[Invasive Pests] The European Fire Ant Emerges in Massachusetts

When pest management professionals hear the words "invasive fire ant species," New England is generally not the area of the country from which they expect to hear these reports. But news that a pair of yards in a Cambridge, Mass., neighborhood were invaded in late July by Myrmica rubra, the European fire ant, serves as a reminder that the Northeast is susceptible to this troublesome invader.

George Williams, general manager and staff entomologist for Environmental Health Services, Norwood, Mass., says Myrmica rubra has been in New England for more than 100 years, but the reports from Cambridge have refocused attention on this pest.

"Up until literally right now this ant was not a problem for homeowners. They are usually found in grassy, marshland areas," Williams said. "In the case of (the Cambridge properties) the ants were spreading aggressively on the properties, in areas where children were playing, in the garden and under the deck."

It’s believed the Myrmica rubra in Cambridge hitched a ride in hostas that a neighbor brought back from Maine. Williams and Harvard University Entomologist Gary Alpert, Ph.D, have been studying this recent outbreak. Alpert told WBZ-TV that the area could experience what he calls a second wave that "is probably unique for Massachusetts."

Alpert also told WBZ -TV that once the females mate, they drop their wings and travel to a new nest, spreading from one yard to the next. "Think of it like a cancer. It doesn’t metastasize, it’s like one big tumor that just keeps spreading and spreading and spreading."

There are several important behavioral differences between Myrmica rubra and the red imported fire ant (Solenopsis invicta) — which is the invasive fire ant species most prevalent throughout the U.S. For example, Solenopsis invicta will construct complex mounds, whereas Williams says there is "no rhyme or reason" for how Myrmica rubra will behave on a property.

"Carpenter ants, for example, will forage along trails, while (Myrmica rubra) will be found everywhere throughout a property — in bushes, up in trees, under stones, in railroad ties, rock walls, open lawn areas, under patio blocks, etc. In instances with supercolonies it will appear as if ‘the ground is moving.’"

In terms of identification, Myrmica rubra is a two-node ant that is reddish-brown in color. In addition to having the ability to sting, another important distinguishing feature is Myrmica rubra’s propodeum (the first abdominal segment fused anteriorly to the thorax) has two spines pointing backwards, which is one of the main differences with other native ants (not of the genus Myrmica) in the northeastern U.S., according to the University of Florida Department of Entomology website.

Williams said baits show the greatest potential for controlling Myrmica rubra, however there are several challenges with baits. "We are not sure of the efficacy of commercially available brands as sugars are consumed by workers whereas proteins go to the queens."

Williams said that there are no current fire ant baits registered for use in Massachusetts. "Broadcasting granular baits would pose the easiest application method vs. liquid and gel formulations since the application area is expansive and placement baiting outdoors would be labor intensive," he said. "I would expect the non-repellent liquid products to work well on this species; however, this is not a low-impact application as non-target and beneficial insects are at risk due to the propensity of Myrmica rubra to forage on foliage, lawns and trees."

Williams and Alpert will be conducting a baiting study that they hope will shed additional light on the best ways to treat Myrmica rubra.

The author is Internet editor and managing editor of PCT and can be contacted at bharbison@gie.net.
 

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European Fire Ant

Myrmica rubra Linnaeus

Subfamily Myrmicinae

Color: Reddish-brown

Size: 1/8 to 3/16 inch

DISTRIBUTION

This species is widely distributed in Europe and was likely introduced into the northeastern U.S. in the early 1900s in imported plant materials. It has become a nuisance pest along coastal Maine and is also reported in New York, New Hampshire, Massachusetts, Pennsylvania, New Jersey and parts of southeast Canada.

KEY POINTS

Where they occur, Myrmica rubra are a health concern due to the painful stings they can inflict. Stings occur when people are outside enjoying their yard or a park or when gardening and disturb the workers or the colony. This ant also may impact the biodiversity in areas where it becomes established, outcompeting native ant species and attacking small animals.

Colony Structure. The colonies are moderate to large in size and contain multiple queens (polygynous). A colony may contain more than 20,000 workers and 600 queens. Colonies are also polydomous with multiple, interconnected nests.

Nesting Habits. A key factor in nest site location seems to be high humidity so nests are typically located under woody debris and leaf litter that retain moisture. Nest densities can be high with up to 1.5 nests per square meter. Like many pest ants, the colonies are highly mobile and quickly can be moved to areas with better resources. Nests are also possible in the soil of potted plants.

Foraging Behavior. Little is known about this species’ foraging behavior.

Feeding Habits. These ants are omnivorous, feeding on dead insects and the honeydew produced by homopterous insects (e.g., aphids, mealybugs and scale insects).

Colony Propagation. New colonies are formed by swarming reproductives. In the U.S., mating flights likely occur in late summer.

Source: PCT Field Guide for the Management of
Structure-Infesting Ants, Third Edition