Solenopsis invicta, a fire ant originally from the grasslands of South America, has become an important exotic pest in the USA, East Asia, and elsewhere. This species arrived by ship in Mobile, Alabama in the 1930s and has since spread across much of the southern USA. Beginning in 1981, S. invicta has been reported from a growing number of West Indian islands, including Puerto Rico (1981), the Virgin Islands (1988), the Bahamas (1993), Antigua (2000), Caicos Islands (2001), Anguilla (2006), St Martin (2006), Barbuda (2007), Montserrat (2007), Nevis (2007), St Kitts (2007), Aruba (2007), and Jamaica (2010). In the present study, we examined the status of S. invicta on the island of Trinidad.
Although the first published record of S. invicta in Trinidad dates to 2000, we have reliable records of this species from sugarcane and rice growing areas of west-central Trinidad dating to 1991 and specimens collected in 1993. In 2003–2004, we surveyed ants at sites all over Trinidad to document the distribution of S. invicta and its congener, Solenopsis geminata. We collected S. invicta at 60 sites, all in west-central Trinidad. In contrast, we collected Solenopsis geminata at 158 sites spread across all 7 counties of Trinidad. The highest densities S. invicta populations occurred in County Caroni, with scattered populations extending into disturbed areas of County St. George to the north and east, and County Victoria to the south. As of 2004, S. invicta occupied ∼10% of the island, but we see no reason why this species will not spread throughout most open, disturbed sites in Trinidad, displacing S. geminata as the dominant fire ant on the island.
Solenopsis invicta, a fire ant originally from the grasslands of South America, has become an important exotic pest in the US, East Asia, and elsewhere (Ascunce et al. 2011; Wetterer 2013). Solenopsis invicta is well known for its powerful sting, which in humans causes a burning sensation, usually followed within one or two days by the appearance of a white pustule. The venom is hemolytic and neurotoxic and can cause severe allergic responses. Stings can result in secondary infections, sepsis, anaphylactic shock, and even death (Prahlow & Barnard 1998; de Shazo et al. 2004). Solenopsis invicta also poses a significant threat to wildlife (Allen et al. 2004). For example, S. invicta attacks and kills hatchling sea turtles in Florida (Allen et al. 2001; Parris et al. 2002; Krahe 2005).
Solenopsis invicta arrived in North America by ship to Mobile, Alabama in the 1930s. It has spread across the southern US, particularly in open, disturbed areas, causing ecological and economic damage (Buren et al. 1974; Apperson & Adams 1983; Callcott & Collins 1996). The earliest known records of S. invicta in the West Indies are from Puerto Rico (1981) and the Virgin Islands (1988), where S. invicta is now widespread (Buren 1982; Davis et al. 2001; Wetterer & Snelling 2006). More recently, S. invicta has been reported from other islands in the West Indies, including the Bahamas (1993), Trinidad (2000), Antigua (2000), the Caicos Islands (2001), Anguilla (2006), St Martin (2006), Barbuda (2007), Montserrat (2007), Nevis (2007), St Kitts (2007), Aruba (2007), and Jamaica (2010) (Davis et al. 2001; Wetterer & Snelling 2006; Wetterer & Davis 2010; Wetterer 2013).
Davis et al. (2001) reported the only published site record of S. invicta from Trinidad: Caroni Bird Sanctuary in northern County Caroni (labeled “D” in Fig. 1). In the present study, we report earlier unpublished records of S. invicta from Trinidad, and we collected ants from sites throughout Trinidad to delimit the spread of S. invicta.
Materials and Methods
GLW has spent much time working in the field in Trinidad and was stung by a wide variety of ants, but prior to 1991, he did not encounter S. invicta. Beginning in 1991, GLW recorded S. inuicta in sugarcane and rice growing areas of westcentral Trinidad.
