A new zombie ant behavior unraveled: Aggregating on tree trunks.

ABSTRACT

Hosts can be manipulated by parasites to move to locations advantageous for onward transmission. To investigate the role of behavioral manipulation in creating transmission hotspots, we studied the distribution of zombie turtle ants in the Amazon rainforest. The turtle ant Cephalotes atratus nests and mostly forages in the canopy, but is found at the base of trees when infected with the zombie ant fungus Ophiocordyceps kniphofioides. We found 626 infected cadavers on 14.8% of 162 trees sampled. Cadavers were highly aggregated on the surface of the trees, explained by behavioral observations indicating infected ants as slightly attracted to zombie ant cadavers on a tree. From 1,726 h of camera footage, we recorded the removal of three zombie ant cadavers by live ants. The number of removals compared to the density of infected individuals indicates the base of a tree as an escape from the evolved ability of social insects to recognize and treat disease inside the nest, allowing the parasite to continuously remain in the environment.