JHR 54: 33-4 I (20 I 7) or % JOURNAL OF A peer-reviewed open-access Journal doi: 10.3897/jhr.54.11444 ) Hymenopter a http://jhr.pensoft.net Thelnternaonl Society of Hymenopexriss, RESEARCH Invasive ants of Bermuda revisited James K. Wetterer' | Wilkes Honors College, Florida Atlantic University, 5353 Parkside Drive, Jupiter, FL 33458, USA Corresponding author: James K. Wetterer (wetterer@fau.edu) Academic editor: P Klimes | Received 9 December 2016 | Accepted 23 January 2017 | Published 27 February 2017 http.//zoobank. org/3 CE53 C12-5D4B-42C2-87 1D-8F4239783DB2 Citation: Wetterer JK (2017) Invasive ants of Bermuda revisited. Journal of Hymenoptera Research 54: 33-41. https:// doi.org/10.3897/jhr.54.11444 Abstract For 60+ years, two of the world’s most widespread and destructive invasive ant species, the African big- headed ant (Pheidole megacephala) from tropical Africa and the Argentine ant (Linepithema humile) from subtropical South America, have been engaged in an epic battle on the islands of Bermuda. Both species are completely intolerant of the other and are also well-known for killing off native invertebrates, particu- larly other ants. Here I surveyed sites across Bermuda in 2016, including resurveys of the locations previ- ously surveyed in 1963, 1966, 1973, 1986, and 2002, to provide an update on this conflict. The status of all other ant species present in the islands, including previous records from literature, is also provided. In addition, I surveyed ants nesting in red mangrove (Rhizophora mangle) trees to evaluate whether this arboreal habitat may serve as a refuge for previously overlooked ant species. In 2016, L. humile occurred at most surveyed sites in Bermuda, including all ten resurveyed sites. Pheidole megacephala was present at only two resurveyed sites, a lower proportion of sites than any of the five earlier surveys. Still, P megacephala occupied substantial areas, particularly in and around Hamilton, the capital of Bermuda. This survey increased the number of ant species with verified records from Bermu- da to 25, including four exotic species recorded for the first time: Cardiocondyla minutior, Pheidole navi- gans, Strumigenys emmae, and Strumigenys membranifera. | found five ant species nesting in mangroves: L. humile plus four Old World exotics, C. minutior, Cardiocondyla obscurior, Monomorium floricola, and Plagiolepis alluaudi. It appears that L. humile may be better suited to the subtropical climate of Bermuda than P mega- cephala, except perhaps in warmer and sunnier habitats, such as plantings along urban streets and in open parks, where P megacephala may hold the advantage. The dataset on the new ant records from 2016 is provided with the paper. Keywords Atlantic islands, biodiversity, exotic ants, Pheidole megacephala, Linepithema humile, tramp ants Copyright James K.Wetterer. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 34 James K. Wetterer / Journal of Hymenoptera Research 54: 33-41 (2017) Introduction For more than 60 years, two of the world’s most widespread and destructive invasive ant species, the African big-headed ant (Pheidole megacephala) from tropical Africa and the Argentine ant (Linepithema humile) from subtropical South America, have been engaged in an epic battle on the Atlantic islands of Bermuda. Pheidole megacephala was first recorded in Bermuda in 1889 (Dahl 1892), and was the dominant ant species there in the early 20th century (Haskins 1939, Wetterer and Wetterer 2004). When L. humile arrived in Bermuda in the 1940s, however, this new invader quickly took over much territory, displacing P. megacephala. Still, P. megacephala maintained many strongholds, and ever since, these two species have been contesting ever-shifting bat- tlefronts between mutually exclusive territories that together occupy most of the land area of Bermuda (Haskins 1939; Haskins and Haskins 1965, 1988; Crowell 1968; Lieberburg et al. 