A recent study has revealed that liver fluke parasites, known as liver trematodes, have a more sophisticated strategy for infecting ants than previously thought. These worms lead ants to climb grass blades and then descend when the weather becomes too hot. The purpose of this manipulation is to increase the chances of ants being eaten by larger animals, allowing the worms to continue their life cycle.
Liver trematodes mainly live inside cows or other herbivorous ruminants as adults. The worms deposit eggs in the grass through the cow’s excretions, which are then eaten by snails. Inside the snails, the worms transition to the next larval stage and reproduce asexually. The snails react to the infestation by forming cysts around the worms, which are eventually expelled and ingested by ants along with the worm larvae.
Once inside the ant, the larvae enter their next life stage. Most of them migrate to the ant’s stomach, but one of them heads to the brain and takes control. The infected ant is then forced to climb to the top of a grass blade and attach itself, thus providing an opportunity for larger animals to eat the ant and the worms. The worms eventually reach adulthood in their final host, move to the liver, feed, reproduce, and lay eggs to restart the cycle.
A team of researchers from the University of Copenhagen decided to further investigate this complex process. They studied over a thousand infected ants in a forest in Denmark and found that temperature had the greatest influence on the ants’ behavior. The ants stayed on the grass during cool days but descended on hot days. This suggests that the worms manipulate the ants during the night and morning to position them on the grass when herbivorous animals are active, and then protect them from the sun during the day.
These findings highlight the complexity of parasite behavior and the need for further research to understand the specific mechanisms used by these worms to manipulate ant brains. While humans can occasionally become infected with liver trematodes, such infections are rare and humans are accidental hosts.
Sources: Behavioral Ecology