Nylanderia fulva, full face view of a worker from TX (click image to enlarge).

Nylanderia fulva, full face view of a worker from MS (click image to enlarge).

Introduction
Ants in the genus Nylanderia (Formicinae) are relatively small, pale yellow to almost black, and can be distinguished from other Formicinae in our region by the coarse, long, dark setae (macrochaetae), which are arranged in distinct pairs on the dorsum of the head and alitrunk.

Update on the identity of the crazy ant in the southeastern US

A new study by Gotzek et al. (2012) has shown that the crazy ant that has been plaguing the southeastern US is Nylanderia fulva (not N. pubens). The researchers used both DNA and morphometric techniques for this study. This paper is online at: http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045314

Nylanderia fulva is an exotic species thought to be native to South America. This name of this species has been a constant source of confusion since large populations started showing up in Florida in the 1990's (Klotz et al. 1995). Florida specimens were identified as N. pubens based on earlier records of N. pubens reported from Florida 60+ years earlier (Trager, 1984). It is likely that N. pubens was present in Florida historically, but that subsequently N. fulva was introduced and became the dominant species. If so, this would explain why N. pubens has not been commonly found in Florida in recent years. In the US, Nylanderia pubens is likely restricted to southern FL. When this ant was first discovered in Texas in 2002 (Meyer, 2008), researchers were hesitant to identify it as N. pubens or N. fulva, because of some minor differences in size. Until the identity could be confirmed, specimens from Texas were called Nylanderia species near pubens. Then, in 2009 it was detected along the coast of Mississippi (MacGown and Layton, 2010), and in 2010 it was reported from Louisiana (Hooper-Bui et al. 2010). Specimens from MS and LA have been referred to as N. species near pubens, N. pubens, and N. species near fulva.

Researchers at Texas A&M University did morphometric and DNA studies to help determine its identity, but results were inconclusive. In Trager's revision of Nylanderia for the continental United States (Trager, 1984), he mentioned a record of N. pubens from Brownsville, TX, but remarked that is was incorrectly identified and was really N. fulva, a South American species. These two species are both in the same group (N. fulva group) and are similar enough that Creighton (1950) synonymized them. Likewise, as recently as 2007, N. pubens was considered a synonym of N. fulva (Bolton et al. 2007). In Trager's revision (1984), he noted that the paramere of the male genitalia of N. pubens was bordered by a dense fringe of at least 30 blondish macrochaetae (see photo above); whereas, he stated that the paramere of N. fulva had "sparse pilosity of uneven length and orientation (see photo above) which in no way resembles the characteristic fringe of N. pubens." Interestingly, all male specimens I have examined from TX, LA, MS, and FL have paramere macrochaetae matching Trager's description of N. fulva, rather than N. pubens, which means, if Trager was correct in his concept of these two species, then the species currently causing problems from FL to TX is N. fulva. Other evidence pointed to the conclusion that specimens found throughout the southern US are all the same species. In a recent study using molecular techniques by Zhao et al. (2012), specimens from TX and FL were found to be a single species.

Complicating things further was the fact that N. fulva has eight subspecies, some of which may or may not really be valid. A revision of the genus in the Nearctic region is currently being done by Bob Kallal, a student of John LaPolla at Towson University, and hopefully these questions will be answered. So basically, since this this species has been reported in the US, it has not been certain whether the name should be N. fulva or N. pubens. Based on its its obvious similarity to Florida specimens, where it was first reported in the US, I previously used the name N. pubens so as to be "on the same page" as others in the region until such time as the group was revised. But, more recently I have followed Trager's concept of the species and refer to the species as N. fulva. This name has proven to be correct in the recent study by Gotzek et al. (2012) that has finally identified our southeastern species as N. fulva.

The common name of N. fulva is the hairy crazy ant, although it has also been called the Caribbean crazy ant in Florida and the Caribbean region and in TX it has been called the "Rasberry crazy ant", named after Tom Rasberry, the pest control operator who first discovered them in that state. Efforts are now underway to adopt a new common name for this species to avoid confusion with N. pubens. So far the name that has the most support is the "tawny crazy ant".

Identification
Worker: Color reddish-brown; size fairly large overall length approximately 2.0-2.5 mm, HL 0.77-0.85 mm; eye size average for genus (OI 23-26); ocelli lacking; macrochaetae long, somewhat flexuous; head in frontal view with relatively dense pubescence, side of pronotum with dense pubescence; acidopore present at tip of gaster.

Female: Similar coloration to workers; about 4.0 mm in overall length; acidopore present at tip of gaster.

Male: Similar coloration to workers; size slightly larger than workers, about 2.4-2.7 mm in overall length; eye size much larger; with well developed wings; genitalia external with well developed parameres; parameres with sparse pilosity of uneven length and orientation.

