Humans aren’t the only ones capable of performing amputations to save lives. Florida carpenter ants have been observed engaging in life-saving limb removal of their nestmates based on the location of their injuries, a new study reveals.
Researchers found that 90% to 95% of ants that underwent these amputations survived and continued their duties in the nest, despite losing a leg. The study, published in Current Biology, builds on previous research from 2023 by the same international team.
Earlier research identified that Matabele ants (Megaponera analis) use their mouths to secrete antimicrobial compounds to clean wounds and prevent infections. These compounds are produced by metapleural glands, which most ants possess. However, some species, including Camponotus floridanus (carpenter ants), have lost these glands over time. These arboreal ants, which live in trees, might be less exposed to pathogens than their ground-dwelling counterparts, explained lead study author Erik Frank, a behavioral ecologist at the University of Würzburg in Bavaria, Germany.
The pandemic led Frank and his team to shift their focus from Matabele ants in the Ivory Coast to the more accessible carpenter ants in their lab. They aimed to investigate how a species without antimicrobial compounds would treat wounds.
What they discovered was unexpected: carpenter ants perform a form of surgical intervention previously seen only in humans. Reddish-brown carpenter ants, about 1.5 centimeters long, often face injuries while defending their nests in the southeastern United States. The study’s coauthor, Dany Buffat from the University of Lausanne, first observed the ants cleaning wounds and performing amputations.
“The biggest surprise was that they perform amputations at all,” said Frank. “I didn’t believe it until I saw the videos myself.”
The ants only amputate limbs if the injury is on the femur (thigh). After biting off the leg, they clean the wound with their mouthparts, likely removing bacteria. For injuries on the tibia (lower leg), they only lick the wound intensively, resulting in a 75% survival rate.
To study this behavior, the researchers created controlled injuries using microscissors, then observed the ants’ responses. They found that untreated femur injuries had a survival rate of less than 40%, while untreated tibia injuries had a survival rate of less than 15%.
CT scans showed that the ants’ thigh muscles help circulate hemolymph, a fluid similar to blood. Injuries to the thigh impede circulation, slowing the spread of bacteria and making amputation effective. However, lower leg injuries don’t hinder circulation, so bacteria spread faster, making amputation less effective.
Ant-assisted amputations took about 40 minutes, which is likely why they opt for femur over tibia amputations, said senior study author Dr. Laurent Keller from the University of Lausanne.
The researchers believe this behavior evolved because it enhances colony productivity by saving injured workers. While the ants seem to diagnose and treat wounds expertly, Frank thinks their actions are instinctual, not conscious decisions.
Frank and his team aim to study wound care behavior in other ant species and across the animal kingdom to understand its evolutionary origins.
“We want to understand how ancestral wound care behavior looked and why some species opt for amputation while others use antimicrobial methods,” said Frank.