Anyone who has been outside and watched ants crawl by carrying leaves or balls of dirt or bits of food probably has realized that they are very strong creatures. Many of you have probably heard or read various figures saying that ants can carry X times their body weight with X being some rather large number. Previously scientists had believed that most ants could carry several hundred times their body weight. These estimations were made by watching what ants would carry but that isn’t a great way to determine the max amount that an ant can carry as it isn’t possible for scientists to know if the ant is carrying as much as it can or if it has no reason to carry more or if is just being lazy.
Researchers in the Ohio State Department of Mechanical and Aerospace Engineering weren’t happy with these estimations of how strong ants were and set out accurately measure the strength of ants’ necks and to figure out what makes them so strong. Unfortunately you can’t just ask ants to pick up a set of barbells so the team lead by assistant professor Carlos Castro had to come up with another solution. Their solution involved approaching the problem in a way similar to determining the strength of a material, you stress it until it fails. The scientists started by using electron microscopy and micro-CT machines to get up close looks at the interior and exterior of the ants in order to learn about the structure of their necks. After anesthetizing the ants so that they wouldn’t feel anything, the team then glued the ants heads to a piece of material which was placed into a centrifuge. As the centrifuge spun, the heads of the ants were held in place while their bodies were drawn outward. The faster the centrifuge spun, the more force was placed on the neck of the ant. The team kept increasing the speed of the centrifuge until the ants’ bodies were ripped from the head; at this point the scientists noted the speed of the centrifuge and used that to calculate the force that the necks could withstand before failing.
Castro and his team found that the ants’ neck joint started to stretch at a force of around 350 times their body weight and the necks ruptured at forces of between 3,400 and 5,000 times their body weight. This was much larger than previously had been believed and larger than the original estimate of 1,000 times their body weight that Castro and his team had figured before starting the experiment. While the whole experiment may sound rather cruel, it is important to note that the ants were anesthetized prior to going into the centrifuge; people also don’t tend to treat ants well in general as we normally tend to step on them or spray them with poison if we find them in our houses.
Of course the point of this study wasn’t just to figure out how strong the necks of ants are but also to figure out why they are so strong. This is where the imaging and x-raying of the ants came in as it gave Castro and his team the chance to study the structures of the neck. Electron microscopy showed that each part of the neck join was covered in different textures and had bumps or hairs extending from them. Other insects have similar structures and Castro theorized that they may play a role in the strength of the ants’ necks, saying “They might regulate the way that the soft tissue and hard exoskeleton come together, to minimize stress and optimize mechanical function. They might create friction, or brace one moving part against the other.”
The other major revelation from this study concerned the connection between the neck, which is made of soft material, and the head, which is made of hard material. In general transitions between very different materials can lead to a build up of stress and be a weak point in a design. Ants seem to deal with this problem by not having an abrupt transition between the materials; instead they have a gradual transition which may help eliminate the buildup of stress.
While these results are interesting and rather cool, they also serve a practical purpose and the fact that this research was undertaken by the Department of Mechanical and Aerospace Engineering should give some clue as to what that purpose is. Researchers hoped that by understanding what gave the joints in ants’ necks such strength, they could potentially build similar joints to dramatically increase the lifting strength of robots. Now of course engineers aren’t just going to go out and build giant robotic ants to use to carry things around, which is good as the potential of that turning out like a bad sci-fi/horror movie was very high. Instead, engineers hope to be able to mimic the aspects of ants that give them such strength, such as the microstructures and combination of hard and soft materials, to make stronger joints for robots. Even with these interesting results so far, there is still much work to do as researchers must figure out how to replicate these structures with artificial materials and how to scale them up to something larger than ant sized. Still, it is great to see that OSU is once again leading the way in cutting edge research that has the potential to improve the lives of everyone.