Nylanderia

Several Nylanderia species have been reported as being tramps. For example, N. bourbonica and N. vaga are commonly encountered in the tropics and subtropics and have spread across large areas. Infestations can involve smaller areas, although population sizes can be very large, as with N. pubens (Caribbean crazy ant) in the Caribbean. A Nylanderia species has invaded Texas and several other states in Southeastern United States in a sudden, explosive outbreak. Several other species in the genus have also been reported as introduced outside their native range, including N. clandestina, N. flavipes, N. fulva (Rasberry crazy), N. guatemalensis, and N. vividula.[15]

Workers are generally monomorphic, although some species are variable in size, with a possible example of worker polymorphism observed in N. amblyops from Madagascar.[11] Nylanderia workers can generally be easily distinguished from other formicines based on the presence of six 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 six 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, LaPolla, Brady & Shattuck 2011 (2011) interpreted the presence of macrosetae on the propodeum within Nylanderia as having arisen independently from those observed in other closely related genera.[18]

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. Five teeth are present in Euprenolepis queens and five or fewer in Pseudolasius, while Nylanderia possesses six (or rarely seven) teeth. In other genera such as Paratrechina and Paraparatrechina, 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 distinguishes them from Nylanderia.[19]

Males of Nylanderia can be more difficult to distinguish from other Prenolepis genus-group genera because considerable variation occurs 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 one or two 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 have reduced labial and maxillary palp numbers from the more typical six maxillary and four 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. 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.[19]