Aphaenogaster of Virginia

Aphaenogaster is an extremely ecologically important genus that spreads across many continents. In eastern North America, many species of Aphaenogaster dominate undisturbed/slightly disturbed habitats and are essential for the spreading of myrmecochorous plants. Many species will contribute in the decomposition of rotting wood by creating nests in them. Additionally, the sheer amount of insects that they scavenge from their surrounding habitat helps to keep the ecosystem in check. In captivity, their feeding responses are mind-blowing, the queens pump out eggs, brood grows at a moderate speed, the colonies don't get too big or too small, many species are very good solitary hunters, and they do well with as much or as little food that the keeper provides. In the wild, the many species fulfill so many different niches in so many habitats and is one of the most widespread genera in eastern North America. I feel as if they are very unappreciated in the ant keeping hobby, especially in the United States.

In Virginia, Aphaenogaster rudis is by far the most widespread species, ranging from the coast all the way to the Appalachians. It nests under stones, in wood, and in soil. It may create small mounds but their nests are usually inconspicuous. Colonies do not grow huge, reaching maturity at around 500 workers. This species flies in the morning in late June to early July. Flights start at around 5:15 AM and end around 15 minutes later. The queens and males are attracted to blacklights.

An undescribed species currently under the name "rudis", this species is quite distinct and favors rocky bluff areas. I have only found this species a couple times in Virginia but the colony structure appears very similar to N22a. A notable distinction in habitus is the prevalent yellow coloration on the workers and queens but no obvious morphological distinction between the two species has been made yet; N22a is also quite variable in coloration, so those inexperienced in Aphaenogaster identification should not jump to a determination of N22b based on solely color.

Aphaenogaster picea is the most cold-tolerant species of Aphaenogaster in eastern North America. In Virginia, they are restricted to high-elevation points on the ridges of the Appalachians. Workers and queens are piceous and can be relatively easily differentiated from A. rudis. Colonies do not grow large, similar to A. rudis. 

Aphaenogaster carolinensis may supposedly be found throughout southern and southeast Virginia and can be differentiated from other species by the very narrow head. They are best differentiated from Aphaenogaster rudis by the missing CAD intron. Inland populations of this species may have a broader head, making it more difficult to differentiate from the common A. rudis, but this species primarily nests in sand (although A. rudis will as well).

This species is also a very dark colored Aphaenogaster. However, they are much rarer in Virginia and are also a xeric species, making it easy to differentiate from A. picea, a high-elevation species. The spines are also very prominent, similar to the large spined A. fulva.

Similar in appearance to other large Aphaenogaster such as A. treatae and A. ashmeadi, this species is easily differentiated from the other two by the lack of an antennal lobe and the inwards pointing notch at the scape of the antennae. This species is relatively locally abundant and is extremely common along parts of the four rivers of Virginia (the Potomac, Rappahanock, York, and James). They often have red-orange abdomens similar to that of A. fulva but are differentiated based on the previously mentioned antennal notch, as well as a larger leg-body ratio and thinner head. This species flies in the afternoon.

Aphaenogaster fulva is a very widespread species and gets relatively large colonies. The largest colony of this species I have collected had 819 workers. Although it is regarded as part of the fulva-rudis-texana complex, it is, in reality, quite different from the other species in the complex. The queens of A. fulva have striations on the mesopleuron whereas other species in the complex have a smooth mesopleuron. The workers have a distinct raised mesonotum that only A. umphreyi shares. There are populations of this species that are polygynous and supposedly inbreeding. I have not recorded such populations in Virginia, however. A. fulva gets slightly larger colonies than other members of the fulva-rudis-texana complex and are most commonly found in or near rotting wood, as opposed to under stones. The easiest way to differentiate this species is the raised mesonotum, which is only shared by A. umphreyi. This species flies in the afternoon.

Not much is known about this species. They have not yet been recorded in Virginia but are possibly present in the state due to their cryptic nature and undercollecting in the Southside (southern Piedmont). They are most similar to A. fulva, yet are completely subterranean, xeric, and pale in coloration. They also share the raised mesonotum in A. fulva.

This species was first recorded in Virginia in 2018 by Dr. K. Ivanov. The coloration of this arenicolous species is supposedly related to the coloration of the sand that they nest in. This is the only species of Aphaenogaster in the East that lacks propodeal spines. It is likely the largest, or at least one of the largest, species of Aphaenogaster in the East. Queens have small spines and this species flies in the morning.

Although not yet officially recorded in Virginia, there are very likely populations of this species in Virginia. It is similar in appearance to A. floridana, but has a shinier exoskeleton and distinctly long, upward pointing propodeal spines.