1975; Wetterer and Wetterer 2004). Both P. megacephala and L. humile are well-known for killing off native in- vertebrates, particularly ants (Erickson 1971; Human and Gordon 1996; Hol- way 1999; Wetterer et al. 2000, 2001; Wetterer 2002). During their tenure in Bermuda, P. megacephala and L. humile have almost certainly had a devastating impact on native invertebrates. In addition to the two dominant ant species, Wet- terer and Wetterer (2004) reported confirmed records of 18 other ant species from Bermuda. Subsequently, I found museum specimens of two more ant spe- cies from Bermuda: Nylanderia cf. fulva (reported as Paratrechina pubens; Wet- terer 2007) and Monomorium floricola (see Wetterer 2010), bringing the total number of known species to 21 (plus one male specimen identified only to genus; see Results). It is unclear whether any ant species now living in Bermuda are na- tive, i.e., predating human arrival. In the present study, I surveyed sites across Bermuda to provide an update on this conflict and on the status of other ant species present. In addition, I surveyed ants nesting in red mangrove (Rhizophora mangle) to evaluate whether this arboreal habi- tat may serve as a refuge for some previously overlooked ant species. Red mangroves grow in and adjacent to shallow brackish water in subtropical and tropical estuaries around the world, providing a unique habitat, often completely isolated from any terrestrial habitat. Methods In 3-10 May 2016, I surveyed ants in Bermuda. I hand-collected ants using an aspi- rator, sifted litter using a Davis sifter, and collected ants from inside dead twigs and branches of red mangrove. To examine changes in which ant species, P. megacephala or L. humile, dominated specific areas in Bermuda, Haskins and Haskins (1988) re-surveyed ten sites that had been surveyed earlier. Wetterer and Wetterer (2004) surveyed these same ten sites. Invasive ants of Bermuda revisited 35 In 2016, I again surveyed ants at these ten sites using hand collecting and litter sifting (geo-coordinates and collection date in parentheses): Roe e BAe a Great Head Park (32.368, -64.650; 9 May 2016) Mullet Bay Road and Ferry Road intersection (32.375, -64.696; 5 May 2016) Leamington Caves (32.342, -64.708; 4 May 2016) Knapton Hill Road and Harrington Sound Road intersection (32.321, -64.716; 4 May 2016) Knapton Hill Road and Harrington 100s Road intersection (32.315, -64.724; 5 May 2016) Christchurch Lane and Brighton Hill Road intersection (32.306, -64.754; 9 May 2016) Spittal Pond Reserve (32.311, -64.724; 5 May 2016) Newstead Hotel (32.284, -64.787; 9 May 2016) Wreck Road (32.276, -64.881; 8 May 2016) . Ireland Island (32.327, -64.835; 8 May 2016) I collected dead twigs and branches of red mangrove into 3.8-liter zip-lock storage bags (3-10 bags from different mangrove trees, depending on the number of acces- sible trees) at 14 sites in Bermuda (geo-coordinates, collection date, and # of bags in parentheses): ONAN RON | Tom Wood’s Bay (32.304, -64.814; 3 May 2016; 10) Hungary Bay (32.291, -64.760; 3 May 2016; 10) Crow Lane Park (32.293, -64.771; 3 May 2016; 10) Mangrove Lake (32.326, -64.711; 4 May 2016; 10) Trott’s Pond (32.330, -64.702; 4 May 2016; 10) Walsingham Bay (32.346, -64.709; 4 May 2016; 10) Coot Pond (32.389, -64.678; 5 May 2016; 4) Mullet Bay Rd and Ferry Rd (32.375, -64.696; 5 May 2016; 4) Stokes Point Park (32.371, -64.694; 5 May 2016; 3) . Blue Hole (32.351, -64.710; 5 May 2016; 10) . Fairyland Creek (32.295, -64.802; 6 May 2016; 10) . Mill Creek (32.304, -64.801; 7 May 2016; 10) . The Lagoon (32.313, -64.844; 8 May 2016; 10) . Pilchard Bay (32.276, -64.880; 8 May 2016; 10) I also did hand collecting and litter sifting in areas adjacent to each red mangrove sites, as well as at numerous other sites when time and weather permitted. On the last day of collecting (10 May 2016), I surveyed 12 urban sites in and around Hamilton city, the capital of Bermuda. In addition, three people (R. Franco, J. Steele, and C. Stringer) sent me samples of ants they collected in and around their homes in Bermuda in May 2016. I retained all pinned and alcohol specimens in my personal collection. 