Watch as a carpenter ant bites off another person’s injured leg in an attempt to save his life

Humans aren’t the only species that try to heal wounds – or even perform amputations. Some carpenter ants appear to treat their nestmates with wound cleansing or limb removal and may even adjust the course of treatment depending on the type of injury. The findings are described in a study published July 2 in the journal Current biology and observed in the video above.

“When we talk about amputation behavior, this is literally the only case in which a sophisticated and systematic amputation of an individual by another member of its species occurs in the animal kingdom,” study co-author and behavioral ecologist Erik from the University of Würzburg. Frank said in a statement.

For ants, wound cleaning is not exclusive to just one species. Megaponera analis ants use a special gland to release antimicrobial compounds intended to suppress possible infections. However, the Florida carpenter ants included in this new study do not possess these types of glands and appear to use only mechanical means to handle their fellow ants. This care has one of two routes. In the first method, the ants perform wound cleaning with their mouthparts, without the antibiotic-like secretions that other ants have. The second method involves a cleaning like the first, but is followed by complete removal of the affected leg with the mouth. To determine the best course of action, the insects appear to assess the type of injury.

In the studythe team analyzed two types of leg injuries: cuts to the femur and those to the ankle-like tibia. All femoral injuries were associated with initial cleaning of the incision by a littermate. A littermate then chewed the leg completely off. Shin injuries only received oral cleaning. In both cases, the ants with experimentally infected wounds had a much greater survival rate.

[Related: Matabele ants might be able to diagnose and treat infected wounds.]

“Thigh injuries, which always involved amputating the leg, had a success rate of about 90% to 95%. And for the tibia, where they did not amputate, it still reached approx [a] survival rate of 75%,” says Frank. This contrasts with survival rates of less than 40% and 15% for unattended infected femoral and tibial abrasions, respectively.

The team believes that the preferred route of wound care may be related to the risk of infection from the wound site. Micro-CT scans of the femur revealed that it is composed largely of muscle tissue. The muscle tissue suggests that the femur is a hemolymph–a part that plays a functional role in pumping blood from the leg to the main body. An injury to the thigh means that the muscles can become compromised and less able to circulate potentially bacteria-laden blood. However, the shin bone has less muscle tissue and is therefore little involved in blood circulation.

“In tibial injuries, the hemolymph flow was less obstructed, allowing bacteria to enter the body more quickly. With thigh injuries, the speed of blood circulation in the leg was slowed down,” says Frank.

Camponotus maculatus ants can clean wounds with their mouthparts. CREDIT: Danny Buffat.

Initially, it seemed that if damage to the tibia led to more rapid infections, amputation of the entire leg would be the most appropriate course of action. However, the team actually found the opposite. The speed at which the ants can amputate a leg makes a difference and an amputation with ants takes at least 40 minutes. For injuries to the tibia, the team’s experimental tests showed that if the leg was not removed immediately after the infection, the ant would die.

“Unable to cut the leg quickly enough to prevent the spread of harmful bacteria, ants try to limit the risk of fatal infections by spending more time cleaning the tibial wound,” study co-author and evolutionary biologist from the University of Lausanne. Laurent Keller said in a statement.

According to the teamThe fact that these insects can diagnose a wound and see if it is infected and then treat it makes it “the only medical system that can rival that of humans.”

Given the sophisticated nature of this behavior, it would be a logical next study to find out how these ants are capable of such precise care.

[Related: Invasive ants leave lions scrambling for prey on the savannah in an ecological chain reaction.]

“It’s actually all innate behavior,” says Keller. “Ant behavior changes based on an individual’s age, but there is very little evidence of any learning.”

The team is now conducting similar experiments in others Camponotus kind to investigate how conserved this behavior is and to find out whether all ant species that lack a special antimicrobial gland also perform amputation. Because the ant receiving care also facilitates the slow removal of a limb while conscious, the team hopes to further explore our understanding of pain in ant communities.

“If you watch the videos where you show the ant the wounded leg and let it bite off the other completely voluntarily, and then present the newly created wound for another to finish it [the] cleaning process – this level of innate collaboration is quite striking to me,” says Frank.