Onthophagus knausi Brown, 1927

Edmonds, W. D., 2018, The dung beetle fauna of the Big Bend region of Texas (Coleoptera: Scarabaeidae: Scarabaeinae), Insecta Mundi 642, pp. 1-30 : 11

Onthophagus knausi Brown

Fig. 49–53

Diagnosis. Dull black, occasional reddish-brown highlights on head. Small, length 2–5 mm. Pronotum densely punctate, punctures flat, annular, often with central seta ( Fig. 53 ), more crowded anteriorly and laterally; elytral interstriae each with irregular row(s) of small, setose tubercles; apex of pygidium distinctly shinier, more convex and coarsely punctate apically than basally. Male ( Fig. 49 ) – Clypeal carina absent, frontal carina absent except in smallest individuals; clypeal margin reflexed upward, truncate to broadly bidentate; front legs ( Fig. 52A ) slender, elongate, apex of femur extending beyond lateral pronotal margin, tibia narrowed, elongate, apical third noticeably curved inward, apex (above spur) with pencil of yellow hairs; anterior margin of pronotum produced as triangular (sometimes tablike) protuberance overhanging anterior margin ( Fig. 49 ). Female ( Fig. 51 ) – Clypeal carina present, usually sharp and broadly curved anteriorly, frontal carina present, thickened and raised medially; clypeus bidentate, not upturned medially; front legs ( Fig. 52B ) not elongate, femora not extending beyond pronotal margin, tibia evenly bowed, apical third not abruptly curved inward, lacking hair pencil; pronotum evenly convex, only rarely with slightest hint of anteromedian protuberance. This species is described by Howden and Cartwright (1963).

Big Bend collection sites (altitudinal range: 1475–1555 m [2490 m in Sierra El Carmen]).

Brewster Co.: [1] ~ 17 km W Alpine ( Paisano Baptist Encampment ), 30°17′37″N 103°47′35″W, 1550 m (Jul) .

Jeff Davis Co: [1] Davis Mountains Preserve , 31°41′40″N 104°07′30″W, 1850 m (Jul–Aug) ; [2] ~ 16 km NE Valentine, Muerto Springs Ranch (Muerto Springs), 30°40′50″N 104°20′22″W, 1555 m (Jul–Aug) ; [3] ~ 8 km SE Fort Davis (via TX 118 ), Chihuahuan Desert Research Institute (Quarry Unit), 30°32′06″N 103°50′37″W, 1480 m (Aug) .

Presidio Co.: [1] Pinto Canyon Ranch (~ 58 km SSW Marfa on FM 2810), 30°01′18″N 104°27′42″W (headquarters area), 1475 m (Aug).

MEXICO: Coahuila, Sierra El Carmen, 28°59′30″N 102°32′54″W, 28°59′54″N 102°36′42″W, 29°00′06″ N 102°35′48″ W, 1815–2490 m (Jul) .

Collection method(s). a) baited pitfall trap (human feces).

Habitat. Montane and grassland riparian corridors.

Surface activity. Unknown.

Comments. My identification of Big Bend populations as O. knausi was provisionally corroborated by the late Henry F. Howden (pers. comm.). However, definitive identification of Big Bend populations of this species must await a re-examination of the taxonomic status of this as well as a small group of closely related species ( O. mextexus Howden and Cartwright ; O. alluvius Howden and Cartwright and O. knulli Howden and Cartwright ). The type series of O. mextexus (originally described as O. monticolus ) includes a single specimen from Boot Springs, in the Chisos Mountains of Big Bend National Park; the remainder were collected in the Sierra Madre Oriental south of Monterrey, Nuevo Leon, about 500 km SSE of the park. According to details provided by Serge Laplante of the Canadian National Collection in Ottawa, who kindly examined it on my behalf, the Boot Springs specimen is similar to O. knausi from elsewhere in the Big Bend as well as material collected by me in Sierra El Carmen, Coahuila, across the Rio Grande from Big Bend National Park. For now, I regard the Boot Springs specimen as conspecific with other Big Bend populations of O. knausi , and not a putative fifth Big Bend species of Onthophagus .

With an average length of about 4 mm, O. knausi is the smallest of the Big Bend dung beetles. It prefers riparian areas, where it can occur in high numbers. Creekside traps at Pinto Canyon Ranch and the Quarry section of the Chihuahuan Desert Research Institute commonly yielded 100 or more (up to 250) individuals in 48-hour lethal pitfall traps. I never collected it from either cattle or horse droppings. It probably survives on the droppings of deer, javelina and other animals frequenting intermittent creek and streambeds. Ratcliffe and Paulsen (2008) report O. knausi from human feces baited traps in wooded areas of southeastern Nebraska. Onthophagus knausi is a wide-ranging species. Riley and Wolfe (2003) report it from the Trans-Pecos, Edwards Plateau and south Texas plains/lower Rio Grande vegetational areas of the state; it undoubtedly occurs widely to the south of the Rio Grande in adjacent areas of northern Mexico. Howden and Cartwright (1963) report it also from Kansas, Nebraska and Illinois.

Figures

Figures 49–59. Onthophagus and Digitonthophagus. 49) O. knausi, dorsal view, male. 50) Same, dorsal view, female. 51) Same oblique frontal view, female. 52) Same, prolegs (A, male; B) female). 53) Same, pronotal sculpturing. 54) D. gazella, dorsal view, male. 55) Same, partial oblique frontal view of forebody. 56) Same, proleg, male. 57) Same, oblique frontal view of female forebody. 58) Same, dorsal view, female. 59) Same, apex of protibia and protarsus (A, female; B, male [arrow marks apical tibial “digit”]).