36 James K. Wetterer / Journal of Hymenoptera Research 54: 33-41 (2017) Results In 2016, I collected a total of 19 ant species in Bermuda, including four recorded for the first time: Cardiocondyla minutior, Pheidole navigans, Strumigenys emmae, and Strumigenys membranifera (Table 1, See Suppl. material 1. These records bring the total number of confirmed ant species records from Bermuda to 25. Bermuda Department of Agriculture has previously intercepted P navigans (recorded as Pheidole moerens) on in-coming goods (Wetterer and Wetterer 2004). Wetterer and Wetterer (2004) re- ported a male dacetine ant (Tribe Dacetini) that could not be identified to species level. It seems likely that this dacetine was one of the two newly reported Strumigenys species. In their 2002 survey, Wetterer and Wetterer (2004) found L. /umile in large num- bers at all ten sites studied by Haskins and Haskins (1988). At four of the sites, they also found P. megacephala (Table 2). In 2016, I again found L. Aumile at all ten long- term survey sites, but found P. megacephala at only two (Table 2). At Spittal Pond, I found L. /umile at the park entrance and parking lot where P. megacephala occurred in 2002. At Harrington 100s, I found L. Aumile north of Knapton Hill Road as before. South of Knapton Hill Road, rather than P. megacephala, | found high numbers of P. navigans and T. simillimum. At two long-term survey sites, I found both L. humile and P. megacephala: on Ire- land Island and the Newstead Hotel (now Newstead Belmont Hills Golf Resort and Spa). On Ireland Island, I found P. megacephala along the North Breakwater and by the Maritime Museum (now the National Museum) as before. In addition, I collected P. megacephala in front of the Clocktower Mall and to the south end of the Glassworks Mall, two places occupied by L. humile 14 years earlier, indicating a modest expansion of the P. megacephala population on North Ireland Island. At the Newstead Hotel, I found the boundary between L. humile and P. megacephala territory, near the western edge of the property, essentially identical as 14 years earlier. At the Newstead Hotel, I collected in the same vial L. humile and P. megacephala workers from only a few meters apart; the ants immediately locked in battle, confirming their mutual intolerance. I found five ant species nesting in red mangrove in Bermuda: L. /umile plus four Old World exotics that Wetterer and Wetterer (2004) did not collect in 2002: Cardio- condyla minutior, Cardiocondyla obscurior, Monomorium floricola, and Plagiolepis allu- audi (Table 3). At nine of the 14 sites, I found ants nesting inside twigs and branches: Hungary Bay (four samples with MM. floricola, six with P. alluaudi), Crow Lane Park (one with C. obscurior, three with M. floricola), Trott’s Pond (all ten with P. alluaudi), Walsingham Bay (four with M@. floricola, one with C. minutior), Stokes Point Park (two with L. humile), Blue Hole (one with M. floricola), Mill Creek (two with L. hu- mile), The Lagoon (one with L. Aumile), and Pilchard Bay (one with C. obscurior, two with L. humile). Cardiocondyla obscurior and Monomorium floricola are both almost exclusively arboreal species (Seifert 2003, Wetterer 2010). At many red mangrove sites, I saw streams of L. /umile on the branches of red mangrove growing in shallow water. In some cases, L. humile workers I found inside twigs could have belonged to land-based colonies, where they could access the man- Invasive ants of Bermuda revisited 37 Table |. Ants of Bermuda, arranged in descending order of the number of collection sites in 2002 (Wet- terer and Wetterer 2004) plus the number of collection sites in 2016. + = recorded for the first time in 2016. NX = New World exotic. OX = Old World exotic. Species Status Pheidole megacephala 1889-2016 OX Brachymyrmex cf. obscurior Se eT ema native? Brachymyrmex cf. heeri S$, 8 eats. native? Solenopsis sp. thief ant 1934- 2016 native? Paratrechina longicornis en he Se Era OX Hypoponera opaciceps 1905-2016 native? 