Nylanderia

The genus Nylanderia (Formicidae: Formicinae) is a large, ecologically important ant genus with a nearly cosmopolitan distribution. It currently is comprised of over 130 extant species and subspecies and two fossil species. Until recently most Nylanderia species were placed in the genus Paratrechina. Molecular phylogenic studies and a reassessment of morphological characters has led to the resurrection of Nylanderia as a valid genus. These ants live in habitats that range from deserts to rainforests and nest in leaf litter, soil, or in rotten wood. Most species are epigaeic, generalist foragers (LaPolla et al., 2011a).

Identification
Mandible with 6 to 7 teeth; maxillary palps 6-segmented; labial palps 4-segmented; erect setae on dorsum of head randomly placed; typically with abundant erect setae on head, scapes, legs and dorsum of mesosoma, although a few species lack erect setae on head, scapes and legs. Eyes typically well developed and placed midlength and laterally on head. Dorsal mesosomal setae arranged loosely in pairs; propodeum lacking erect setae (with one exception); propodeum with a low- to high-domed dorsal face; generally overall mesosoma shape compact.

Nylanderia workers can generally be easily distinguished from other formicines based on the presence of 6 mandibular teeth, erect macrosetae on the scapes and legs, and paired erect macrosetae on the pronotum and mesonotum. These morphological features are considered synapomorphies for the genus, and will effectively separate this genus from other genera. Overall, the body shape for most Nylanderia workers is compact and robust in that the mesosomal regions are generally short (as measured against the long axis of the body) and relatively high when compared to a species such as Paratrechina longicornis. There are, however, several species where the mesosoma is more elongated, superficially resembling Paratrechina longicornis. Long erect macrosetae are almost never found on the dorsal face of the propodeum, with one known exception. However, species with an elongated mesosoma or short propodeal macrosetae do possess 6 mandibular teeth, erect macrosetae on the scapes and legs, and paired erect macrosetae on the pronotum and mesonotum which support their placement within Nylanderia based on the definition of the genus proposed above. Additionally, when macrosetae are present on the propodeum they show a pattern generally similar to that found on the pronotum and mesonotum of Nylanderia, with the macrosetae being numerous and of varying lengths. This is in contrast to related genera, for example Paraparatrechina, where the macrosetae are limited to a single, distinct pair. Given the differences in the patterns of these macrosetae among these genera, and when considering additional characters as outlined above, we interpret the presence of macrosetae on the propodeum within Nylanderia as having arisen independently from those observed in other closely related genera.

The main features used to distinguish Nylanderia queens from other Prenolepis genus-group genera come primarily from the mandibles and scapes. Like workers, Nylanderia queens have erect macrosetae on their scapes. However, the macrosetae are often not as distinct as in workers because the macrosetae are often shorter and usually surrounded by a thick layer of decumbent pubescence. When considering genera such as Euprenolepis and Pseudolasius in which queens also possess macrosetae on the scapes, differences in mandibular tooth count will distinguish Nylanderia queens. There are 5 teeth present in Euprenolepis queens and 5 or fewer in Pseudolasius (LaPolla 2009; LaPolla et al. 2010a) while Nylanderia possesses 6 (or rarely 7) teeth. In other genera such as Paratrechina (LaPolla et al. 2010a) and Paraparatrechina (LaPolla et al. 2010b) the queens have no erect macrosetae on their scapes. For Prenolepis, if erect macrosetae are present on the scapes, the more posterior placement of the eyes will distinguish them from Nylanderia.

Male Nylanderia can be more difficult to distinguish from other Prenolepis genus-group genera because there is considerable variation in the genitalic structures at the species-level for all genera, and features such as mandibular dentition are not useful since dentition is always reduced in males from that observed in workers and queens (usually to 1 or 2 teeth). The scapes can be useful in separating male Nylanderia from some Prenolepis genus-group genera since they possess macrosetae similar to those found in workers and queens, but at reduced numbers. Paratrechina and Paraparatrechina males, like workers and queens of these genera, never have macrosetae on their scapes. In general Nylanderia males have subtriangular parameres, but similar shaped parameres are also seen in some species of Euprenolepis, Prenolepis, and Pseudolasius. Both Euprenolepis and Pseudolasius (LaPolla 2009) have reduced labial and maxillary palp numbers from the more typical 6 maxillary and 4 labial palps observed in other Prenolepis genus-group genera. For Prenolepis the separation of males from Nylanderia is unclear, largely because for the vast majority of Prenolepis species the males are unknown. Caribbean Zatania (once thought to be Prenolepis0 have parameres that are distinct from Nylanderia in that they are extremely long and thin. Separation of the widespread North American Prenolepis imparis from Nylanderia  is based on the extremely short scapes (not much longer than the head) that lack macrosetae.

