Tapinoma litorale Wheeler (Hymenoptera: Formicidae) is a small, inconspicuous New World ant that nests in plant cavities, particularly in epiphytes and hollow grass stems and twigs. Recently, T. litorale was included on a list of exotic ant species established in North America, introduced through human commerce. We compiled and mapped >240 site records for T. litorale, documenting the earliest known records for 19 geographic areas, including many with no previously published records: Belize, Colombia, Costa Rica, Guatemala, Haiti, Honduras, Jamaica, San Andrés Island, Trinidad, the Turks & Caicos Islands, and Venezuela. Records for T. litorale ranged from 8.5°N to 29.1°N, spread broadly around the circum-Caribbean region: peninsular Florida, the West Indies, Mexico, Central America, and northern South America. The earliest records of T. litorale come from Florida, the Bahamas, Puerto Rico, and Cuba, and there is no notable distributional gap between Florida and the West Indies. This pattern does not support the proposition that T. litorale populations in North America are exotic. Tapinoma litorale workers resemble ghost ants, Tapinoma melanocephalum (F.), an Old World tramp species that has been spread around the world through human commerce. Tapinoma melanocephalum also nests in plant cavities and potentially may compete with T. litorale in areas where it invades.
Tapinoma litorale Wheeler (Hymenoptera: Formicidae: Dolichoderinae) (sometimes misspelled as littorale) is a small, inconspicuous New World ant that commonly nests in plant cavities, particularly in epiphytes and hollow grass stems and twigs. For example, in the Florida Keys, T. litorale colonies are common in dead saw grass stems (Cladium jamaicense Crantz; Cyperaceae) and red mangrove twigs (Rhizophora mangle L.; Rhizophoraceae) (Simberloff & Wilson 1969; Cole 1982). Recently, Wittenborn & Jeschke (2011) included T. litorale on their list of 93 exotic ant species established in North America, i.e., introduced through human commerce.
Here, we examine the geographic distribution of T. litorale site records and consider evidence of whether or not T. litorale may be exotic to parts of North America. When evaluating the native and exotic ranges of a species, researchers consider a spectrum of distributional, historical, evolutionary, ecological, and genetic information (see Wetterer 2008). For example, evidence considered indicative of a species' native range includes older records largely confined to a single continuous region and occurrence in intact native communities. In contrast, evidence indicative of a species' exotic range includes sudden appearance and spread of the species through an area discontinuous with other known populations, and occurrence exclusively in highly disturbed environments.
Wheeler (1905) described T. litorale from Florida and the Bahamas nesting in epiphytes, hollow grass stems, and twigs of trees and bushes. Putative junior synonyms of T. litorale include Tapinoma litorale cubaense Wheeler, Tapinoma panamense Wheeler, and Tapinoma canalis Wheeler (Longino 2006). Wheeler (1913) described T. litorale cubaense from Cuba, nesting in hollow twigs and epiphytes. Wheeler (1934) described T. panamense from Barro Colorado Island, Panama. Wheeler (1942) subsequently described Tapinoma canalis from Barro Colorado Island, Panama. Shattuck (1992), however, determined that Wheeler's (1942) description was based on the same specimens as T. panamense, and designated T. canalis a junior synonym. Although Bolton (2015) recognized T. panamense as a separate species, Longino (2006) wrote: “I take a broad view of litorale, to include panamense Wheeler 1934 (and its synonym canalis Wheeler 1942). There is considerable variation and there could well be multiple cryptic species.” R. J. G. (unpublished data) made a detailed taxonomic analysis of T. litorale confirming the synonomy of T. litorale cubaense, T. panamense, and T. canalis.
Tapinoma litorale workers are small (~1.5 mm) and monomorphic, and resemble ghost ants, Tapinoma melanocephalum (F.), in size, general appearance, and behavior. The 2 species, however, differ in coloration: T. litorale workers are uniformly yellow or tan, whereas T. melanocephalum workers have a dark brown head and thorax and light tan abdomen.
Materials and Methods
Using published and unpublished records, we documented the range of T. litorale. We obtained unpublished site records from museum specimens in the collections of the Museum of Comparative Zoology (Cambridge, Massachusetts), the Smithsonian Institution (Washington, District of Columbia), Universidad de Guadalajara (Mexico), Instituto Alexander von Humboldt (Colombia), Museo del Instituto de Zoología Agrícola (Venezuela), and Universidad de São Paulo (Brazil). We also obtained specimens from the personal collections of Phil S. Ward (Davis, California), William P. Mackay (El Paso, USA), and John T. Longino (Salt Lake City, Utah). In addition, we used online databases with collection information on specimens by AntWeb ( www.antweb.org). We obtained geographic coordinates for collection sites from published references, specimen labels, maps, or geography web sites (e.g., earth.google.com and www.tageo.com). In addition, J. K. W. surveyed dead twigs and branches of red mangroves and hollow grass stems at sites in peninsular Florida and around the Caribbean region.
In total, we compiled and mapped >240 T. litorale site records (Fig. 1), documenting the earliest known records for 19 geographic areas, including many with no previously published records: Belize, Colombia, Costa Rica, Guatemala, Haiti, Honduras, Jamaica, San Andrés Island, Trinidad, the Turks & Caicos Islands, and Venezuela (Table 1).
