The first reports of red ants stinging people in Maine occurred from the late 1960s to the mid 1970s, but it was not until 1986 that the species was confirmed as M. rubra. Complaints received by the University of Maine Cooperative Extension office have increased sharply since 1998 [Groden el al. 2005]. Today M. rubra is considered a nuisance pest in most places where it is established in North America.
However, in Europe and northern Asia, where these ants are native, ants in the genus Myrmica are considered important for the conservation of rare Maculinea butterflies which live in association with the ants. Myrmica rubra in particular is considered to be a host for Maculinea teleius, M. nausithous, and two cryptic species of M. alcon [Elmes el al. 1998]. These butterflies are an important research topic due to their social-parasitic relationship with Myrmica ants and their importance as bioindicators of the health of Paleartic, and moist-grassland ecosystems in Europe [Mouquet el al. 2005].
[from Bolton el al. 2006]
In North America, M. rubra has been reported in Maine, Massachusetts, New York, Pennsylvania, New Jersey, Washington D. C., Rhode Island, New Hampshire in the US, and in Ontario, Québec, New Brunswick, and Nova Scotia in Canada [Groden el al. 2005].
Since 2001, entomologists at the University of Maine have conducted periodic surveys to determine the movement and the area colonized by the ant. In Maine, the ant is restricted to humid places along the coast. However, colonies have been reported at inland locations and there is a concern that the ant is capable of establishing in these new areas.
Workers of M. rubra are of a reddish-brown color, but the coloration greatly varies between individuals and colonies. Workers are small (4 to 5 mm), their "waist" has two segments, the head and the mesosoma are heavily sculpted, but the abdomen is shiny. The worker's body is cover with fine hairs. The antennae are 12-segmented with a four-segmented club and a bent scape. The 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. There are a few morphological differences that help to differentiate M. rubra from the other ants within the same genus. When viewed dorsally, the frontal lobes of M. rubra look thin and lamellar, laterally developed and do not cover the antennal base, and the propodeal lobes form a 90° angle apically (Francoeur, unpublished data).
In North America, M. rubra nests are cryptic and difficult to spot at first glance, as they do not construct obvious mounds from soil. Nests are usually in places that maintain high humidity for the colony including in the soil along roots of trees or shrubs, under rocks, logs or other human or natural debris, and in decaying logs. Their nest densities are extremely high in infested areas in the U.S., averaging between 0.5 and 1.5 nests per square meter, compared with 0.02 to 0.3 nests per square meter in its native habitat in England (Groden et al. 2005).
In Europe, nuptial flights occur during mid-August to mid-September depending on the latitude. Queens overwinter before laying eggs for the first time. Some queens overwinter alone, others as groups of newly mated queens, and some join an existing colony. In the following spring, queens search for food to begin reproduction. Queens that are part of a group have an advantage in foraging for food, and these queens will usually experience higher survival than solitary queens.
From egg hatch to egg production, queens take at least two years to start a colony. In Europe, M. rubra produces two types of brood characterized by the time necessary to mature. Rapid brood develops in the year that it is laid, but a slower brood will overwinter as third instar larvae and mature to adulthood the following year [Elmes el al.1998, Elmes el al. 1999].
In the United States, the situation is different. No nuptial flights have been reported, and new infestations appear to be caused by human-aided dispersal, particularly with the movement of infested soil, mulch, and potted plants. Colonies that are already established spread to adjacent areas via budding. This occurs when one or more queens and a group of workers, frequently with brood, move from an existing colony to a new nest site to form a satellite colony. Maine populations overwinter with slow brood (third instars), but it is not certain whether colonies produce rapid as well as slow brood.
Myrmica rubra infestations are particularly severe in many areas along the sea coast, lakes and streams. These are areas with high value for tourism. Home and business owners are concerned about the impact of these ants on their activities, income, and value of their property
In addition to its nuisance impact, M. rubra is also having significant effects on our natural ecosystems. M. rubra appears to be responsible for the reduction of the ant diversity, richness, and abundance in infested areas, and has also exacerbated populations of plant feeding hemipteran pests such as aphids and scales.
Cultural control. Another tactic is to make the environment less hospitable for this ant. These ants prefer high humidity, moist soil, reduced exposure to the sun (lightly shaded habitats). Reducing irrigation, mowing tall grasses and increasing sun exposure to the ground will decrease favorable nesting and foraging conditions for the ants. These ants build their nests under debris placed on the lawn, including rocks, boards, logs, and anything that maintains a moist environment underneath. Reducing nesting sites will reduce the populations and force the ants to nest elsewhere. This method will not eliminate M. rubra, but may help to keep population densities low.
Chemical control. If chemical control is necessary, the label of an insecticide labeled for ants should be followed precisely. Currently, the most effective materials to use are the food bait-based insecticides. Unfortunately, none of the insecticides screened by the Entomology program at the University of Maine have successfully eliminated these ant populations. Low concentrations (less than 1%) of boric acid mixed with a sugar attractant have been successful in the laboratory; however, results in the field have been inconsistent. Other control tactics are currently under evaluation.
For more information about the management of European fire ants, or any other pestiferous ants in gardens, yards, landscapes, or parks; please contact the local Cooperative Extension Service Office.
The authors thank Dr Frank Drummond from the University of Maine for his constructive comments to an earlier version of this manuscript, and to the University of Maine's Ant Team for their collaboration with the project.
Authors: H. Alejandro Arevalo, University of Florida; and Eleanor Groden, School of Biology and Ecology, University of Maine
Photographs: E. Groden, F Drummond and H.A. Arevalo, University of Maine
Project Coordinator: Thomas R. Fasulo, University of Florida
Publication Number: EENY-410
Publication Date: August 2007
Copyright 2007 University of Florida and University of Maine
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