Aeronautic ants

Gliding ant, Cephalotes atratus. Photo by Alex Wild of Myrmecos.

The Neotropical arboreal ant, Cephalotes atratus, is a species of gliding ant. These ants live rain forest canopies where the workers spend a lot of time on exposed branches and leaves. If one these ants accidentally falls, or intentionally leaps from a branch to avoid predation, it is able to glide adeptly back to a target tree trunk or branch. A video of this gliding behavior can be seen, here. As the ant falls, it turns itself over on its back and uses its head and appendages as rudders to steer itself backwards to a tree.

These ants possess obvious evolutionary adaptations to aid their gliding behavior. Namely, the top of their head is flattened in order to generate lift as they fall upside down. In addition, the terminal segment of their hind legs is elongated and flattened (see photo below). In order to determine the importance of these specialized leg structures in generating lift and steering during descent, researchers preformed a series of experiments on the ants. They excised various body parts and then dropped the ants from the forest canopy, recording their success in gliding back to a tree.

Left: Tarsal segment of C. atratus leg viewed from the top and the side showing flattened surface. Right: Percent success of gliding back to a tree from dropped ants with various excised body parts. Adapted from Yanoviak et al., 2010.

The first thing you should note from this experiment is how damn good these ants are at gliding back to a tree when they are dropped. The unmolested control ants on the right make it to a tree over 90% of the time. However, the researchers found that if the hind legs are removed, gliding success drops to 40%, making the hind legs the most crucial appendages for steering while gliding. Also, despite the removal of a single hind leg, the other legs, or the gaster, the ants still did a pretty decent job of getting back to a tree. This success in the face of adversity suggests that steering control is highly flexible and adaptable in these worker ants. Therefore, even if a limb is lost to a predator, they are still able to glide to safety.

This research sheds light onto the complex bio-mechanics of gliding ants. They are required to preform a tightly controlled set of maneuvers as they fall in order to generate directional gliding forces. This research has shown that several structural adaptations cooperatively assist in these maneuvers.

In addition, the study of arboreal ant gliding behavior may provide clued about the origins of insect flight. Though ants are highly derived, previous fossil evidence has shown that early hexapods may have glided before developing wings. Similar gliding phases are also hypothesized in the evolutionary history of winged vertebrates. Therefore, continued research into the aerodynamic forces at work in gliding ants may suggest clues regarding the necessary stepping stones in gradual evolution of animal flight.

More on gliding ants:

• Article about this research in The Guardian, here.
• Photographing gliding ants mid fall, at Myrmecos.
• The origin of insect wings, at Catalogue of Organisms

References:

• Yanoviak SP, Munk Y, Kaspari M, & Dudley R (2010). Aerial manoeuvrability in wingless gliding ants (Cephalotes atratus). Proceedings. Biological sciences / The Royal Society PMID: 20236974

Arthropod on arthropod violence

How does a swarm of army ants take down a heavily armored fresh water crab? Let’s find out…

That’s gotta be a pretty terrible way to go.

Red in mandible and pincer…

Arthropod Roundup: Crabzilla, altruistic ants, and neuronal recordings from Drosophila in flight.

Quick notes about recent Arthropod news and research:

• The National Sealife Centre in Birmingham, England is hosting a special guest, on loan from Japan. Meet ‘Crabzilla’, a not-quite full grown Japanese spider crab, Macrocheira kaempferi. Crabzilla has an impressive leg-span of about 10 ft, but members of this species can reach over 13 ft. By length, they are the largest know arthropods on the planet. You can read more about Crabzilla’s visit to the UK at the Daily Mail.
• New research on the ant species, Temnothorax unifasciatus, found compelling evidence of altruistic behavior. Altruism is commonly observed in social insects, as single individuals often sacrifice their energies or lives for the good of the colonial super-organism. In the present study, the researchers showed that ants infected with a deadly and contagious fungus would often leave the colony and die in seclusion. This prevents transmission of the disease to other members of the closely interacting colony. Read more at the BBC.
• Finally, researchers have developed new techniques for recording electrical signals from fruit fly neurons while the animals are in tethered flight. Fruit flies, Drosophila melanogaster are the go-to arthropod model organisms, and a plethora of molecular and physiological tools are available for studying any aspect of their biology. This new neuronal recording technique was applied to look at the activity of visual pathways in the brain during flight. The researchers found that the stimulus response time of the Drosophila visual system nearly doubles when the animal is in flight. This allows the flies to change direction rapidly mid-flight in order to avoid obstacles. This work was published in Nature Neuroscience. Read more at Science Daily.

  A tethered fruit fly in flight with a pink electrode in its brain. Photo by Gaby Maimon and Michael Dickinson.