A. tennesseensis is one of the most populous species in the hardwood forests of Virginia. The queens of this socially parasitic species invade the nests of host species of the fulva-rudis-texana complex and overtake the colony through temporary parasitism. A. tennesseensis get the largest colonies of the genus in Virginia, often hollowing out huge trees. The long spines, bright red color, and hairless head separate this species from all others.

A. mariae is my favorite native species. These arboreal, canopy-dwelling ants are also social parasites, usually of A. fulva, and once the queens have invaded a colony in the same fashion of A. tennesseensis, they migrate up into the treetops where they establish a nest. A. mariae seems to be limited to old-growth hardwood forests where they usually nest in oak. In Virginia, I have found a queen of this species in Pohick Bay and they appear to be relatively common in eastern MD (Delmarva) and along the Potomac. In Virginia, they may be found in much of the southern and western forests of the state. This species is quite slow moving and may be difficult to see on the reticulated bark of the trees that they inhabit. However, the workers and queens are easy to identify, as they are extremely punctate, the part of the gaster where the postpetiole connects have fan-like striations radiating from the postpetiole, and the long spines are backwards facing. 

I am not familiar with this species, but it is said to be similar to A. treatae and A. ashmeadi in appearance but without the lobes. The males of this species have thick propodeal spines, it nests dry areas, and has nest entrances similar to that of A. treatae. It is medium-brown and the Umphrey 1995 paper says that it is usually distinct from all other species in the fulva-rudis-texana complex by the short scapes in comparison to the other species.

Also included in the fulva-rudis-texana complex is A. texana (N21B), N19, and N17.

Aphaenogaster texana is variable in color but is often bright and large. It should not be present east of the Mississippi river. Aphaenogaster N19 is a species found in Missouri by James Trager but is likely present throughout the Mississippi Basin. N17 is similar to picea (N18) in color but has longer scapes on average and is found west of the Appalachian Mountains.

Personal observation, Personal comm. with Joe MacGown, Umphrey 1995, DeMarco 2015, Frye 2012

Antennal lobes present at the base of scape -> 2

Antennal lobes not present at base of scape -> 4

Integument flavous in coloration, lacking propodeal spines (queens have small spines) -> Aphaenogaster floridana Smith

Brownish yellow to black in coloration, propodeal spines present -> 3

Lobes taking up 1/4 or more of the total length of scape, gaster generally shining, very large species -> Aphaenogaster treatae Forel

Lobes taking up 1/5 or less of the total length of scape, gaster generally not as shining, very large species -> Aphaenogaster ashmeadi Forel

Mesonotum distinctly raised, propodeal spines generally large and directed upwards, with pilosity throughout body, never piceous -> 5

Not with all of the above characteristics -> 6

Eyes larger, darker in coloration, common species -> Aphaenogaster fulva Roger

Eyes tiny, yellow in coloration, rare subterranean arenicolous species rarely recorded, with distinct sculpture on head -> Aphaenogaster umphreyi Deyrup & Davis

Propodeal spines long and directed backwards, reddish in coloration, generally associated with hardwood trees, queens microgynous, temporary parasitic species -> 7

Not with the above characteristics -> 8

Head and mesosoma lacking most pilosity, not heavily sculptured, lacking wave of striae at base of postpetiole, propodeal spines slightly curved, very common species -> Aphaenogaster tennesseensis Mayr

Head and mesosoma pilose, many rugae sculpturing head and mesosoma, wave of striae directing outwards to gaster from base of postpetiole, propodeal spines directed backwards and straight, arboreal, workers slow and meandering, flights occurring at night -> Aphaenogaster mariae Forel

Flavous in coloration, sand-nesting xeric species -> 9

Not entirely flavous in coloration, or more likely with none at all -> 10

Lacking postpetiolar spines -> Aphaenogaster floridana Smith

Prominent postpetiolar spines -> Aphaenogaster flemingi Smith

Large reddish species with a notched scape -> Aphaenogaster lamellidens Mayr

Not with above characteristics -> 11

Piceous in coloration -> 12

Not piceous in coloration -> Aphaenogaster rudis Enzmann, Aphaenogaster carolinensis Wheeler, Aphaenogaster N22b, and Aphaenogaster N16 left; A. N16 with shorter scapes, other species difficult to separate without DNA analysis, although habitus, location, and habitat can be used to differentiate

Xeric species with large, upwards-pointing propodeal spines -> Aphaenogaster miamiana Wheeler

High altitude species with smaller propodeal spines -> Aphaenogaster picea Wheeler