In the US, Nylanderia fulva is most similar to N. pubens, of which the workers cannot be reliably separated using morphological techniques at this time. On average, workers of N. fulva are smaller (TL 2.00-2.5 mm) as compared to N. pubens (TL 2.75-3.0 mm); the posterior border of head is straight or only weakly emarginate (emarginate in N. pubens); and the head has much denser pubescence (sparser in N. pubens). However, males of N. fulva can be easily distinguished from N. pubens by the less regular rows of setae along the borders of the parameres of the male genitalia (see photo above). In N. pubens, the setae on the parameres are arranged in a definite fan-like pattern (see photos above). In the field, hairy crazy ants superficially resemble Argentine ants, Linepithema humile (Mayr), but can be differentiated by their slightly larger size, reddish color, and erratic foraging patterns. Argentine ants are dark brown in color, slightly smaller, and do not move as fast or as erratically.  Under the microscope, they are easily distinguished from Argentine ants by their reddish-brown coloration, the presence of an acidopore at the tip of the gaster, and numerous erect, thickened, elongate setae on the body and antennal scapes. The elongate crazy ant (Paratrechina longicornis) also has large populations and behaves similarly.  Elongate crazy ants are brown, more slender, and have extremely long legs and antennae. Other species of Nylanderia in the southern United States having dense pubescence on the alitrunk are N. bourbonica (Forel) and N. guatemalensis (Forel). Workers of Nylanderia bourbonica are larger, concolorous dark brown, and have ocelli; whereas, workers of N. guatemalensis are yellowish-brown and have a glabrous pronotal disk, with the sides of pronotum usually glabrous as well.

Biology and Economic Importance
In the U.S., this ant has become a serious nuisance species that has incredibly large populations and has proven difficult to control with conventional baits (Warner and Scheffrahn, 2004). Since its initial detection in Texas in 2002, it has caused serious economic and ecological damage in southern Texas (Meyer, 2008b).

Because this ant was only recently detected in Mississippi, its impact there is yet to be determined. On a visit to an infested site in Hancock County in the fall of 2009 by Dr. Blake Layton (MSU extension entomologist) and I, we were amazed by the incredible numbers of ants present at the site (which was roughly a square mile). The homeowners had tried repeated applications of various pesticides with no visible results. In addition to the obvious nuisance quality they presented, the ants also caused physical damage to a camper in which their colonies had forced the outer metal wall to bulge outward, to insulation of which the ants chewed through leaving powder behind, and some electrical boxes, which were shorted out. The winter of 2009-2010 proved to be quite cold on the Mississippi coast and several sub-freezing nights negatively impacted plants (such as palms). We were curious if the cold weather also affected the crazy ant populations, so Dr. Layton and I made a return trip to the site in March of 2010. The ants were not as obvious and abundant as during our previous trip, which was heartening. However, we found colonies of the ants under bark of pine stumps and in rotting pine logs, where they had apparently overwintered. High abundance of this species was again observed at this locality during a trip back to the area in June, 2011. In addition to the populations in Hancock County, we found this species at multiple localities in southern Jackson County in late 2010. We made a visit to that area in June 2011 and found abundance to be at a high levels.

Individual colonies and groups of colonies are polygynous, with nests typically found in rotting wood, in soil, in and under various types of debris and landscape objects, under mulch, under bark, in potted plants, in vehicles, and in structures. Colonies are less active during cool months; however, populations build rapidly in the spring and increase in size throughout the summer and fall. Hairy crazy ant workers tend various sucking hemipterous insects (aphids, mealybugs, scale insects, treehoppers, whiteflies, etc.) for honeydew (a sugary liquid extracted from plant hosts), which is excreted from the plant hosts. They are also attracted to plant nectaries, damaged or overripe fruit, and other sweet food sources. They supplement their diets with arthropods and small vertebrates for protein (Drees 2009, Gold 2011, MacGown 2011, Meyers 2008).  We have observed this species tending Membracidae in Hancock County, MS (see photo above).

