Invasive ants march on the West Coast

Invasive ants are generally a phenomenon of warmer climates. Argentine ants, red imported fire ants, and electric ants are all major economic problems in places like Florida, New Caledonia, and Australia. But what is to stop European and Asian ant species from damaging invasions of Canada? It turns out, not much.

Ken Naumann and Rob Higgins, entomologists working on ants in BC, have just published a paper in The Canadian Entomologist on the spread of Myrmica rubra, the so called European fire ant in coastal BC.

In many ways, European fire ants are typical Myrmica, engaged in scavenging, predation and aphid tending. They distinguish themselves in their high colony density and proclivity to sting.

This insect was first detected almost a century ago in Boston, and has since spread to many areas of eastern North America. It has not generally been problematic, but in the past 10-15 years, reports of high colony densities and spread have been increasing. These small red ants are superficially similar to other native Myrmica, but in occupied ground they reach staggeringly high colony densities of up to 4 nests/square metre. They become known to anyone walking on their turf due to their painful stinging attacks in defense of their nests. In areas with large numbers of colonies, activities as innocuous as sitting on the grass can become impossible.

Despite her beautiful wings, this Myrmica rubra queen will not fly, a strange trait that is ubiquitous across the North American range for this species.

One factor limiting the spread of these ants is that the queens do not seem to be able to fly. That trait has been lost in their transition to their new home, although the males still engage in winged dispersal. These ants are instead spreading through nest budding where already established and through movement of infested soil and wood into new areas.

In the paper, Naumann and Higgins report staggeringly high numbers of EFA captures in pitfall trapping in infested areas, compared to moderate numbers of native ants in uninfested habitats. The numbers of Myrmica rubra exceeded the numbers of all native ants by 10 to 1300 times!

In infested areas, Myrmica rubra is the only ant to be found.

More worryingly, Myrmica rubra seems to outcompete and eliminate all other native ants, and in infested areas, very few native ants can be found. In addition, other litter arthropods seem to be reduced in infested areas as well, though the reduction in species richness indices is mostly attributable to the loss of the native ants.

British Columbia, as a biologically diverse and relatively warm province with high levels of oceanic trade, may be the testing ground for biological invasions from ants. A second introduced Myrmica, Myrmica specioides, is also mentioned in the paper. Unlike M. rubra, Myrmica specioides queens retain their flight capabilities, and thus there is no feasible way of stopping their spread.

The ants are marching in BC, and entomologists are well advised to keep up with their movements!

Superficially similar, Myrmica specioides (left) can be distinguished in the field from M. rubra (right) by the sharp bend at the base of the scape. M. rubra has a gently curving scape instead.

Nowhere to go but up: Myrmica specioides queens are quite capable of flight!

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