Tawny crazy ants (TCA), Nylanderia fulva (Mayr), have recently received widespread attention in the regional, national, and even international media since public announcements were disseminated about their presence in Louisiana and Mississippi. The main concern associated with these unwelcome additions to the ant fauna of Louisiana is the fact that they establish large “supercolonies” containing multiple queens distributed among multiple nests and many millions of workers. This results in large, widespread infestations that may be difficult to control using methods focused on eliminating individual colonies, as occur with fire ants. Also, predicting exactly how TCA will impact the human and native fauna of Louisiana is difficult because newly established invasive species bring an element of ecological uncertainty when they occupy new landscapes and habitats.

What’s in a name?

Reporting the movement and first occurrences of the TCA has been confounded by the use of different common and scientific names to refer to a single species. Deyrup et al. (2000) reported the species from south Florida, where it has been established for many years under the scientific name Paratrechina pubens Forel. The species was placed in the genus Paratrechina for many years. These and other authors referred to it under the common name “hairy crazy ant,” which is what the specific epithet “pubens” translates to in English. But the name “Caribbean crazy ant” also appears in the literature, after the presumed origin of the species in the Caribbean region. The species was transferred to the genus Nylanderia by LaPolla et al. (2010). When the species was first reported in Texas during 2002, it was believed to represent an undescribed species and was referred to under the technical, though not taxonomically valid name, Nylanderia nr. pubens, meaning “near” N. pubens, but a different species. The common name “Rasberry crazy ant” was used, after Houston pest control operator Tom Rasberry (Meyers and Gold 2008). MacGown and Layton (2010) reported the species from Hancock Co., Mississippi, and referred to it as the “hairy crazy ant.” Aguillard et al. (2011) reported a population of supercolony-forming crazy ants from West Baton Rouge Parish, Louisiana, but referred to them as Nylanderia nr. fulva. These West Baton Rouge Parish specimens are vouchered in the City of New Orleans Mosquito and Termite Control Board Teaching Collection (pers. comm., Kenneth Brown, BASF Pest Control Solutions). Nylanderia pubens was originally described as a subspecies of N. fulva, but was elevated to species rank by Trager (1984), and the two species are quite similar, with indistinguishable workers and similar habits (Aguillard et al. 2011). Meyers (2008) addressed the question of whether the Texas populations referred to as N. nr. pubens were distinct from the Florida and Caribbean populations of N. pubens. Based on morphological and molecular data, he concluded that these are the same species. These results were corroborated by recent molecular comparisons based on multiple genes (Zhao el al. 2012). Additional recent work confirmed that the species in the U.S. Midsouth represents N. fulva (Mayr) based on comparison of types, morphology and molecular data (Gotzek et al. 2012), and those authors referred to the species using the common name "Rasberry crazy ant." The Entomological Society of America's Common Names Committee added to the confusing string of common names during 2013 by proposing yet another common name, the "tawny crazy ant" (Ferro 2013). Male ants are necessary to distinguish the two similar species N. fulva and N. pubens morphologically.

Arrival in Louisiana

Entomologists have been expecting this pest ant to arrive in Louisiana for the past several years from the adjacent counties in Texas and/or Mississippi. Therefore, it was no surprise when ants collected in Calcasieu Parish, Louisiana, were identified by LSAM diagnostician Victoria Bayless during June 2011. These represented the first record of this species in the state based on specimens submitted to the Louisiana State Arthropod Museum. But, as noted above, ants apparently representing this species were also present in West Baton Rouge Parish. Subsequent samples submitted to the LSAM from Ascension, Terrebonne, East Baton Rouge, and Lafayette Parishes have also been identified as TCA. Specimens submitted to the LSAM and identified as TCA are identical in appearance to samples of TCA from Florida provided by Anthony Pranschke (Sarasota County Mosquito Management Services), which included males that allowed positive identifications. Florida and Louisiana specimens are consistent with images of N. fulva males illustrated on the Ants of Mississppi website.