J. K. W. recorded T. litorale at 108 sites: in the Bahamas (12 sites); Cozumel, Mexico (2 sites); Florida (69 sites); Roatán, Honduras (2 sites); San Andrés Island, Colombia (1 site); and the Turks and Caicos Islands (22 sites). Tapinoma litorale was the third most common ant that J. K. W found nesting in red mangrove in peninsular Florida, after Xenomyrmex floridanus Emery and Monomorium floricola (Jerdon) (Hymenoptera: Formicidae). We found earlier published and unpublished records of T. litorale from 13 counties in Florida, namely, Brevard, Broward, Charlotte, Collier, Highlands, Indian River, Lee, Martin, Miami-Dade, Monroe, Palm Beach, Pinellas, and Sarasota counties, and collected the first records of T. litorale from St. Lucie and Volusia counties.
Records of T. litorale ranged in latitude from Corcovado National Park, Costa Rica (8.5°N; 1982; J. T. Longino; AntWeb JTLC000009192) in the south, to Daniels Port Orange, Volusia County, Florida (29.1°N; 2015; J. K. W.) in the north.
The color of T. litorale workers varied among different sites. Workers we examined from most sites were pale yellow in color, but tan in some Central American and Greater Antillean populations. R. J. G. (unpublished data) found no consistent morphological differences associated with this color difference.
Earliest known records for Tapinoma litorale from Florida and the West Indies.
We found very few site records for putative junior synonyms T. litorale cubaense, T. panamense, and T. canalis. Some records from Cuba listed T. litorale cubaense (Wheeler 1913; Mann 1920; Reyes 2005), whereas others listed T. litorale (Fontenla Rizo 1993; Fontanela 1999; Portuondo & Fernández 2004). The only published site record for T. panamense and T. canalis is their type locale: Barro Colorado Island, Panama (9.2°N; Wheeler 1934, 1942; Shattuck 1992). In addition, we found 1 specimen record listed as T. panamense on AntWeb (CASENT0280678) from Corcovado National Park, Costa Rica, with the same collection information as other specimens identified as T. litorale.
Tapinoma litorale is widespread in the circum-Caribbean region with records from peninsular Florida, the Bahamas, the Turks and Caicos Islands, the Greater and Lesser Antilles, Mexico, Central America, and northern South America. The earliest records of T. litorale come from Florida, the Bahamas, Puerto Rico, and Cuba, and there is no notable distributional gap between Florida and the West Indies. This pattern does not support the proposition that T. litorale populations in North America are exotic. In fact, we know of no reference other than Wittenborn & Jeschke (2011) that considers T. litorale to have exotic populations in North America.
Except 1 site record from Panama, the earliest record we found of T. litorale from Mexico, Central America, or South America was from 1976 (see Results and Table 2). Although it is possible that T. litorale is a recent arrival in Mexico, Central America, and South America, the fact that most records of T. litorale from this region come from intact natural areas suggests that T. litorale is native there as well. Researchers may easily overlook T. litorale, even in habitats where they are common. For example, when we collected ants from red mangrove twigs, T. litorale workers usually remained packed tightly inside the twigs until we sliced their nest twig open. Thus, simple vegetation beating may often miss T. litorale. When removed from the twig, T. litorale workers move with short bursts of frenetic activity, but then usually freeze, making the ants difficult to capture when they are moving and difficult to see when they freeze.
Earliest known records for Tapinoma litorale from Mexico, Central America, and South America.
We found no reports of T. litorale as a pest. Tapinoma litorale workers resemble those of T. melanocephalum, an Old World tramp species that has been spread around the world through human commerce and is a common household pest (Wetterer 2009). Tapinoma melanocephalum also nests in plant cavities, including hollow grass stems and red mangrove twigs, and in areas where it invades, it could compete with T. litorale and other native species.
We thank M. Wetterer for comments on this manuscript; A. Schaffner, A. Inamoto, A. Ardelean, A. Ridgeway, B. Liddell, C. Danley, C. Olbrych, D. Arrieta, D. Brothers, G. Kramer, J. Herr, K. Kelly, L. Feliciano, M. Merritt, S. Crary, S. Groth, T. Holmes, and T. Bertolami for field assistance; Fernando Fernández (MHN-ICN), J. T. Longino (JTLC), M. Vásquez (CZUG), S. Cover (MCZ), P. S. Ward (UC at Davis), T. Schultz (SI), and W. P. Mackay (UT at El Paso) for help with their respective ant collections; D. P. Wojcik and S. D. Porter for compiling their valuable FORMIS bibliography; L. Lesperance of the FAU library for processing so many interlibrary loans; Florida Atlantic University for financial support. R. J. G. was partially supported with funds from The Ernst Mayr in Animal Systematics Travel Grants, and the research project “Systematics and Evolution of the Ant Genus Tapinoma Föerster (Formicidae: Dolichoderinae) in the Neotropical Region” supported by Colciencias-Universidad del Magdalena through agreement #008-2015.