The zombie-ant fungus is easily identifiable when its reproductive structure becomes apparent on its dead host, usually a carpenter ant. At the end of its life cycle, O. unilateralis typically generates a single, wiry yet pliant, darkly pigmented stroma which arises from the dorsal pronotum region of the ant once it is dead. Moreover, perithecia, the spore-bearing sexual structure, can be observed on the stalk, just below its tip. This complex forms the fungus’ fruiting body.

• Evans HC, Elliot SL, Hughes DP (September 2011). “Ophiocordyceps unilateralis: A keystone species for unraveling ecosystem functioning and biodiversity of fungi in tropical forests?”. Communicative & Integrative Biology. 4 (5): 598–602. doi:10.4161/cib.16721. PMC 3204140. PMID 22046474.
• Sung GH, Hywel-Jones NL, Sung JM, Luangsa-Ard JJ, Shrestha B, Spatafora JW (2007). “Phylogenetic classification of Cordyceps and the clavicipitaceous fungi”. Studies in Mycology. 57 (1): 5–59. doi:10.3114/sim.2007.57.01. PMC 2104736. PMID 18490993.

Most species within the O. unilateralis s.l. species complex have both a sexual (teleomorph) and an asexual morph (anamorph). These are different in terms of their function and characteristics. Generally, the asexual morphs identified for Ophiocordyceps are Hirsutella and Hymenostilbe, two genera of asexually reproducing fungi.

• Evans HC, Elliot SL, Hughes DP (September 2011). “Ophiocordyceps unilateralis: A keystone species for unraveling ecosystem functioning and biodiversity of fungi in tropical forests?”. Communicative & Integrative Biology. 4 (5): 598–602. doi:10.4161/cib.16721. PMC 3204140. PMID 22046474.

Morphological variation

O. unilateralis species exhibit morphological variations which are most certainly due to their wide geographic range, from Japan to the Americas. Moreover, it has been hypothesized that their morphological variations may also be a result of one fungus species maximizing its infection on one specific host ant species (host-specific infections). Different subspecies of ant can occur within the same area, which means that in order to coexist they have to occupy different ecological niches. Consequently, the fungi may have evolved at the subspecies level in order to maximize its fitness.

• Evans HC, Araújo JP, Halfeld VR, Hughes DP (June 2018). “Epitypification and re-description of the zombie-ant fungus, Ophiocordyceps unilateralis (Ophiocordycipitaceae)”. Fungal Systematics and Evolution. 1: 13–22. doi:10.3114/fuse.2018.01.02. PMC 7274273. PMID 32518897.

O. unilateralis core clade morphological characteristics

The O. unilateralis core clade, as described in 2018, has distinct morphological characteristics. It exhibits a single stroma with a Hirsutella asexual morph, which arises from the dorsal neck region of the dead ant and produces a dark brown perithecia attached to its stalk. These species are also recognizable through the host species they infect, which are only Camponotini species. Once the host is killed by the fungus, it is commonly found fixed through their mandibles onto the surfaces of leaves.

• Araújo JP, Evans HC, Kepler R, Hughes DP (June 2018). “Ophiocordyceps. I. Myrmecophilous hirsutelloid species”. Studies in Mycology. 90: 119–160. doi:10.1016/j.simyco.2017.12.002. PMC 6002356. PMID 29910522.

O. kniphofioides subclade morphological characteristics

The O. kniphofioides subclade, as described in 2018, also has distinct morphological characteristics. Its species produce a stroma that grows laterally from the host’s thorax which itself generates an orange ascoma. Moreover, species within this subclade share a Hirsutella asexual morph. As for the core clade, these species are also recognizable through the hosts they infect, which are usually neotropical ant species. The subclade does not present the same extended phenotype with the famous “death grip” that O. unilateralis species typically exhibit. Their hosts usually die at the base of large trees in the Amazonian rainforest, among the moss carpets.

• Araújo JP, Evans HC, Kepler R, Hughes DP (June 2018). “Ophiocordyceps. I. Myrmecophilous hirsutelloid species”. Studies in Mycology. 90: 119–160. doi:10.1016/j.simyco.2017.12.002. PMC 6002356. PMID 29910522.