New World Temnothorax species groups

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The species groups detailed here are based on Mackay, W. P. 2000. A review of the New World ants of the subgenus Myrafant, (genus Leptothorax) (Hymenoptera: Formicidae). Sociobiology. 36:265-444.

This revision was done before most species of Leptothorax were moved into the genus Temnothorax thus the text has been edited to reflect these changes.

The species in this study were divided into species complexes, although these complexes can be difficult to define. In some cases they are unlikely to represent monophyletic groups. For example, L. oxynodis is considered a member of the nitens species complex, despite being the only member of the group to have an 11-segmented antennae. The other members of the complex all have 12 antennal segments. Leptothorax oxynodis may be a member of a complex with an 11-segmented antenna but does not seem to belong to any of these groups. The nitens complex and andrei group may be polyphyletic groups, as both are united primarily by similarities in their petioles. Other species complexes appear to be well defined, such as the emmae complex, hispidus complex, silvestrii complex (although the 2 members have 11 and 12 segmented antennae), and even the large tricarinatus group, which is based on the form of the clypeal carinae. There are also single species complexes, which include the striatulus complex and the obturator complex. Each of these species are so distinctive they stand apart from all their congeners.

There is a Key to the New World Temnothorax species groups.

Temnothorax andersoni species complex

Members of this species complex can be recognized by the 12-segmented antenna and by the often broadly rounded petiolar node. The postpetiole is occasionally widened, as compared to the petiole. The clypeus has several carinae, with the medial carina being only slightly more prominent than the others. The region next to the medial carina has smaller carinae, and is usually not smooth and shiny. This complex is closely related to the tricarinatus species complex, which has 3 major carinae on the clypeus, including a sharp, well-defined medial carina and two lateral carinae, which converge anteriorly (specifically T. carinatus, T. cokendolpheri, T. gallae and T. rugulosus).

Key to Temnothorax andersoni species group workers

Temnothorax andrei species complex

Members of this species complex can be recognized as the medial clypeal carina is poorly developed, the lateral carinae are well developed or several are present. The surface of the clypeus is convex. The antennae has 12 segments. The anterior and posterior faces of the petiole are nearly parallel, and the top of the node is usually rounded or truncate. The subpeduncular process is nearly always small and poorly developed. The propodeal spines are small and usually consist of only feeble angles or small spines. Some of the members of the tricarinatus complex may be confused with members of the andrei-complex: T. bestelmeyeri, T. brevispinosus, T. furunculus, T. mexicanus, T. neomexicanus, and T. punctithorax.

Key to Temnothorax andrei species group workers

Temnothorax emmae species complex

Members of this species complex can be recognized by an 11-segmented antenna, a thickened, blunt, rounded petiolar node, and that the dorsum of the head is partially smooth and shining with fine striae. The suprapeduncular process is well developed, with a curved dorsal surface. These characters, in addition to the 11-segmented antenna, will easily separate this complex from the andersoni complex in which the shape of the node is similar.

The species can be differentiated using the following couplet:

  • Bicolored (head and gaster dark, mesosoma, petiole, and postpetiole red); dorsum of mesosoma with longitudinal striae . . . . . Temnothorax emmae
  • Concolorous dark brown (mesosoma rarely lighter in color); mesosoma without prominent longitudinal striae . . . . . Temnothorax whitfordi

Temnothorax hispidus species complex

Members of this species complex are large (over 3mm total length), and can be recognized by the pedunculate petiole. The node of petiole is broadly rounded or truncate, and thickened as seen in profile. The propodeal spines are small. The eyes are small, the minimum diameter is about 1/2 to 2/3 the distance between the anterior border of the eye and the base of mandible. The head and mesosoma are coarsely sculptured with rugae or coarse striae, the intrarugal spaces are densely and coarsely punctate. This is a Mexican group, with a single species (T. hispidus ) which barely enters the southern United States.