Although most species of this genus are easily recognizable, there are several Nylanderia species (such asNylanderia otome and Nylanderia yambaru) that superficially resemble Paraparatrechina in that they lack erect setae on the legs and/or scapes and have paired erect setae on the pronotum and mesonotum. Scapes without erect setae or with very few setae appear more commonly in New World Nylanderia (particularly among the North American species), with the condition only spottily observed for species outside this region. However, essentially all species can be placed into Nylanderia based on the lack of erect setae on the propodeum and the presence of six mandibular teeth. The single known exception is an undescribed species from Papua New Guinea, which has numerous elongate setae on the propodeum. However, in this case the setae differ in number and structure from those found in other genera considered here. Undoubtedly, as taxonomic revision of Nylanderia progresses there will be some adjustments regarding to which genus a few species are ascribed, so the generic species list reported below will probably change in the future. (LaPolla et al. 2010)

Africotropical
species key - La Polla et al. 2011

La Polla et al. (2011) - The Afrotropical Nylanderia fauna comprises 14 native species (and 3 introduced species) that display a wide range of morphological variation. For example, propodeal shape provides a key diagnostic feature for many species. Species such as Nylanderia lepida and Nylanderia impolita have strongly convex, dome-like dorsal faces of the propodeum, while species such as Nylanderia boltoni and Nylanderia umbella have very short, angular dorsal faces of the propodeum. Coloration ranges from light brown to yellowish colored workers as observed in Nylanderia incallida and Nylanderia luteafra to dark brown workers as observed in N. lepida and Nylanderia mendica. All castes of one species, Nylanderia silvula, are a deep reddish-brown (males and queens are darker than workers), an unusual coloration for Nylanderia species. Another interesting feature of several Afrotropical Nylanderia is that they display cuticular rugulae; globally, the vast majority of Nylanderia species have smooth cuticles. The species Nylanderia brevisetula, N. incallida, N. impolita, and N. mendica all possess rugulose cuticles, particularly on the head and mesopleuron. One species, N. mendica, stands out because it possesses distinct striations on the dorsum of the gaster.

Males are known in only a few Afrotropical Nylanderia species, but these show an interesting degree of morphological diversity in the genitalia, particularly the digiti and cuspi. While N. boltoni, N. lepida, Nylanderia natalensis, and N. silvula all have similar digiti and cuspi that are not particularly different from what is observed in male Nylanderia from other parts of the world, the digiti and cuspi of Nylanderia jaegerskioeldi and Nylanderia waelbroecki are highly distinctive. Digiti are typically larger than the cuspi in Nylanderia species. In these two species the digiti are blade-like and smaller than the cuspi, which are much larger and unusually shaped. In N. jaegerskioeldi the cuspi are rounded distally and paddle-like with many teeth on the ectal surface. In N. waelbroecki the cuspi are horn-like, with a distal extension of the structure.

Neartic
species key - Kallal & LaPolla 2012

Kallal & LaPolla (2012) - The fauna in the Nearctic region is comprised of 14 native species and 5 introduced species. This constitutes a relatively small percentage of the Nylanderia species of the world (LaPolla et al., 2011a). In the Nearctic, observed worker morphological variation lies primarily in overall setation and pubescence patterns. Although most species have relatively sparse pubescence on the mesosoma, this is variable, and introduced species may be broadly recognized by the presence of denser mesosoma pubescence. Males are typically pubescent on the dorsum and queens are uniformly pubescent, as is common in Nylanderia queens from other parts of the world. Cephalic pubescence varies greatly across the species, from virtually absent to being very dense. Coloration ranges from what is perhaps the palest ant in the world, Nylanderia phantasma, to dark brown, as in Nylanderia parvula. Hues of brown and yellow are very common, and multiple species have contrasting mesocoxae and metacoxae as compared to their mesosoma. Males and queens are frequently a little darker than workers of the same species. Cuticular sculpturing is not observed in any Nearctic species.

