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Ants of Horn Island, Jackson County, Mississippi
Joe A. MacGown and Timothy Lockley
June 2017

       Horn Island is an elongate, thin barrier island that is located off the Gulf Coast of Jackson County, Mississippi. The island is several miles long, but it is less than one mile wide at its widest point, and in total occupies approximately 11 square kilometers. Although other islands (Petit Bois, Ship, and Cat Island) also comprise the Mississippi Barrier Islands, Horn Island is the largest and the most undeveloped. Sevreral distinct habitats are found on the island including sand dunes, small groves of long leaf pines, and inland lagoons.
       The ant fauna of Horn Island was not studied extensively, and was limited to some pitfall traps, bait traps, and blacklight traps. Due to the nature of the trapping, extensive information on behavior and microhabitat is not available. However, enough information about the foraging species was gathered to make it worth while to document these findings. The research was conducted primarily from 1999-2002 by Lockley, and specimens were later identified by MacGown. These collections predate Hurricane Katrina in late August 2005. It is not known what the long term effects of the hurricane were on the ant fauna, although it likely had some negative impact on some of the more sensitive species.
       Three species of Dorymyrmex, D. bureni (Trager), D. flavus McCook, and D. grandulus (Forel) were collected on the island. Members of this genus, which are in the subfamily Dolichoderinae, are typically associated with sandy soils. Dorymyrmex bureni is a widespread species in the Southeast and is not confined to coastal localities. This is a large, yellow to yellowish brown species, that has a convex shaped promesonotum, does not have an angulate mesonotal declivity, and has a strong propodeal cone. Until recently, Dorymyrmex flavus was thought to be a western species. This species extends into Mississippi along the Mississippi River down to at least the coast of Alabama. It is similarly colored to D. bureni, but has a flatter promesonotum with a distinct mesonotal declivity (in profile view), and also has a strong propodeal cone. Dorymyrmex grandulus is a sand inhabiting species that is found mostly in coastal locations in the Southeast from North Carolina to Mississippi. This species is smaller than the previous mentioned species, is dark brownish black, also has a somewhat flattened promesonotum with a distinct mesonotal declivity (in profile view), and a much reduced propodeal cone. Another common dolichoderine ant, Forelius pruinosus Roger, that prefers areas of deep sand was collected in great numbers on the island. This small, dark reddish brown to brownish black ant is smaller than Dorymyrmex species and lacks a propodeal cone.
       Two species of Brachymyrmex, B. depilis Emery and B. patagonicus Mayr were collected on the island. Brachymyrmex depilis is a native species that is common in soil. Workers of this species were not collected, but alate females were collected at a blacklight trap. Workers are minute, yellow in color, and have nine segmented antenna. Brachymyrmex patagonicus is an exotic species native to Argentina that is becoming increasingly common in the southeastern U.S. Workers of this species are minute and dark brown to brownish black in color.
       Only one species of Nylanderia, N. phantasma Trager, was found on the island, and it represented a new state record for Mississippi. This is a small species that nests in open sand and is active nocturnally. Workers are pale yellow and the antennal scapes have only 2-4 erect hairs, which separates them from other related species.
       Three different carpenter ants were collected including Camponotus castaneus (Latreille), C. floridanus (Buckley), and C. nearcticus Emery. Camponotus castaneus is a widepread species that typically nests in the soil, although it occasionally nests in rotting wood. Mature colonies are large. Workers are large and orangish red in color. Camponotus floridanus, the Florida carpenter ant, is much less widely distributed and is mostly confined to coastal areas, where it nests in large colonies in rotting wood. It is an occasional pest of wood products in Florida, where it is more common. In Mississippi, it has only been reported from Jackson County, and recent collections have been confined to Horn Island. This large species is bicolored red and black and has abundant pilosity on the entire body. Camponotus nearcticus is another widespread species, but it typically nests in cavities with colony size usually being somewhat small. This species is smaller than the previous two and is concolorous, shiny black.
       Only one ponerine ant, Hypoponera opacior (Forel), was collected in the traps. This small brown species is very common in litter is found in a wide variety of habitats. Two species of fungus growing ants, Cyphomyrmex rimosus (Spinola) and Trachymyrmex septentrionalis (McCook) were collected on the island. Cyphomyrmex rimosus is an introduced species from South America that is now common and abundant in the Southeast. Colonies are usually small and hidden. Workers are not aggresive and curl up and lie motionless when disturbed. They are an opaque grayish black in color and have rounded projections on the body. Trachymyrmex septentrionalis is a native widespread species. Colonies tend to be slightly larger than in Cyphomyrmex. They can be recognized by their reddish brown color and their irregular projections on the body. Both of these species grow underground fungus gardens, which they use for sustenance.
       Three species of Solenopsis, S. carolinensis Forel, S. globularia littoralis Creighton, and S. invicta were found. The first species, S. carolinensis, is a minute soil dwelling species that is common in Florida, southern Alabama, and Mississippi. This species is in a very taxonmically challenging group and the presence of queens greatly aid the identifiction process. Fortunately, at least some queens were collected in the blacklight traps. Solenopsis globularia littoralis appears to be restricted to coastal areas in the Southeast. This small species can be recognized by its extremely large postpetiole. Solenopsis invicta, the imported red fire ant, is now common throughout much of the Southeast, although it thrives in disturbed habitats. Based on the number of individuals collected in the trap samples, this species appears to be abundant on Horn Island.
       The Florida harvester ant, Pogonomyrmex badius (Latreille), was very common in trap samples and was apparently doing quite well on the island. Historically, this species, which nests in areas of deep sand, was reported from many parts of Mississippi, but had not been found on the mainland over 70 years despite being actively searched for. It has been suggested that the large quantities of aerially applied pesticides aimed at killing the introduced fire ant played a significant role in its apparent dissappearance. Further boosting this theory was the fact that Horn Island was one of the few places in the state that did not receive the pesticidal applications, and also the only known locality where this species still survived. However, recent collections by the Mississippi Entomological Museum have resulted in the rediscovery of this species on the mainland of the state in a relic sandhill habitat in Smith County. Pogonomyrmex badius is the only member of the genus found east of the Mississippi River. It makes nests up to three meters deep, which are surmounted by low mounds or craters. The mounds, which may be 40 cm or more in diameter, are often covered with many small pieces of charcoal, seed husks, various pieces of debris, and sometimes small pebbles. Due to the large size and adornment of the mounds, they are very easy to spot in the field. At night workers of this diurnal species close the entranceways to their deep subterranean nests. Workers are reddish brown and range in size from 0.64 to 0.95 cm. The largest workers have huge heads. Seeds of various grasses and forbs form a large part of the diet of harvester ants, although they supplement their diet with various arthropods. Members of this genus are reputed to have among the most painful sting of any North American ant, and although they are not overly aggressive, special care should be taken to avoid being stung by them.
       Only two species of Pheidolini (subfamily Myrmicinae), Aphaenogaster ashmeadi Emery and Pheidole moerens Wheeler, were collected in the traps. Aphaenogaster ashmeadi has limited distribution in the Southeast and appears to be limited to counties near the coast. It is a relatively large, reddish brown, long legged species that has a distinctive flattened lobe on the basal portion of the antennal scape that occupies less than one-fifth of the scape length. The only other species of Aphaenogaster with a similar lobe in the eastern U.S. is A. treatae, but the flattened area is longer, usually at least one-fourth of the scape length. Pheidole moerens is an introduced species from South America that is now very common in parts of the Southeast. In Mississippi it is most common in the southern third of the state, although its range appears to be expanding. Eastern species of Pheidole are dimorphic and have a minor and major worker class, with the majors being much larger and having proportionally large heads. Workers of P. moerens are relatively small and reddish brown in color.
       Several workers of Crematogaster pilosa Emery were collected in the traps. This is a common species that nests in hollow stems and twigs or other cavities. Workers have a distinctive heart shaped gaster, elongate propodeal spines, and range in color from brownish black to bicolored red and black.
       The total of 20 species collected in traps is not exceedingly high, but not unusual for a restricted habitat that is prone to hurricanes and other severe weather. Nevertheless, it is likely that other more cryptic species are present on the island, which could be collected by litter sampling, baiting trees, or other methods. Four of the species that were collected, Brachymyrmex patagonicus, Cyphomyrmex rimosus, Solenopsis invicta, and Pheidole moerens, are considered to be exotic, and potentially may have out competed some native species. However, three of the species collected, Nylanderia phantasma, Solenopsis globularia littoralis, and Pogonomyrmex badius, are species that tend to typify healthy ecosystems. The collection of N. phantasma represents a new state record for Mississippi, and thus far this is the only known locality for this species in the state. Several of the species collected are restricted to habitats with sandy soils including Dorymyrmex bureni, D. flavus, D. grandulus, Forelius pruinosus, N. phantasma, S. g. littoralis, P. badius, and Aphaenogaster ashmeadi.
       The habitat on Horn Island is similar to that of the Bon Secour National Wildlife Refuge in Baldwin County, Mississippi and, not surprisingly, it has a similar ant fauna as well (Bon Secour ants). Horn Island has the following species in common with Bon Secour N.W.R.: D. bureni, D. grandulus, F. pruinosus, B. depilis, B. patagonicus, N. phantasma, C. floridanus, H. opacior, T. septentrionalis, S. carolinensis, S. invicta, P. badius, and P. moerens. To compare the species of ants from Horn Island to other localities with similar habitats, click on the links below under the heading "links to ants of other sandhill or sand dune habitats".

