Wasp Wednesday Week 8: Atta cephalotes (Linnaeus, 1758)

This week’s wasp is… a bit different than the previous weeks! My feature for this week is the leaf-cutter ant species Atta cephalotes! This species was first described by Linnaeus, the infamous taxonomist and founder of binomial nomenclature. This particular specimen was once part of a lab colony maintained at Drexel University which originated from Panama.

Wait – you might say – this is an ant! Why is it being featured for Wasp Wednesday? As it turns out, ants (which make up the family Formicidae) are wasps! Ants are an interesting case within the order Hymenoptera; like bees, ants are essentially never considered to be wasps in a vernacular sense. From an evolutionary perspective, ants are descended from an assemblage of wasps formerly known as the superfamily “Vespoidea”, which places them closely related to Vespidae (yellow jackets, paper wasps, and hornets) and many other groups of conspicuous stinging wasps. The exact reason for this lack of broader inclusion within “wasps” is somewhat uncertain, but it is likely because of their general differences in both morphologically and societal perception. Ants, like bees, just seem different, but they are indeed wasps nevertheless! Now, without further ado, let’s move on to the species profile!

Taxonomy: This species is a member of the family Formicidae, which contains the ants. A handful of other hymenopteran groups are sometimes referred to as ants, particularly the “velvet ants” of the family Mutillidae, but only members of Formicidae can be considered true ants. The ants are one of the most diverse groups within the order Hymenoptera, and currently includes over 12,000 described species worldwide. This diverse group has been very well studied from a taxonomic perspective, and is currently grouped into sixteen extant subfamilies. The genus Atta is placed in the subfamily Myrmicine and the tribe Attini, and currently contains seventeen described species.

Identification: For the most part, ants are easy to identify. The most commonly-encountered ants are female workers, which are mostly easily distinguished from other hymenopterans by their lack of wings. However, in the case of male ants (which are winged) or other wingless wasps, more-discrete characters are necessary to determine whether or not something is an ant. Luckily, these characters are more-or-less universal across all ants. The first of these characters is the antennae, which are elbowed. The antennae are formed from a long first segment and a series of smaller segments bent off the first at a distinct angle. The second useful character is the segmentation of the metasoma – the basal segments of the metasoma of an ant are node-like, and the remaining segments look like typical wasp metasomal segments. There are a handful of other characters that might be useful, but these listed here should be sufficient for separating most ants from other insects.

This species is separable from other ants by the presence of a pair of large spines on the pronotum, two pairs of spines on the promesonotum, and a distinct lack of tubercles on the gaster.

Natural History: Ants are eusocial organisms, which means they operate within a “society” – that is, each individual ant is part of a regimented hierarchy within its respective colony. Most species have a single female reproductive called the queen, female workers, and male reproductives. Members of the genus Atta are known as leafcutter ants, which are known for their habit of cutting off chunks of leaves and carrying them back to their nests.

Many species of leafcutter ants form “highways” on the forest floor; these are paths that the colony uses to transport leaf material. The ants are quite territorial of their highways – anything that invades their space may be subject to attack. Leafcutter ants cut leaf pieces in order to grow fungus on them, which then becomes the food source of the colony. This fungus is cultivated within the nest below the ground.

Interestingly, leafcutter ants appear to have evolved the tendency to constantly change food plants. This practice is likely greatly beneficial, as it prevents the ants from completely stripping the leaves from any given plant, which would almost certainly result in the plant’s death.

The species Atta cephalotes is found from Mexico all the way to Ecuador and Brazil, making it the most widespread species of leafcutter ant.

View This Species On:

iNaturalist: https://www.inaturalist.org/taxa/153974-Atta-cephalotes

AntKey: http://antkey.org/en/taxa/atta-cephalotes

Encyclopedia of Life: https://eol.org/pages/53197

References:

• Aguiar, A. P., Deans, A. R., Engel, M. S., Forshage, M., Huber, J. T., Jennings, J. T., … & Miko, I. (2013). Order Hymenoptera. In: Zhang, Z.-Q.(Ed.) Animal Biodiversity: An Outline of Higher-level Classification and Survey of Taxonomic Richness (Addenda 2013). Zootaxa, 3703(1), 51-62.
• Goulet, H., Huber, J. T. (1993). Hymenoptera of the world: An identification guide to families. Ottawa: Research Branch Agriculture Canada.