The full taxonomy of North American Aphaenogaster is only partially completed due to the genus’s complexity. The biggest challenge lies in the rudis complex because siblings are poorly differentiated (Fisher and Cover 2007). There are more than 195 known Aphaenogaster subspecies (Shattuck and Barnett 2001).
Description: Aphaenogaster rudis are foraging ants. They are medium to large in size, with about an average body length of 4mm. They have slender bodies, long legs, antennae and are reddish-brown (MacGown 2008).
Habitat: Aphaenogaster rudis are common throughout eastern North America and are typically found in lower elevations in mountainous or rocky habitats (MacGown 2008). They can be found in thickets, grassy habitats, pine barrens, and second-growth forests where they are often the dominant ant found on the forest floor, but less common by the forest edge (Ness and Morin 2008, and Fisher and Cover 2007) which may have more to do with the competition from rodents for seeds which the ants use to feed their larvae (Ness and Morin 2008). They are associated with eastern deciduous forests (Fisher and Cover 2007) where they can be found in small forest patches that have experienced low historical land-use (Mitchell et al. 2002).
Reproduction: A. rudis nests can be found in prairie areas and in forests. Their nests are relatively shallow and can be found in soil, beneath rocks, decomposed wood, fallen branches, and even in old cans and other trash found in forested areas. Typically, they nest inside decomposing wood and in between poison ivy vines and the base of a tree (Enzmann 1947). See picture on right for A. rudis nest.
The structure of A. rudis colonies are based on a single reproductive queen and sometimes up to 2,000 worker ants. Colony structure is primarily influenced by the number of worker ants. Also, A. rudis queen ants are fertilized by a single mating (typically occurring in late August) and therefore avoid the complications other ant colonies encounter with multiple queen matings (Morales and Heithaus 1998).
Mutualism in Action: A. rudis are great seed dispersers and many species of plants depend on them for seed dispersal. The process is mutualistic as the ants carry the plant seeds to their nests where the ant larvae eat the lipid-rich parts of the seed. The seed embryos are usually left unharmed and therefore able to properly germinate (Beattie 1985 in Morales). These ants are extremely effective seed dispersers because they carry the seeds away from the maternal plant and bury it in nutrient-rich nests where it can grow (Morales and Heithaus 1998). See picture below of adult aphaenogaster rudis feeding larvae. Also, A. rudis ants compete with small forest rodents for access to plant seeds; the relationship between the seeds and the forest rodents is based on predation because the seed embryo is killed.(Ness and Morin 2008).
Defense and Natural Enemies: Aphaenogaster rudis ants are both scavengers and predators. (Fisher and Cover 2007). They prey on worms, grub, adult insects and termites (“Follow the Pheromone Road.”). Aphaenogaster rudis are also extremely effective predators due to an efficient chemical found on the posterior of their body. The chemical paralyzes the prey while simultaneously leaving a pheromone trail. The pheromone trail attracts other ants for help in paralyzing and killing more challenging and violent prey. A. rudis is the only ant species to have been found that have this two-in-one chemical compound that is used to attract fellows ants and attack prey. The chemical is actually consisted of four different compounds, but all four compounds are necessary to successfully create the compound (“Follow the Pheromone Road.”).
Location of focal individual in the North Woods: Aphaenogaster rudis are less common on forest edges, perhaps due to predation and seed competition by small mammals (Ness and Morin 2008).
Hypothesis regarding this species that you could test with an experiment: What kind of forests and where in the forest do A. rudis thrive best in? (Old growth v. secondary growth or patches/fragmentation v. larger forests).
How affected/how reliant are forest plant species on the A. rudis ant? Reversely, how affected/how reliant are A. rudis ants on plant seeds for their larvae? Are there other sources of food for A. rudis embryos than plant seeds?
Enzmann, J. “Aphaenogaster rudis.” AntWeb. 1947. The California Academy of Sciences. 6 Apr. 2008 <http://antweb.org>. Fisher, Brian, and Stefan Cover. Ants of North America: A Guide to the Genera. California: University of California Press, 2007.
“Follow the Pheromone Road.” American Institute of Biological Sciences: Bioscience BioBriefs 48.4 (Apr. 1998). 6 Apr. 2008 <http://web.ebscohost.com>.
MacGown, Joe. Aphaenogaster rudis. Mississippi Entomological Museum. 6 Apr. 2008 <http://mississippientomologicalmuseum.org.msstate.edu>.
Marshall, Stephan. Insects: Their Natural History and Diversity.Buffalo: Firefly Books, 2006.
Mitchell C.E., Turner M.G., Pearson S.M. “Effects of Historical Land Use and Forest Patch Size on Myrmechores and Ant Communities.” Ecological Applications by the Ecological Society of America. (2002):1364-1377.
Morales, Manuel, and Raymond Heithaus. “Food From Seed-Dispersal Mutualism Shifts Sex Ratios in Colonies of the Ant Aphaenogaster Rudis.” Ecological Society of America 79.2 (Mar. 1998): 734-740. 6 Apr. 2008 <http://proquest.umi.com>.
Ness, J. H., and D. F. Morin. “Forest Edges and Landscape History Shape Interactions Between Plants, Seed-Dispersing Ants and Seed Predators.” Biological Conservation 141.3 (Mar. 2008): 838-847. ScienceDirect. 6 Apr. 2008 <http://www.sciencedirect.com>.
Shattuck, S.O and N.J. Barnett. "Australian Ants Online" CSIRO Australia. 2001. 22 Apr. 2008 <http://www.ento.csiro.au/science/ants/default.htm>.
Terrence P. McGlynn, Ryan A. Carr, Johnny H. Carson, Johnathan Buma. “Frequent Nest Relocation in the Ant Aphaenogaster araneoides: Resources, Competition, and Natural Enemies.” Oikos 106.3 (Sept. 2004): 611–621.