimes purposely drop off the tree to avoid predators, knowing that they can successfully glide back to their same tree.

References:

Andrade, M. L. de, and C. Baroni Urbani. 1999. Diversity and adaptation in the ant genus Cephalotes, past and present (Hymenoptera, Formicidae). Stuttgarter Beitrage zur Naturkunde Serie B (Geologie und Palaontologie) 271:1-889.

Coyle, F. A. 1966. Defensive behavior and associated morphological features in three species of the ant genus Paracryptocerus. Insectes Sociaux 13:993-104.

Longino, J.T. “The genus Cephalotes” The Evergreen State College. 27 June 2000. 3 July 2009.

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Longino, J.T. “Cephalotes atratus” The Evergreen State College. 27 June 2000. 3 July 2009.

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University of Chicago Press Journals. “When Industrious Ants Go Too Far.” ScienceDaily 1

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Sanders, R. Discovery of gliding ants shows wingless flight has arisen throughout the animal kingdom.” 9 February 2005. 3 July 2009.