Males of Nearctic Nylanderia are the best known of any the world’s faunas, with males associated with every species. Given the morphological similarities in the worker caste, the value of male characters cannot be overstated. Paramere shape varies from triangular as is seen in most species to being digitiform, as in Nylanderia bruesii. The digiti are typically about twice as long as the cuspides. The aedeagal valves are similarly convergent with a general triangular shape common in virtually all species. Finally, dissection of the genitalia reveals wide variation in the shape of the ninth sternite, suggesting this feature may be of more value than has been suggested in past works on the genus (Krafchick, 1959).

South Pacific
List and montage images of South Pacific Nylanderia species.

Distribution
Found in all geographic regions with the exception of high latitude areas.

LaPolla et al. (2010) - This genus is essentially worldwide in distribution, but its exact northern limits are uncertain, and it is curious that apparently no native species are found in Europe. The genus reaches its highest diversity in the tropics, but in many temperate areas Nylanderia form important components of the fauna (Ward, 2000). Humans have dispersed a few species around the globe, and there are several economically important invasive species in this genus.

Habitat
Nylanderia species inhabit a wide array of habitats from deserts to rainforests, although they reach their highest species diversity in forested and warmer environments.

Biology
Nylanderia are among the most abundant ant species in many places where the genus occurs. For example, Ward (2000) found that Nylanderia (recorded as Paratrechina) was the fifth most frequently encountered ant genus in leaf-litter samples from around the world. They are efficient and rapid foragers and often find resources (e.g. baits) first to which they can recruit rapidly, but rarely can defend a resource against other ants that arrive later to baits (J. Longino, pers. comm.). Most are conspicuous, epigaeic generalist species that form large, polydomous nests. Frequent nest movements are known for some species, especially those that nest in leaf litter and rotting wood. For example, Nylanderia bourbonica can nest opportunistically in temporary sites that are habitable for only a few days or weeks (Hölldobler and Wilson 1990). The small (125–150 individuals) colonies of Nylanderia faisonensis also inhabit ephemeral locations in the leaf litter or soil of hardwood forests (Lynch et al. 1980, identified incorrectly as Paratrechina melanderi). A few more morphologically specialized species exist, such as the sand-dwelling Nylanderia arenivaga and Nylanderia phantasma from the southeastern United States, several small-eyed species such as Nylanderia microps from Puerto Rico, and several undescribed species from Australia. There are at least three currently undescribed workerless social parasites known from the eastern United States (Cover, LaPolla, Brady unpublished).

In temperate areas most Nylanderia species produce reproductives during the summer, which overwinter in the nest to then emerge early the following spring; Nylanderia species are typically among the first ant reproductives to fly (Trager 1984; Ichinose 1987) after Prenolepis. However, we know little about the reproductive biology of many Nylanderia species, especially those inhabiting the tropics. Cases of polygyny have been noted among Nylanderia species (Frumhoff and Ward 1992; Arcila et al. 2002), but how widespread this condition is within the genus remains unclear. At least one species, Nylanderia flavipes, is somewhat unusual among ants in having populations that are both monogynous and polydomous (Ichinose 1986).

Several Nylanderia species have been reported as being tramps. For example, Nylanderia bourbonica and Nylanderia vaga are commonly encounteredin the tropics and subtropics and have spread across large areas (Klotz et al. 1995; Wilson and Taylor 1967; Wetterer 1998). Infestations can involve smaller areas, although population sizes can be very large, as with Nylanderia pubens in the Caribbean (Wetterer and Keularts 2008). An unknown Nylanderia species has invaded Texas and several other states in the American southeast in a sudden, explosive outbreak (Gotzek, Brady, Kallal, LaPolla, in prep). Several other species in the genus have also been reported as introduced outside their native range, including Nylanderia clandestina, Nylanderia flavipes, Nylanderia fulva, Nylanderia guatemalensis, and Nylanderia vividula (McGlynn 1999). However, it is important to note that species identifications within Nylanderia are often suspect given the taxonomic uncertainties that have befuddled so many who have worked on the genus. Additionally, the identities of some reportedly invasive species, such as N. bourbonica and P. vaga, have never been clarified, leaving accurate identifications difficult or impossible. Preliminary results suggest that while several Nylanderia have spread through human activity, the names used for these taxa may be in error. Because of this situation, even creating an accurate list of invasive species within the genus is currently impossible and will only be achievable when a comprehensive revision of the group has been completed. But even without reliable identifications, it would appear that “invasiveness” has originated multiple times within Nylanderia. The broad-scale phylogeny of LaPolla et al. (2010a) suggests at least four separate origins of invasive species, but denser taxon sampling and refinement of taxonomy will be necessary for a more accurate total.

