Canthon Hoffmannsegg, 1817

Edmonds, W. D., 2018, The dung beetle fauna of the Big Bend region of Texas (Coleoptera: Scarabaeidae: Scarabaeinae), Insecta Mundi 642, pp. 1-30 : 5

Canthon Hoffmannsegg

The genus Canthon includes over 200 species restricted to the New World, most of which inhabit tropical South and Middle America. The United States is home to 18 species, of which 16 occur in Texas. Canthon species are the “tumblebugs” universally familiar to naturalists, ranchers, farmers and others who have observed their remarkable habit or fashioning and rolling a ball of dung across the ground and ultimately burying it at some distance from the source. The Big Bend fauna includes four species, all widespread and closely associated with livestock and other grazing mammals, where they can be observed in large numbers jostling for position at a fresh dung pad ( Fig. 3 ). All are dark colored, with evenly rounded bodies lacking any horns or other projections, and long, slender middle and hind legs. While they superficially closely resemble each other, the sexes can be distinguished by a combination of two external attributes: in the male, the protibial spur is bifurcate (usually asymmetrically so) and the last abdominal sternum is emarginate medially to receive the apex of the pygidium ( Fig. 27 ); in the female, the protibial spur is acute (rounded in worn individuals) and the last abdominal sternum is not obviously emarginated medially ( Fig. 28 ). The four Big Bend Canthon species are easily separated by the following key.

1. Clypeus bidentate medially ( Fig. 26, 29 ). Larger beetles, length 10–20 mm .................................................................. [Subgenus Canthon s. str.] 2

— Clypeus quadridentate, middle two teeth larger than outer ones ( Fig. 33–34 ). Small beetles, length ≤ 8 mm ............................................ [Subgenus Boreocanthon ] 3

2. Black, only rarely with hint of blue reflections ( Fig. 29–30 ). Propleuron divided by sharp, transverse carina extending from lateral margin to coxa ( Fig. 31 , arrow).............................................................. Canthon (C.) blumei Halffter and Halffter

— Near black but almost always with blue reflections under strong light ( Fig. 26 ). Propleuron not divided by a carina, smooth and continuous ( Fig. 32 )..... Canthon (C.) imitator Brown

3. Pronotum punctate. Smaller, length 3–5 mm ............. Canthon (B.) mixtus Robinson — Pronotum granulate. Larger, length 5–8 mm ........... Canthon (B.) praticola LeConte

Figures

Figures 1–6. Big Bend maps and dung beetles. 1–3) Location of study area and collection sites. 1) Extension of the Chihuahuan Desert (dark green) in north-central Mexico and southwestern United States. 2) [A] Trans-Pecos Texas showing counties and Big Bend region (shaded); [B] Tri-county Big Bend region (numbers indicate primary collection sites described in Materials and Methods; dots mark secondary sites). 3–6) Beetles in natural settings. 3) Aggregation of Canthon imitator, C. praticola and C. mixtus at cow dung. 4) Canthon imitator rolling ball of cow dung. 5) Stick nest of Neotoma micropus at base of mesquite brush, potential habitat for inquilinous Onthophagus. 6) Canthon blumei feeding directly from javelina carcass.

Figures 26–35. Canthon. 26) C. imitator, dorsal view, male. 27) Same, ventral view of abdomen. 28) Same, ventral view of female abdomen. 29) C. blumei, dorsal view, female. 30) Same, oblique dorsal view of forebody. 31) Same, ventral view of right propleuron (arrow marks transverse carina). 32) C. imitator, ventral view of right propleuron. 33) C. mixtus, dorsal view, male. 34) C. praticola, dorsal view, female. 35) Same, oblique view.