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An ant known for some years as Nylanderia sp. nr. pubens (but apparently really N. fulva, see below) is an invasive species that has developed into a serious nuisance in the southeastern United States. A rapidly expanding range, explosive localized population growth, and difficulty controlling populations have made this ant a significant pest.

Nylanderia pubens (formerly known as Paratrechina pubens; LaPolla et al. 2010), the Caribbean Crazy Ant, was reported to be relatively common in southern Florida during the mid-20th century (the name "crazy ant" for this group of ant species is inspired by their quick and apparently erratic movements). Similar pest ants in Florida (and the Caribbean) have been tentatively referred to as N. pubens or N. sp. nr. pubens (i.e., similar to, but not necessarily actually the same species as, N. pubens).

In 2002, an explosive population outbreak of an ant in the genus Nylanderia was documented around Houston, Texas (in 2010 this ant was reported from Louisiana and Mississippi as well). These ants were morphologically similar to N. pubens and the closely related N. fulva. Because of taxonomic uncertainty, they were designated as Nylanderia sp. nr. pubens (Meyers 2008). In the popular media, this Texas ant was called the Rasberry Crazy Ant after Tom Rasberry, the pest control operator who discovered it in Texas. Subsequently, a molecular genetic analysis by Zhao et al. (2012) clearly suggested that the ants known as Raspberry Crazy Ants from Texas and Caribbean Crazy Ants from Florida belong to the same species. A broader taxonomic investigation by Gotzek et al. (2012) concurred with this finding. Importantly, however, Gotzek et al. also concluded that these Florida and Texas ants are in fact N. fulva, not N. pubens (and that previous Florida records of N. pubens, a species which now appears to be still limited to the Caribbean, may in fact have been N. fulva as well--and that N. fulva may have been the culprit in earlier historical ant outbeaks in the Caribbean attributed to N. pubens).

Invasive N. fulva are challenging pests. They often occur in tremendous numbers and display supercolony characteristics in which individual colonies do not exhibit mutual aggression toward one another. Individual colonies have multiple females, with nests typically found in a variety of outdoor habitats in rotting wood, in soil, in and under various types of debris, under bark, in potted plants, in vehicles, and in structures. In Texas, they are less active during cooler months, but populations grow rapidly in the spring and increase in size throughout the summer and fall. They are omnivorous, but appear to prefer sweet liquids especially, such as those produced by various hemipterous insects (aphids, mealybugs, scale insects, etc.) and nectaries of plants. They supplement their diets with arthropods and small vertebrates for protein.

The high densities of foraging workers in affected areas make day-to-day activities uncomfortable for humans. These ants do not sting, but are capable of biting. They have been found to displace both native and introduced ants, presumably producing cascading ecological effects as well. They also may cause wildlife to move out of infested areas. The direct economic impact of these ants can be substantial. Failures of electrical equipment have been attributed to large numbers of these ants, which short out circuits and clog switching mechanisms. In some cases, the ants have caused thousands of dollars in damage and repair costs. The range expands at an estimated rate of around 30 m per month in urban areas  and around 207 m/yr in rural areas. In Colombia, N. fulva is considered a serious pest that has reportedly displaced native fauna and caused grassland habitats to dry out as a result of elevated hemipteran levels on plants. Beekeepers in Texas have reported that honey bee hives have been destroyed by this ant species, with the ants reportedly more interested in the bee larvae than in the honey. After killing or driving the bees away, the ants then used the hives for their own colonies.

(Meyers 2008MacGown and Layton 2010 and references therein; Gotzek et al. 2012 and references therein)

Valles et al. (2012) initiated a genomic analysis to identify apparent virus equences from these invasive ants in Florida in the hope of identifying viruses that could be useful in controlling their populations.

More information on the Rasberry Crazy Ant is available from the TAMU Center for Urban and Structural Entomology.

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