Naumann, K., Moniz De Sa, M., Lewis, E. & R. Noronha. 2017. Supercolonies of an invasive ant, Myrmica rubra (Hymenoptera: Formicidae) in British Columbia, Canada. Journal of the Entomological Society of British Columbia 114:56-64.
Myrmica rubra, an ant species native to northern Europe and western Asia, is invading North America with unbridled success thanks to its supercolony-forming strategy. The first documented occurrence of this species in North America was in Massachusetts in 1908, over a century ago. It has become a nuisance over the last 10 years as populations have spread across northeastern North America and the Pacific Northwest. Invasive ants not only outcompete and eventually displace native ant species, they can also cause conflict with humans because they tend to be aggressive and can inflict painful stings. Populations of M. rubra that have established in southwestern British Columbia have taken over this region, essentially eradicating native ant species.
Clique behavior backed up with genetics
Naumann et al. conducted a study on colonies of M. rubra across seven regions of southwestern BC to determine if ants from these colonies were related to each other, functioning as larger supercolonies. The research team used both behavioral experiments and genetics to determine relatedness between colonies from different regions. Ants are able to identify unrelated intruding ants from different colonies by the chemical signature individuals ants carry on their body and respond aggressively to intruders. Multiple ant individuals were collected from various colonies across the seven regions and brought to a laboratory where individuals from two colonies at a time were placed in an arena for 10 minutes to observe how they interact with each other. The same behavioral experiment was also conducted with colonies from within two of the largest regions (Sea Island and Fraser River Park) to determine the relatedness of colonies within these larger areas. Genetic analyses were conducted for collected ant individuals to confirm relatedness results from the behavioral experiments.
The supercolony strategy
Naumann et al. suspect that the reason why M. rubra is such a successful invader of North America is that it could be forming supercolonies. Supercolonies are groups of ant colonies of the same species that exist cooperatively and can thus dominate territory across a larger area than if colonies functioned as their own individual units. Species that form supercolonies can outcompete other species for food and habitat through aggression and sheer numbers. Myrmica rubra is clearly dominating the regions it has invaded in BC, representing nearly 100% of the total abundance of ants collected in invaded areas. This species has even affected other insects and arthropods, reducing their numbers as well. Myrmica rubra also comes with a painful sting, which is a unique characteristic among the native ant species in BC.
At least two supercolonies have taken over BC
The results of the study indicate that there are at least two supercolonies of M. rubra inhabiting the seven regions of southwestern BC. This, however, is a conservative estimate. The genetic data indicated an overall lack of diversity among all collected ant individuals, although two genetically different groups did emerge from the phylogenetic analysis. According to these results colonies from Fraser River Park can be separated into either of these two groups, meaning that this region is not occupied by just one supercolony. The results of the behavioral experiments demonstrate different results, where five out of seven of the studied regions contain their own supercolony based on aggression between colonies from these regions. One supercolony spans several kilometers and thousands of nests in Sea Island.
Supercolony formation is the key to success
The ability of M. rubra to form supercolonies in the areas it has invaded has led to the accumulation of extremely high densities of this species. This will be a problem as this species expands its territory into human-occupied areas. It will become more difficult to avoid encountering these ants and potentially inciting their sting. Invasion by M. rubra has already decimated populations of ant species native to BC, which will impact the ecosystems that are dependent on the roles these ants play. Supercolony formation is usually only seen in invasive ant species like M. rubra. They are better able to find and remove food sources around their territory and also demonstrate greater aggression and higher activity levels in general. A lack of aggression between ants from different nests within the same supercolony also allows for a greater energy investment into foraging rather than defending territory from neighboring colonies. We can stop supercolonies from expanding from one region to another by reducing introductions of M. rubra into new areas via transportation of plant nursery products.