Africa
La Polla et al. (2011) - Nylanderia species are found throughout the continent of Africa, with the majority of species being found in the equatorial rainforests. Three species are found outside of rainforest habitats: Nylanderia natalensis in southern Africa; Nylanderia boltoni in western, eastern and southern Africa; and the far ranging Nylanderia jaegerskioeldi in eastern, northern, and western Africa. Nylanderia jaegerskioeldi is of particular interest because it appears to be the only Afrotropical species that occurs outside of this biogeographic region, ranging into the Palearctic (North Africa and, perhaps, the northern Mediterranean region). Afrotropical Nylanderia species are apparently absent from much of the southern deserts of the continent, and it is particularly surprising that there do not seem to be any endemic species found in the Western Cape Province of South Africa, an area known for high insect endemism. All three authors have collected in the Western Cape, but failed to find new species of Nylanderia there.

Nearctic
Kallal & LaPolla (2012) - Nearctic Nylanderia species have been collected from southern Canada in the north to central Mexico in the south. Habitats range from deciduous forests to subtropical scrub to arid deserts. Virtually no collections of native species have been recorded from the northwest. Species richness appears to be highest in the southeastern United States. The presence of new species in relatively well collected areas of the Nearctic (for example, the highlands of the central United States and the deserts of the southwestern United States) is surprising, and is indicative of the need for continued collecting of this genus even in well studied areas.

Reproductives are reared in the summer, overwinter as adults, and fly in the first warm, humid days of spring and summer (Trager, 1984; Ichinose, 1987). More exact dates of flights vary based on local climate, and some species in regions that are warm year round may fly at any time (Trager, 1984). Nests are typically found in leaf litter and rotting wood, although some species are known to have specific habitat requirements, including white sand for Nylanderia phantasma and marshes for Nylanderia concinna. Nests may be permanent or temporary, with the latter as in Nylanderia terricola in forest leaf litter (Lynch et al., 1980). There are three known, but undescribed, workerless social parasite Nylanderia species that will be published at a later date (Cover et al., in prep).

Introduced, non-native species are known in the Nearctic region, having been introduced from both Asia and the Neotropics. The species Nylanderia bourbonica, Nylanderia steinheili, Nylanderia pubens, and Nylanderia fulva can be found in the Gulf states, particularly Texas and Florida. Nylanderia fulva is an aggressive invasive that successfully colonized multiple Caribbean islands before arriving in the United States. It appeared first in Texas but has likely spread throughout the entire southeastern part of the country (Gotzek et al., 2012). Workers of this species are impossible to separate from another introduced species, Nylanderia pubens. At this time it appears N. pubens has only been introduced to Florida. Nylanderia flavipes was introduced from Asia in the early 1900’s and has since colonized much of New England and the Mid-Atlantic, particularly in urban areas. It appears to be displacing the native species, Nylanderia faisonensis, in some places (Trager, 1984; Wetterer, 2011). Another species,Nylanderia guatemalensis, has not been found in the Nearctic, despite previous reports of its presence in the region (Trager, 1984). Given its widespread distribution across the Caribbean, and suspected invasive habit, it has the potential to be an invasive species in the Nearctic region.