In 2003–2004, JKW surveyed ants at sites throughout Trinidad using several different methods. At most sites, JKW conducted visual surveys, collecting all ants encountered until finding at least 6 fire ant specimens OS. invicta and/or S. geminata). To maximize chances of detecting S. invicta, JKW sampled extensively in preferred habitat of S. invicta, i.e., open weedy areas, urban areas, and sugarcane fields. At a subset of sites, JKW conducted much more extensive ant collections, through visual collecting and sifting soil and leaf litter. JKW started sampling for fire ants at Caroni Bird Sanctuary, where Davis et al. (2001) had found S. invicta. Working outward from there, at roughly 1 km intervals, JKW found that the area infested with S. invicta was too extensive to continue this level of sampling. Instead, sampling sites were typically spaced 3–6 km apart in areas surrounding all sites where S. invicta was found. In other parts of the island, distant from any sites with S. invicta, JKW sampled at larger intervals, typically 6–12 km. At many sites, JKW interviewed local people in areas infested with S. invicta to try to gauge its social impact. JKW did not sample in several regions not accessible by paved road, e.g., the interior of the Caroni Swamp and the Nariva Swamp, some mountainous areas, and restricted military and industrial sites.
LRD identified all Solenopsis specimens in this study. We have deposited voucher specimens at Harvard University's Museum of Comparative Zoology and at Florida Atlantic University.
Beginning in 1991, GLW found S. invicta in several locales (labeled “W” in Fig. 1), including La Gloria, Waterloo, Todd's Road, and the Caroni Rice Project, but the earliest specimens were apparently destroyed when air-conditioning failed in the entomology collection at the University of the West Indies. GLW and C. Starr collected the earliest extant S. invicta specimens from Trinidad in Carapichaima on 2 Nov 1993.
JKW collected S. invicta from 60 sites, centering on County Caroni in west-central Trinidad, with a range extending ∼40 km from north to south and ∼20 km from west to east (Fig. 1). In the northwest, the range of S. invicta extended into Port of Spain and its suburbs in County St. George. We found S. invicta as far south as Duncan in County Victoria and as far east as the Santa Rosa racetrack in Arima, County St. George. We found S. invicta in particularly high densities in northern County Caroni. JKW recorded Solenopsis geminata from 158 sites across all seven counties of Trinidad (Fig. 2).
Everyone we spoke with in areas heavily infested with S. invicta knew the white pustules diagnostic of S. invicta stings. Many people (e.g., boat tenders at Caroni Bird Sanctuary) showed off scars on their bare feet and ankles from repeated stings and pointed out large colonies of S. invicta, which they studiously avoided.
In 2003–2004, we found S. invicta restricted to an area in west-central Trinidad occupying about 10% of the island, including most of County Caroni and parts of County St. George to the north and east, and County Victoria to the south (Fig. 1). This area includes much of the traditional “sugar belt” of Trinidad (Pemberton 1990). We see no reason why S. invicta will not invade most open, disturbed sites throughout Trinidad, displacing S. geminata as the dominant fire ant on the island. The present study can serve as a baseline for documenting the spread of S. invicta in Trinidad.
Whereas S. invicta is widespread in Puerto Rico, the Virgin Islands, and the northern Lesser Antilles (see Davis et al. 2001; Wetterer & Snelling 2006; Wetterer & Davis 2010; Wetterer 2013), this species has not yet been recorded from any of the intervening islands north of Trinidad, i.e., Guadeloupe, Marie Galante, Dominica, Martinique, St. Lucia, St. Vincent, Grenada, and Barbados, and Tobago. Nor has S. invicta been recorded from Venezuela immediately to the south and west of Trinidad. It is probably only a matter of time before these areas are also invaded.
Although S. invicta is originally from the grasslands of South America, we suspect that they came to Trinidad from the southeastern US, as appears to be true for other exotic populations in California, Asia, and Australia (Ascunce et al. 2011). It would be useful to use genetic information from S. invicta specimens to evaluate the origin of this infestation in Trinidad and other populations in the West Indies. Future surveys of ants and other invertebrates in neighboring areas with and without S. invicta will allow an evaluation of the ant's ecological impact.
We thank M. Wetterer for comments on this manuscript; C. Starr for his hospitality in Trinidad; W. O'Brien for GIS help; the Fulbright Foundation, the National Science Foundation (DES-0515648), and Florida Atlantic University for financial support.