Scientific Method / Science & Exploration

Ants catch giant prey using “natural Velcro”

Using the same principle as Velcro, members of one ant species can hold onto …

Velcro helps astronauts sleep in zero-gravity space, assists those of us who don’t know how to tie our shoes, and makes for some very entertaining TV. But according to a new paper in PLoS ONE, a species of ant in French Guiana also uses the principles behind Velcro to catch prey that would otherwise be far too heavy.

Azteca andreae ants have a symbiotic relationship with two species of Cecropia trees, C. obtusa and C. palmata. The trees provide the ants with nectar to eat and cavities in which to live, and the ants protect the trees from leaf damage by catching and eating herbivores. 

The ants have a particularly interesting method of prey capture: they line up along the undersides of the leaves and lie in wait until insects land on the top of the leaf. Worker ants then chase the prey to the edge of the leaf, where it is ambushed by the hidden ants beneath.

Usually, an ant catches prey in its huge mandibles, then flips it under the leaf and hangs onto it as nearby workers swarm to relieve the ambusher of its heavy catch. The video provided by the authors is pretty amazing—definitely worth a look.

Velcro means bigger dinners

The discovery of "biological Velcro" resulted from a simple observation: groups of ants that lived on C. obtusa trees were more adept at catching heavy prey than groups that lived on C. palmata trees. 

Since the ants were all the same species, the difference had to be related to the leaf surface. It turns out that the underside of C. palmata leaves is relatively smooth, while C. obtusa leaves have a velvet-like covering thanks to an increased number of tiny, hair-like trichomes.

A. andreae ants have hook-like claws and can hang onto these downy trichomes just as the hooked layer of Velcro sticks to the fuzzy layer. When a particularly heavy prey item is dangling from the ant’s jaws, this “hook-and-loop” system means the difference between catching a big meal and letting the prey fall to the forest floor, where it escapes.

With the help of this natural Velcro, the ants are able to catch up to 13,350 times their own weight, and probably more. In contrast, other known species of symbiotic ants can hold less than 2,000 times their own weight. 

The largest catch the authors observed was a 10.5cm locust weighing 18.6g; bear in mind that each A. andreae ant weighs about 1.4mg (less than the average grain of sugar).

Can one ant hold a coin?

The ambitious researchers didn’t stop with observation, however—they wanted to experimentally check that their observations held up. So, how did they test whether this fuzzy trichome layer makes the difference? By hanging weights from the ants' mandibles, naturally.

The authors tricked the easily agitated ants into grabbing threads connected to objects with different weights, such as a 10-cent Euro coin.

The ants were in fact much more successful in capturing the objects—especially the heaviest ones—when they hung from the undersides of leaves, compared to either the upper sides of the leaves or to sheets of plastic. 

Additionally, the ants could hold far more weight for a longer period of time on C. obtusa leaves than they could on C. palmata leaves. The combination of the ants’ hooked claws and the leaves’ thick trichome layer gives these ants a distinct advantage when catching very heavy prey.

This scenario isn’t the only example of naturally occurring Velcro. Velcro was first inspired by burdock seeds, which have hook-like extensions that cling to the fuzzy hair of mammals during dispersal.

PLoS ONE, 2010. DOI: 10.1371/journal.pone.0011331  (About DOIs).

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