Social insects, live in susceptible environments, are thought to prevent to the infection by allogrooming due to improve the survivorship. A function of allogrooming is thought to remove debris and entomopathogenic fungal spores on body surface. However, little is known about the effectiveness and efficiency of grooming behavior to improve the survivorship.

Here we examined how the effectiveness and efficiency of allogrooming increased in high risk of infection, using the ant Lasius japonicus exposed to the fungus Metarhizium anisopliae. As a result, we found that fungal spores in two workers decreased faster than in isolated worker. Additionally, we showed the rate of allogrooming to abdomen increased in the highest fungal spore concentration and the ratio of allogrooming to head decrease in the same spore concentrations, nevertheless the rate of self-grooming to each body parts and the rate of allogrooming to thorax did not change with fungal spore concentrations. Our results suggest that allogrooming remove fungal spores to compensate for the lack of self-grooming. This study illuminates how ants efficiently groom nestmates to remove the fungal spore on their body surface.