These records and recent anecdotal reports indicate that TCA is well established in south-central Louisiana, and it can probably be expected to spread across much of the remainder of the state, especially the southern one-half. In fact, Gotzek et al. (2012) suggested that the species is already much more widely distributed than currently reported. All reported occurrences involve infestations of multiple dwellings/buildings and yards. These reports are consistent with situations reported from both Texas and Mississippi. Wetterer and Keularts (2008) reported population explosions of hairy crazy ants on St. Croix, U.S. Virgin Islands that caused crop damage and death to small livestock (i.e., rabbits). Wetterer (2007) suggested N. pubens as a potential candidate species for the “plague ants” of Bermuda during the 19^th century, and included a number of vivid and alarming quotes from early written accounts of the infestations. Reports that TCA are capable of displacing red imported fire ants may come as small consolation if infestations in Louisiana achieve levels recorded in these historical archives.

Correct identification of the causal organism is the first step in addressing any entomological problem. If you suspect you may have an infestation of these unwelcome new arrivals, you may submit samples to the Louisiana State Arthropod Museum for identification. Go to the LSAM website (www.lsuinsects.org) for submission instructions.

Summary

The species Paratrechina fulva and P. pubens were transferred to Nylanderia and have been referred to using the common names "hairy crazy ant," "Caribbean crazy ant," and, most recently, "tawny crazy ant." An unidentified "species" was called Nylanderia nr.pubens and referred to using the common names “Rasberry crazy ant” and "hairy crazy ant." Another unidentified "species" was called Nylanderia nr. fulva, implying similarity to Nylanderia fulva. Invasive tawny crazy ants in Louisiana and across the midsouth region have be positively confirmed as N. fulva based on multiple sources of data, including molecular sequences and type specimen analysis. Even with the use of modern search engines, homeowners seeking information about this pest may find it difficult to obtain accurate information about identification and control with so many names in use. Researchers, pest control operators, and homeowners should accurately identify pest species as the first step in developing rational, environmentally responsible pest management solutions.

Additional Online Resources

Excellent photographs of Nylanderia fulva may be found at MacGown’s (2012) Ants of Mississippi website.

For useful information about the species’ status in Texas and management strategies that may apply equally to Louisiana, see Texas A&M’s (2008) crazy ant webpage.

References

Aguillard, D., R. M. Strecker, and L. M. Hooper-Bùi. 2011. Extraction of super colonies of crazy ants from soil and wood. Midsouth Entomologist 4: 53-56.

Ferro, M. L. 2013. Common name selection in the internet age: a crazy case study. American Entomologist 59: in press.

Lapolla, J. S., S. G. Brady, and S. O. Shattuck. 2010. Phylogeny and taxonomy of the Prenolepis genus-group of ants (Hymenoptera: Formicidae). Systematic Entomology 35: 118-131.

Gotzek D, Brady S. G., Kallal R. J. , LaPolla J. S. 2012. The Importance of Using Multiple Approaches for Identifying Emerging Invasive Species: The Case of the Rasberry Crazy Ant in the United States. PLoS ONE 7(9): e45314. doi:10.1371/journal.pone.0045314

MacGown, J. A., and B. Layton. 2010. The invasive Rasberry crazy ant, Nylanderia sp. near pubens (Hymenoptera: Formicidae), reported from Mississippi. Midsouth Entomologist 3: 441-447.

Meyers, J. M. 2008. Identification, distribution, and control of an invasive pest ant, Paratrechina sp. (Hymenoptera: Formicidae) in Texas. Doctoral dissertation. 177 pages. Texas A&M University, Texas.

Meyers, J. M. and R. E. Gold. 2008. Identification of an exotic ant, Paratrechina sp. nr. pubens (Hymenoptera: Formicidae), in Texas. Sociobiology 52: 589-603.

Trager, J. C. 1984. A revision of the genus Nylanderia (Hymenoptera: Formicidae) of the continental United States. Sociobiology 9: 49-162.

Wetterer, J. K. 2007. The vanished plague ants (Hymenoptera: Formicidae) of 19^th century Bermuda. Myrmecologische Nachrichten 8: 219-224.

Wetterer, J. K., and J. L. W. Keularts. 2008. Population explosion of the hairy crazy ant, Paratrechina pubens (Hymenoptera: Formicidae), on St. Croix, US Virgin Islands. Florida Entomologist 91: 423-427.

Zhao, L., J. Chen, W. Jones, and D. Oi. 2012. Molecular comparisons suggest caribbean crazy ant from Florida and Rasberry crazy ant from Texas (Hymenoptera: Formicidae: Nylanderia) are the same species. Environmental Entomology 41: 1008-1018.