Nomenclature

 *  NYLANDERIA [Formicinae: Plagiolepidini]
 * Nylanderia Emery, 1906b: 133 [as subgenus of Prenolepis]. Type-species: Formica vividula, by original designation.
 * Nylanderia subgenus of Paratrechina: Emery, 1925b: 217; Creighton, 1950a: 405; Smith, D.R. 1979: 1443.
 * Nylanderia raised to genus: Wheeler, W.M. 1936b: 210; Kempf, 1972a: 166.
 * Nylanderia junior synonym of Paratrechina: Trager, 1984b: 51.
 * Nylanderia revived from synonymy, status as genus: LaPolla, Brady & Shattuck, 2010a: 126.
 * Nylanderia senior synonym of Andragnathus: LaPolla, Brady & Shattuck, 2010a: 126.
 * ANDRAGNATHUS [junior synonym of Nylanderia]
 * Andragnathus Emery, 1922d: 111. Type-species: Andragnathus hubrechti, by monotypy.
 * Andragnathus junior synonym of Paratrechina: Agosti & Bolton, 1990a: 75.
 * Andragnathus junior synonym of Nylanderia: LaPolla, Brady & Shattuck, 2010a: 126.

Worker

 * Small to medium sized (generally between 1.0–4.0 mm in total length [defined as: head length + Weber length + gaster length]) formicine ants ranging in color from pale yellow to black; cuticle usually smooth and shining, but sculpturing present in several African species.


 * Mandibles typically with 6 or, rarely, 7 teeth present; palp formula 6:4 except in N. dodo which is 5:3.


 * Clypeus subrectangular, medially convex, with scattered erect setae.


 * Antennae 12-segmented; scapes surpass posterior margin of head; scapes with erect macrosetae and a layer of pubescence.


 * Eyes usually well developed (although small-eyed species are known), placed midlength or anterior and laterally on head; ocelli often absent, but when present, indistinct.


 * Sides of head parallel or gently convex, merging into broadly rounded posterior corners.


 * Posterior margin straight or medially convex.


 * Pronotum typically broadly convex; in lateral view, pronotal margin convex and then leveling off towards the mesonotal margin; in a few species pronotal margin nearly flat in lateral view; macrosetae on pronotum variable, although often with two pairs of long erect macrosetae and scattered shorter erect setae.


 * Mesonotum typically flat to slightly convex; mesonotum with scattered erect macrosetae (often with two pairs of long erect macrosetae and scattered shorter erect setae).


 * Propodeum shape variable; dorsal face can be slightly convex but fairly short, short and angular, or strongly convex and dome-like; propodeum always lacking erect macrosetae, although a fringe of pubescence often present on anterior of propodeum (one known exception, an undescribed species from Papua New Guinea).


 * Legs with abundant, scattered macrosetae.


 * Petiole wedge-shaped (cuneate), never surpassing the height of the propodeum in lateral view, although in some species it approaches height of propodeum.


 * Gaster large and oval shaped, becoming pointed distally towards acidopore; usually with abundant, scattered erect macrosetae and often a layer of pubescence.


 * Petiolar foramen long, extending beyond the anteriormost points of the metacoxal cavities.

Queen

 * Generally as in worker with modifications expected for caste.


 * Eyes large and conspicuous, with three well developed ocelli.


 * Mandibles with 6 or, rarely, 7 teeth present.


 * Scapes generally shorter relative to head length than observed in conspecific workers.


 * Typically most of cuticle covered in a dense layer of pubescence; scattered macrosetae found on scapes, head, pronotum, mesonotum, legs and gaster; general body color often darker than workers.


 * Mesosoma large, with collar-like pronotum and overarching mesonotum.


 * Mesonotum large and flat, typically with scattered macrosetae.


 * Propodeum typically with short, subangular dorsal face, even in species with a long dorsal face in the worker.


 * Gaster very large, with scattered macrosetae.

Male

 * Sculpture and color pattern of males generally approaching those of workers.


 * Mandibles well developed with a prominent apical tooth and often a small, basal tooth (or just a pronounced basal angle), with smaller denticles present along masticatory margin in some species.


 * Scapes long, surpassing posterior margin of head; antennae 13-segmented.


 * Eyes large and conspicuous, with three well developed ocelli.


 * Mesosoma large, with collar-like pronotum and overarching mesonotum.


 * Mesonotum large and flat, typically with scattered macrosetae.


 * Propodeum inconspicuous, with very short dorsal face.


 * Genitalia prominent; parameres often subtriangular in appearance; digiti and cuspi highly variable; 9th sternite often obscured by 8th sternite in which case it is only visible with dissection.