Trachymyrmex ruthae, Neal A. Weber, University of North Dakota, 1936

Neal A. Weber, University of North Dakota, 1936, The biology of the fungus-growing ants. Part. I. New forms. 1, Revista de Entomologia 7, pp. 378-409 : 402-404

Trachymyrmex ruthae , sp. nov.

Worker: Length 4-5 mm. - Head, excluding mandibles, as broad as long. Medial impression of posterior margin broad, rounded, and passing over dorsal surface of head to frontal area in a rounded groove whose margin are slightly carinate and further delimited by setigerous tubercles. Occipital corners without spines, bisected by a rounded groove and bordered by setigerous tubercles. Sides of head beneath occipital corners tubercu!ate. Eyes moderately convex, situated dorso-laterally at a distance from the mandibular insertions slightly less than the diameter of the eyes. Antennal scrobes complete except dorso-medially. Clypeus projecting in a lobe which is broadly notched medially. Mandibles with large apical tooth, subapical tooth less than half the size of the apical tooth, and 5-6 much smaller teeth along the cutting border. Antennal scapes exceeding occipital angles by a distance slightly less than their distal diameters. Terminal joint of funiculus slightly shorter than joints 7-9 taken together and slightly longer than joints 2-4 taken together.

Thorax with compressed, spatulate inferior pronotal spine and stout and acute lateral pronotal spine which is largest spine of body, distinctly larger than epinotal spine. Between these spines the pronotum is in some workers transversely carinate and bears 5-8 irregular, acute, and setigerous tubercles. Mesonotum surmounted by a disk bearing on its rim irregular tubercles, in this resembling Mycocepurus . The most posterior lateral tubercle, viewed from the side, is generally in the form of an irregularly bituberclate spine. Mesoepinotal impression deep and rounded. Basal surface of epinotum not distinctly carinate laterally but bearing here a series of irregular tubercles. Epinotal spine large, stout, and acute.

Anterior and posterior surfaces of petiole, viewed laterally, plane. Anterior face of postpetiole nearly vertical and at right angles to dorsal or posterior surface, the latter irregularly tuberculate. Viewed from above the postpetiole is twice as broad as the petiole and is broadly impressed postero-medially. - Gaster not distinctly impressed medially but coarsely marginate on sides; coarsely tuberculate. Legs moderately long and stout.

Opaque, finely shagreened; dorsal surfaces of gaster coarsely reticulate. Prosternites are covered with a silvery bloom. - Tubercles of body bearing reclinate to upright hairs, appearing black basally, gray distally. Aside from pubescence on funiculi and tarsi the body is otherwise free from pilosity. - Dark ferruginous, gaster brown.

Female: Length 5.5-6.5 mm. - Head broadly impressed on posterior margin and with impression carried over head to median ocellus as a smooth, shallow groove, bordered laterally by tuberculate carinae. Lacking occipital spine as in the worker. Antennal scapes exceeding occipital corners by a distance equal to less than their distal diameter. Lateral pronotal spines low but stout. Mesonotal scutum densely and finely tuberculate. Epinotal spines large and stout. Integument and pilosity as in the worker. Brown, appendages lighter.

Male: Length 3.8-4.4 mm. - Head, excluding mandibles. 0.9 as long as broad between external margins of eyes. Eyes convex, greater in diameter than the distance from them to the lateral ocelli. Clypeus deeply notched. Antennal scapes long and but slightly bent distally. Terminal joint of funiculus longer than joints 2-5 taken together or joints 10-11 taken together. Pronotum,with distinct lateral tubercles in place of lateral spines in the female. Scutum of mesonotum high, convex, and overshadowing pronotum. Epinotum convex, with a slight angularity in place of spines. Postpetiole, in profile, rounded above, 0.8 as high as postpetiole. Gaster ovate. Legs long and slender. Surface of body finely reticulate. Mayrian furrow distinct, transversely crossed on anterior arms by short carinulae. Hairs very sparse, short and curved. Dark brown, mandibles and appendages lighter. Median and parapsidal light brown streaks on the scutum.

Described from all castes of a colony taken by myself July 24, 1935, in the foothills north of Tunapuna, Trinidad, B. W. I.

The entrance to the nest was in the form of a circle of twigs loosely adhering together. This led by three tunnels, first to the original small chamber 4.5 cm. in diameter x 2.5 cm. high and thence to a deeper and larger chamber 2 x 11 x 5 cm. high, the latter containing the fungus garden which was partly pendant, partly sessile. Photographs and fuller descriptions of the nest and the biology of this species will be given in a subsequent paper.

In close proximity and, in fact, surrounding this nest were nests of Apterostigma urichi , Apterostigma sp., Cyphomyrmex rimosus subsp . and Pheidole sp., together with a dealate female Pheidole and a dealate female of Apterostigma .

This is a very distinct species quite unlike any known to me.