2016 NX +Pheidole navigans Tetramorium simillimum eee ee ee eee OX Tetramorium caldarium ee ee OX Monomorium floricola 2009-2016 OX Odontomachus ruginodis te a 8922016" native? + Strumigenys membranifera 42,28 OX Camponotus pennsylvanicus 2 2001-2002 NX Cardiocondyla emeryi | tT at 1905-2002 | OX Cardiocondyla obscurior —_2_|__— 1987-2016 OX Monomorium monomorium 1 1900-2016 Ox PAU Aaa a _) eas-2016 | OK + Cardiocondyla minutior 4} 26 OX +Strumigenys emmae 1 2016 OX ET SSS a aan ee Wasmannia auropunctata 1925-1966 NX Nylanderia vividula Pawel 1925 Ox — \o \o NP ARK] HX | CO | CO {unt ON | AN iN Oo Ph | AS | AX Hypoponera punctatissima 1 ip MOTOS on 10 Ox Nylanderia ct. fulva NX Table 2. Ten sites surveyed repeatedly by Haskins and Haskins (1988), Wetterer and Wetterer (2004), and the present study in 2016. P = Pheidole megacephala, L = Linepithema humile, both = both species, - = not surveyed. (See Methods for more detailed site information.) Year a 2016 Great Head Park Mullet Bay Rd. & Ferry Road Leamington Caves Knapton Hill Rd Intersection Knapton Hill Rd & Harrington 100s Christchurch & Brighton Hill 1g i Spittal Pond ae eee Newstead Hotel =f} | both both | sen Wreck Road — Ireland Island al bd % observations = P. megacephala te Partita) Fat eS cm 38 James K. Wetterer / Journal of Hymenoptera Research 54: 33-41 (2017) Table 3. Ants nesting in dead twig and branch samples from red mangrove, arranged in descending order of number of collection sites. # sites # samples 12 i sites 4 4 Plagiolepis alluaudi 16 Monomorium floricola Linepithema humile Cardiocondyla obscurior Z Cardiocondyla minutior 1 grove growing in water via a continuous canopy. However, one sample from Pilchard Bay that had L. Aumile inside twigs came from a small mangrove island consisting of two mangrove trees isolated by water from all other mangroves. This L. humile colony had to be completely arboreal. All three samples that people sent me from their houses included L. humile. One also included P. megacephala and Brachymyrmex cf. heeri, and one included P. navigans. Discussion In 2016, I found that ZL. Aumile dominated most sites I surveyed in Bermuda. Still, P megacephala occupied substantial areas, particularly in and around the capital of Hamilton. Pheidole megacephala is a dominant species in tropical sites around the world, whereas Linepithema humile tends to dominate in subtropical areas with “Medi- terranean’ climates. It appears that L. Humile may be better suited to the subtropical cli- mate of Bermuda, except perhaps in warmer and sunnier habitats, such as the plantings along urban streets and in open parks, where P megacephala may have the advantage. One ant species that is possibly native to Bermuda is the trap-jaw ant Odontoma- chus ruginodis. This species was once common in Bermuda, but now appears to be quite rare (Haskins and Haskins 1965). Odontomachus ruginodis is common in South Florida and the West Indies. Although it is not known as a tramp species, Deyrup (1992) considered it to be probably exotic to Florida. Genetic analyses could help de- termine whether Odontomachus ruginodis (or any other ant species) is native or exotic to Bermuda. Bermuda has the northernmost populations of mangroves in the world (Spalding et al. 2010). I surveyed ants in the red mangroves of Bermuda in the hope of finding some rare ants that use this unique habitat as a refuge and thus escaped extermina- tion by P. megacephala and L. humile. However, because L. humile also nests in red mangrove, this habitat did not provide a refuge for ant species incapable of co-existing with this