Ants from Horn Island
Species are arranged alphabetically by genus

Aphaenogaster ashmeadi Emery
Brachymyrmex depilis Emery
Brachymyrmex patagonicus Mayr Exotic
Camponotus castaneus (Latreille)
Camponotus floridanus (Buckley)
Camponotus nearcticus Emery

Crematogaster pilosa Emery
Cyphomyrmex rimosus (Spinola) Exotic
Dorymyrmex bureni (Trager)
Doryrmyrmex flavus
grandulus (Forel)
Forelius pruinosus Roger
Hypoponera opacior (Forel)
Nylanderia phantasma (Trager)
Pheidole navigans Forel Exotic
Pogonomyrmex badius (Latreille)
Solenopsis carolinensis Forel
Solenopsis globularia littoralis Creighton
Solenopsis invicta Buren Exotic
Trachymyrmex septentrionalis (McCook)

Links to ants of other sandhill or sand dune habitats

Ants of Deaton Preserve, Greene County, Mississippi
Ants of Horn Island, Jackson County, Mississippi
Ants of Palestinean Gardens, George County, Mississippi
Ants of Bon Secour National Wildlife Refuge, Baldwin County, Alabama
Ants of Fall Line Sandhills Natural Area, Taylor County, Georgia
Ants of Ohoopee Dunes Natural Area, Emanuel County, Georgia
Ants of Big Hammock Natural Area, Tattnall County, Georgia