At this time, the economic and ecological impacts of this species are not fully known. In general, the hairy crazy ant is a serious nuisance pest. High densities of foraging workers in affected areas make day-to-day activities uncomfortable, if not impractical. This species does not sting, but is capable of inflicting a bite and spraying small quantities of formic acid, which may irritate some individuals.  Hairy crazy ants may reduce biodiversity of other animals, both invertebrate and vertebrate. Gold (2011) reported that tree-nesting birds and other small animals have been forced to move out of areas inhabited by large populations of crazy ants. Wetterer and Keularts (2008) reported that large numbers of N. pubens workers caused deaths of caged rabbits in St. Croix. In Colombia, N. fulva is considered a serious pest that has displaced native fauna; caused chickens to die of asphyxia; attacked larger animals, such as cattle, around the eyes, nasal fossae and hooves; and caused grassland habitats to dry out as a result of elevated hemipteran levels on plants (Arcila et al. 2002, Meyers 2009). Another exotic ant species, Pheidole obscurithorax Naves, from South America, which has much lower population levels than the hairy crazy ant, has been documented to attack hatchling chickens in Mississippi (Hill 2006). Large levels of the hairy crazy ant could be detrimental to the poultry industry in Mississippi if left unchecked.  At high densities, this species shows potential to be an important agricultural pest due to its enhancement of phloem-feeding hemipterous insects that it tends (Wetterer and Keularts 2008). This species has been blamed for crop damages due to high numbers of plant feeding Hemiptera in St. Croix (Pagad 2011).  Effects on tree health from increased levels of sap-feeding hemipterans tended by ants remains largely unstudied in this species.  High densities of scale insects tended by the related yellow crazy ant, Anoplolepis gracilipes (Smith), have been reported to weaken trees and cause canopy dieback and/or death of trees from a sooty mould in the honeydew produced by the scale insects (Matthews 2004).  Hairy crazy ants have been reported to destroy honey bee hives in Texas by consuming brood, and then colonizing the hive (Drees, 2009, Harmon 2009). Their presence in various materials being transported (i.e. hay, mulch, potted plants, etc.) may reduce value of goods (Drees 2009). Large accumulations of hairy crazy ants have been reported causing short circuits and clogging switching mechanisms, which has resulted in electrical shortages in a variety of equipment such as phone lines, air conditioning units, chemical-pipe valves, computers, security systems, and sewage lift pump stations (Drees 2009, Pagad 2011, Meyers 2008b). Due to large populations, this species is difficult to control, and typically requires professional exterminators. 

Distribution

Worldwide (non US sites) 

Anguilla, Argentina, Bermuda, Brazil, Colombia, Cuba, Guadeloupe, Martinique, Mexico, Panama, Puerto Rico, St. Croix, St. Vincent & the Grenadines (Lesser Antilles), Virgin Islands (USA),  (MacGown 2011, Trager 1984, Pagad 2011, Wetterer and Keularts 2008).

United States

Florida:  Alachua, Bay, Brevard, Broward, Clay, Collier, DeSoto, Duval, Hardee, Hillsborough, Indian River, Lee, Manatee, Marion, Martin, Miami-Dade, Orange, Palm Beach, Pasco, Pinellas, Polk, Saint Johns, Saint Lucie, and Sarasota Counties (Calibeo and Oi 2011, Deyrup et al., 2000; Klotz et al., 1995, Warner and Scheffrahn 2010, Pers. Comm. Dawn Calibeo-University of Florida).

Mississippi:  Hancock, Harrison, and Jackson Counties (MacGown 2011 and MEM records).

Louisiana:  Calcasieu and West Baton Rouge Parishes, (Hooper-Bui et al. 2010, Morgan 2011).

Texas:  Bexar, Brazoria, Brazos, Cameron, Comal, Fort Bend, Chambers, Galveston, Hardin, Harris, Hidalgo, Jefferson, Jim Hogg, Liberty, Matagorda, Montgomery, Nueces, Orange, Polk, Travis, Victoria, Walker, Wharton, and Williamson Counties (Gold 2011, Meyers 2008a,b, Meyers 2009).

Videos

A video of hairy crazy ants from Hancock County, MS, taken in the fall of 2009.

A short video of hairy crazy ants that shows their frenetic nature.

Literature Cited

Arcila, A.M., L.A. Gómez, and P. Ulloa-Chacón. 2002. Immature development and colony growth of crazy ant Paratrechina fulva under laboratory conditions (Hymenoptera: Formicidae). Sociobiology 39: 307-321.

Bolton. B, G. Alpert, P. S. Ward, P. Naskrecki. 2007. [CD-ROM] Bolton's Catalogue of the Ants of the World.  Harvard University Press.

Calibeo, D. and F. Oi. 2011. Caribbean crazy ants: A new pest in the Southeast [pp. 11-12]. In: Harmon, C. L., S. D. Stocks, and A. Hodges.  First Detector Network News. 6 (9):  1-12.

Creighton, W. S. 1950.  The Ants of North America. Bulletin: Museum of Comparative Zoology 104:  1-585. 

Deyrup M, Davis L., Cover S. 2000. Exotic ants of Florida. Transactions of the American Entomological Society 126: 293-326.

