The Zombie Ant: Parasitic Fungi and Behavior Manipulation
Biology 342 Fall 2014
"The Zombie Ant"
In the tropical rainforests of southern Thailand, a strange spectacle occurs. After returning from a long day of foraging, a carpenter ant, Camponotus leonardi, wanders away from the comfort of its colony. The ant, in a “zombie-like” state, staggers, seemingly randomly, and convulses until it reaches a location about 25 cm above the forest floor where it then sinks its mandibles into the vein of a nearby leaf. Ultimately, the ant perishes. Death gives rise to birth, for within a few days a peculiar looking stalk grows out of the dead ant's head. When the stalk has fully grown, spores produced by the parasitic fungi are dispersed into the environment. A graveyard of ants that met a similar fate surrounds the corpse (Hughes et al., 2011; Andersen et al., 2009; Pontoppidan et al., 2009).
Figure 1. A "zombie ant" with a mature, healthy fruiting body sprouting from its neck. Source: David Hughes, Penn State University
These ants have been infected by the fungus Ophiocordyceps unilateralis. O. unilateralis manipulates the behavior of an ant, turning it into a mindless “zombie” that seeks an ideal location for fungal proliferation. This phenomenon has been observed in many locations, including South Carolina (Bekker et al., 2014) and Brazil (Evans et al., 2011).
The above occurrence of behavioral manipulation, however, is not unique to O. unilateralis and carpenter ants; fungi of the genus Ophiocordyceps parasitize many species of insects, including caterpillars and stinkbugs. This website explores the parasitic interactions between fungi of the genus Ophiocordyceps, with a focus on Ophiocordyceps unilateralis, and their host ants through the framework of Nikolaas Tinbergen’s four questions: Mechanism, Ontogeny, Adaptive Value and Phylogeny. For more information on Tinbergen’s four questions, click here.
A short clip showcasing Ophiocordyceps unilateralis was shown on BBC's Planet Earth. The clip can be viewed below. You can also go to BBC's official YouTube channel here to watch an extended and higher quality version.