Key to queens of Nearctic Tapinoma

Key to the queens of Tapinoma species occurring in the Nearctic region north of Mexico, based on Cover & Rabeling (2024).

1

Maxillary palp segments 2–4 strikingly flattened and notably broader than palp segments 1, 5, and 6. Labial palp segments 2 and 3 also flattened. Workers distinctly bi-colored with dark, almost black head and mesosoma contrasting sharply with pale yellow-white metasoma and appendages. [pantropical tramp, heated greenhouses, and buildings, outdoors in southern Florida, exotic] => Tapinoma melanocephalum
Maxillary and labial palp segments subcylindrical, not strikingly flattened and broad. Workers (if present) often uniformly colored; if bicolored, different from pattern described above => 2

At least some erect hairs present on gastric tergites 1–3, sometimes short erect hairs present on mesosomal dorsum as well. Pubescence on antennal scapes short but suberect => 3
Erect hairs absent on mesosomal dorsum and gastric tergites 1–3. Pubescence on antennal scapes variable but generally appressed => 4

Short erect hairs present on mesosomal dorsum and gastric tergites 1–3. Antennal scapes long, projecting well beyond the posterior corners of the head, and reaching maximum diameter between the antennal insertion and the midpoint. Short but dense suberect pubescence present on scapes and most dorsal body surfaces. Palp formula (5,4). (Fig. 2) => Tapinoma inflatiscapus

Cover & Rabeling (2024), Figure 2. Morphological comparison of the Tapinoma inflatiscapus holotype queen A, E and a paratype male B, F in lateral A, B and full-face E, F view. For the dorsal views of T. inflatiscapus C, D dealate queen C and male D paratypes were photographed. The type series was collected at Cove Mountain in Utah and belongs to a single nest series with the collection code SPC 7816. Scale bar: 0.5 mm (A–F).

Erect hairs absent on mesosomal dorsum. Antennal scapes short, barely, or just reaching the posterior corners of the head, subcylindrical, tapering in diameter only near the antennal insertion and near the apex. Palp formula (6,4). [subtropical Florida, the Caribbean region, arboreal] => Tapinoma litorale

In full-face view, head trapezoidal, broadest near the posterior border well behind the large compound eyes, sides straight or slightly convex (except for the broadly rounded posterior corners), and strongly converging anteriorly. In lateral view, dorsal petiolar scale absent. In dorsal view, anterodorsal margin of petiole convex; petiole broadest at midpoint => 5
In full-face view, head shape variable, either subrectangular or sides of head convex with head widest at level of eyes. In lateral view, petiolar scale either absent or forming a small, rounded node. When small node present, shape of petiole when viewed from the rear trapezoidal or subrectangular, dorsal margin slightly convex to flat or concave. If petiolar scale absent, head widest at level of eyes in full-face view => 6

Queen bicolored with head and mesosoma orange to dull red, often with patches of darker infuscation, forming a strong contrast with the uniformly black or brown gaster. Note: workers combining the following: head and mesosoma orange to red, metasoma brown to black; in full-face view, posterior margin of head concave. [mountains of southern Nevada, and central to southern California] => Tapinoma schreiberi
Queen usually uniform gray or brownish gray, variable in size. Note: workers uniform gray to yellowish brown, sometimes weakly bicolored, but never as described above; in full-face view, posterior margin of head usually straight or weakly convex, rarely slightly concave. [omnipresent from sub-boreal Canada south through the Mexican highlands]. (Fig. 5) => Tapinoma sessile

Cover & Rabeling (2024), Figure 5. Morphological comparison of a Tapinoma sessile queen A, C, E and a male B, D, F in lateral A, B, dorsal C, D, and full-face E, F view. Individuals were collected in the Black Forest in Colorado and belong to a single nest series with the collection code SPC 4118. Scale bar: 0.5 mm (A–F).

In lateral view, petiolar scale absent. In lateral view, propodeum forming a single, flat declivitous surface. Palp formula (5,4). (Fig. 4) => Tapinoma shattucki

Cover & Rabeling (2024), Figure 4. Morphological comparison of the Tapinoma shattucki holotype queen A, E and a paratype male B, D, F in lateral A, B dorsal D and full-face E, F view. For the dorsal view of the T. shattucki queen C, a dealate paratype was photographed. The type series was collected in Stow, Massachusetts and belongs to a single nest series with the collection code SPC 7633. Scale bar: 0.5 mm (A–F).

In lateral view, petiole with a small dorsal rounded node. In lateral view, propodeum with dorsal and posterior surfaces that meet to form a convexity. Palp formula either (4,3) or (5,4) => 7

Palp formula (5,4). Shape of petiole when viewed from the rear subrectangular, dorsal margin slightly convex to flat. In side view, propodeum subangulate with dorsal face notably shorter than posterior face; posterior face slightly concave. Anterior clypeal margin flat. (Fig. 3) => Tapinoma pulchellum

Cover & Rabeling (2024), Figure 3. Morphological comparison of the Tapinoma pulchellum holotype queen A, C, E and a paratype male B, D, F in lateral A, B dorsal C, D and full-face E, F view. The type series was collected in two adjacent pitfall traps at Eno River State Park in North Carolina. Scale bars 0.5 mm (A, C–E); 0.25 mm (B, F).

Palp formula (4,3). Shape of petiole when viewed from the rear trapezoidal, broadest at apex, dorsal margin concave, rarely flat. In side view, propodeum broadly rounded, forming an even convexity. Anterior clypeal margin with small median impression. (Fig. 1) => Tapinoma incognitum

Cover & Rabeling (2024), Figure 1. Morphological comparison of the Tapinoma incognitum holotype queen A, C, E and a paratype male B, D, F in lateral A, B dorsal C, D and full-face E, F view. The type series was collected in Alumbed Hollow in Utah and belongs to a single nest series with the collection code SPC 7749. Scale bars: 0.5 mm (A–D); 0.2 mm (E, F).