Drees, B. M. 2009. Rasberry crazy ant – a new threat to nurseries. American Nurseryman. November 2009: 6-8.

Gold, R. 2011. Rasberry Crazy Ant, Nylanderia sp. nr. pubens. Texas A&M University, Center for Urban and Structural Entomology. Available online at: http://urbanentomology.tamu.edu/ants/exotic_tx.cfm (Accessed on 21 September 2011).

Gotzek, D., S.G. Brady, R.J. Kallal, and J.S. LaPolla. 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. (online at: http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045314)

Harmon, K. 2009. Honeybees Face New Threat in Texas: "Crazy" ants. On-line posting (http://www.scientificamerican.com/blog/post.cfm?id=honeybees-face-new-threat-in-texas-2009-08-07), accessed 3 November 2009.

Hill, J. G. 2006. First report of the exotic ant, Pheidole obscurithorax Naves (Hymenoptera: Formicidae), attacking a hatchling chicken. Journal of Entomological Science 41: 397-398.

Hooper-Bui, L. M., R. Strecker, X. Chen, D. Aguillard, and A. Miller. 2010. Super colonies of crazy ants in Louisiana.  Proceedings of the 2010 Imported Fire Ant and Invasive Ant Conference, Little Rock Arkansas, USA, April 19-22, 2010. pp. 13-16.

Klotz J. H, Mangold J. R, Vail K. M, Davis, Jr. L.R, Patterson R. S. 1995. A survey of the urban pest ants (Hymenoptera: Formicidae) of peninsular Florida. Florida Entomologist 78: 109-118.

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.

MacGown, J. A. and B. Layton.  2010. The invasive Rasberry crazy ant, Nylanderia sp. near pubens (Hymenoptera:  Formicidae), reported from Mississippi (available online at: http://midsouthentomologist.org.msstate.edu/Volume3/Vol3_1_html_files/vol3_1_008.htm).  Midsouth Entomologist Vol 3: 1:  441-47. [pdf]

Matthews, S. 2004.  The Global Invasive Species Programme: Tropical Asia invaded, the growing danger of invasive species.  64 pp. [pdf]

Meyers, J. May 2008a. Exotic Texas Ant, Nylanderia sp. nr. pubens. Center for Urban & Structural Entomology, Texas A&M University. http://urbanentomology.tamu.edu/ants/exotic_tx.cfm (accessed 16 May 2008).

Meyers, J. M. 2008b. Identification, Distribution and Control of an Invasive Pest Ant, Nylanderia sp. (Hymenoptera: Formicidae), in Texas. Ph.D. dissertation, Texas A & M, University. 163 pp. [pdf]

Meyers, J.M. 2009. Exotic Texas Ant, Paratrechina sp. near pubens. Texas A&M University Fact Sheet. 1-4 pp.

Morgan, J. W. 2011. Hairy Crazy Ants Make La. Their New Home.  LSU AgCenter.com Headline News. Available online at: http://www.lsuagcenter.com/en/communications/news/headline_news/Hairy-crazy-ants-make-La-their-new-home.htm (Accessed on. 22 Sept. 2011).

Pagad, S. 2011. Global Invasive Species Database: Nylanderia (=Paratrechina) pubens (insect). Available online at: http://issg.org/database/species/ecology.asp?si=1553&fr=1&sts=&lang=EN.  (Accessed on 28 Sept. 2011)

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

Warner, J. and R. H. Scheffrahn. 2004. Featured Creatures: Carribean crazy ant, Nylanderia pubens (Forel) (Hymenoptera: Formicidae: Formicinae). University of Florida Institute of Food and Agricultural Sciences. http://creatures.ifas.ufl.edu/urban/ants/caribbean_crazy_ant.htm (Accessed on 16 May 2008).

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. Fla. Entomol. 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. Accepted for publication. [online summary and abstract available online: http://www.ars.usda.gov/research/publications/publications.htm?seq_no_115=272968].

Links, Factsheets, and papers

AntWeb Images
Discover Life Images

MacGown, J. A. and B. Layton.  2010. The invasive Rasberry crazy ant, Nylanderia sp. near pubens (Hymenoptera:  Formicidae), reported from Mississippi (available online at: http://midsouthentomologist.org.msstate.edu/Volume3/Vol3_1_html_files/vol3_1_008.htm).  Midsouth Entomologist Vol 3: 1:  441-47. [pdf]

Exotic Texas Ant, Nylanderia sp. nr. pubens- http://urbanentomology.tamu.edu/ants/exotic_tx.cfm

Wild, A. 2012. How to identify Nylanderia fulva, the hairy crazy ant. - http://myrmecos.net/2012/06/26/how-to-identify-the-hairy-crazy-ant-nylanderia-fulva/