dominant species. Except for L. Humile, all ant species I found nesting in the red mangroves of Bermuda were Old World exotics. Thus, red mangroves may serve as a refuge from the dominant invasive ants, but the only ants taking advantage of this refuge are other exotic species. Invasive ants of Bermuda revisited 39 In the absence of invader-free refuges, invasive ants can drive native species to ex- tinction. For example, in 2003, I surveyed ants on Monte Gordo, the highest mountain of the Atlantic island of Sao Nicolau, Cape Verde, and found only P. megacephala at all sites sampled except for sites within 100 m of the mountain’s peak J KW, unpublished data). Here, where P. megacephala had not yet spread, a small pocket of other ant species survived, including an endemic species known only from this mountain, Monomorium boltoni. If P. megacephala continues its spread up the mountain, it seems unlikely that M. boltoni will survive once P. megacephala overruns what may be its last refuge. Simi- larly, it may be that all ant species originally native to Bermuda are now extinct. I was surprised to collect P. navigans at five sites scattered across Bermuda (and I was sent specimens from a sixth site), given that this species had never before been collected in Bermuda, and that I surveyed three of these same locales in 2002. This suggests that P. navigans may be a recent arrival on Bermuda and is spreading quickly. Curiously, at four of the five sites, P. navigans was coexisting with L. humile. On Ordnance Island, I even found them nesting together under the same piece of con- crete. It would be interesting to determine whether or not P. megacephala can tolerate P. navigans. Pheidole navigans, a big-headed ant native to the Neotropics, is known as an exotic in the southeastern US (formerly misidentified as P. moerens; see Sarnat et al. 2015). If P. navigans battles with P. megacephala, but not with L. humile, the presence of P. navigans could affect the competitive balance between P. megacephala and L. humile. Pheidole megacephala and L. humile began their worldwide dispersal in the 19th century and have already spread through much of their potential range (Wetterer et al. 2009; Wetterer 2012). However, several other highly destructive ants have thus far come to occupy only a small portion of their potential ranges, most notably the red im- ported fire ant (Solenopsis invicta) (Wetterer 2013). Great vigilance is needed to prevent S. invicta and other invasive ant species from reaching Bermuda where it would likely thrive (Morrison et al. 2004) and cause substantial ecological and economic damage. Acknowledgments I thank M. Wetterer for comments on this manuscript; L. Greene, C. Jessey, and S.R. Smith for help and hospitality in Bermuda; R. Franco, J. Steele, and C. Stringer for sending me samples from their homes; Florida Atlantic University for financial support. References Crowell KL (1968) Rates of competitive exclusion by the Argentine ant in Bermuda. 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Florida Entomolo- gist 87: 212—221. http://dx.doi.org/10.1653/0015-4040(2004)087[0212:AHFOB]2.0.CO;2 Wetterer JK, Wetterer AL, Hebard E (2001) Impact of the Argentine ant, Linepithema humile (Mayr), on the native ants of Santa Cruz Island, California. Sociobiology 38: 709-721. Wetterer JK, Wild AL, Suarez AV, Roura-Pascual N, Espadaler X (2009) Worldwide spread of the Argentine ant, Linepithema humile (Hymenoptera: Formicidae). Myrmecological News 12: 187-194. Wheeler WM (1906) The ants of the Bermudas. Bulletin of the American Museum of Natural History 22: 347-352. Invasive ants of Bermuda revisited 4] Supplementary material | Specimen collection information Authors: James K. Wetterer Data type: specimens data Explanation note: Self-explanatory Copyright notice: This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODDbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.