Key to Temnothorax hispidus species group workers

Temnothorax longispinosus species complex

Members of this species complex can be recognized by the 11-segmented antenna, the petiolar node is obliquely truncate and sloping posteriorly, the mesosoma is roughly sculptured in most species, and the head is roughly sculptured in some of the species, smooth and shining in others. The clypeus has a single medial carina and 2 prominent lateral carinae, as well as additional carinae. It could be confused with the tricarinatus complex, but differs in having a 11-segmented antenna.

Key to Temnothorax longispinosus species group workers

Temnothorax nitens species complex

Members of this species complex can be recognized by the sharp apex of the petiolar node and that the propodeal spines are usually poorly developed. The medial clypeal carina is poorly developed and not more prominent than the numerous lateral carinae. Most species have a 12-segmented antenna. Three species in the tricarinatus complex, T. adustus, T. chandleri, and T. coleenae, may be confused with members of this group due to their sharp noded petiole.

Key to Temnothorax nitens species group workers

Temnothorax obturator species complex

The only species in this complex, Temnothorax obturator, can be recognized as the propodeal spines are united by a carina. In addition, the propodeum is depressed when compared to the remainder of the mesosoma.

Temnothorax schaumii species complex

This species complex can be recognized by the 11-segmented antennae, the node of the petiole is convex (occasionally concave) anteriorly and posteriorly (as seen in profile). The node is not broadly rounded as in the emmae complex and the dorsum of the head is nearly completely covered with fine striae.

Key to Temnothorax schaumii species group workers

Temnothorax silvestrii species complex

The silvestrii species complex appears to be the most plesiomorphic in the subgenus, and possesses a number of characteristics that link this subgenus to the Tetramoriini. These characters include a raised area on the lateral surfaces of the clypeus, directly anterior to the insertions of the antennae. It is not as developed as it is in Tetramorium but it is more developed than in other members of the subgenus Myrafant. The maxillary palps have 5 segments, the labial palps have 3 segments, as other members of Leptothorax, which clearly demonstrates the proper placement of T. silvestrii in Leptothorax. Additionally, the mandible has 5 teeth, as in most other Leptothorax. The propodeal spines are long and well developed, whereas they are usually short in the remainder of the subgenus. The node of the petiole is quadrate or subquadrate as in Tetramorium not rounded or with a sharp apex in most of the species of Myrafant. These ants are larger than is typical for Myrafant and are coarsely sculptured with rugae, characters it shares with Tetramorium. Although T. silvestrii was once considered a member of Tetramorium it is clearly a Leptothorax, especially when one considers the closely related T. smithi. This complex includes T. silvestrii and T. smithi, which can be easily separated as T. silvestrii is from Arizona, has a 12-segmented antenna, and has roughened sculpture on the dorsum of the gaster whereas T. smithi is found in eastern US, has an 11-segmented antenna, and has a smooth and glossy gastral surface. Leptothorax rugosus, a member of the nitens complex, may be related as it also has the incrassate femur with a weakly sculptured gaster. It can be separated from the other two by the sharp petiolar apex.

Temnothorax striatulus species complex

Temnothorax striatulus, the only species in this complex, can be recognized as it lacks spines or even angles on the propodeum.

Temnothorax tricarinatus species complex

This species complex can be recognized by the 3 prominent carinae on the clypeus (1 medial and 2 lateral). The lateral carinae on the clypeus somewhat converge anteriorly. The area between the medial carina and the lateral carinae is usually smooth and glossy. There are usually additional finer carinae on the clypeus. Many species often have a widened postpetiole, as compared to width of petiole. In addition, the 12-segmented antenna has a relatively short scape, which fails to reach the occipital corner by at least one diameter, and the mesosoma is without a mesopropodeal constriction. This complex is closely related to the andersoni complex, but can be separated by the 3 prominent carinae on the clypeus. Specimens with weakly developed carinae will probably be members of the andersoni species complex.

Key to Temnothorax tricarinatus species group workers