The two most widespread members, Scarites subterraneus and S. vicinus, are shiny black ground beetles with large mandibles, head with two large depressions, elytra grooved and separated from a smooth pronotum by a narrow "waist" (peduncle). Besides differences in antennomere shape as noted in the taxonomic key below, these two species can usually be distinguished by size: most subterraneus body length < 20 mm and elytron < 10 mm compared to most vicinus body length > 20 mm and elytron > 10 mm. Elytron length is the more reliable separator. Earlier reported distinctions based on various external morphologies (protibial denticles, mandibles, body proportions) are unstable and therefore unreliable. Assessment of antennomere shape is unfortunately not reliable in most BugGuide photographs which usually do not capture the required perpendicular viewing angle of the broad faces of the antennomeres. An oblique angle will make the antennomeres appear artificially more elongated.
Distinguishing sex externally in Scarites is difficult as the protarsi appear the same in both sexes. Lindroth (1961) observed that in S. subterraneus the females show four setae-bearing punctures equally spaced along posterior border of last sternite while in males the two median punctures are somewhat more widely spaced. More reliable sex separators follow.
In either sex of Scarites it is rare to observe in curated specimens a naturally exposed apical portion of the genitalia protruding from the abdominal posterior end. However, for many other curated carabid groups the genitalia are frequently exposed which in the female appear as a symmetrical pair of small dark styli while in the male a single median lobe bears to its anatomic left.
When genitalia remain deeply hidden the sex can still be determined by gently probing for the morphologic details of opposing plate structures. In either sex these sets of plates occur just inside the apical openings of relaxed abdomens. The ventral pair of plates are the "genital sternites" and the single dorsal plate is the "genital tergite". In females the pair of genital sternites are split symmetrically down the middle with the adjacent apices right angled. The female genital tergite is thick and darkly scleritized. The male genital sternite set is asymmetrically split with well-rounded apices (left most rounded) and with the left plate somewhat overlapping beneath the right plate. The male genital tergite is thin and pale.
Other ground beetle genera show similar sexual differences in apically exposed genitalia, genital sternite, and genital tergite.
KEY TO NORTH AMERICAN (NORTH OF MEXICO) SPECIES OF SCARITES - version 2014.XII.11a.
The following is a key after Bousquet & Skelley (2010) and Nichols (1986) with consolidations/modifications/expansions by Peter W. Messer. This provisonal taxonomy of North American Scarites awaits refinement from future morphological scrutiny and DNA sequence analysis. Users of this key will find that it supersedes outdated popular keys by Downie & Arnett (1996) and Ciegler (2000).
The most challenging species separation is between S. quadriceps and recently resurrected S. vicinus in the quadriceps group. Body size and relative lengths of metasterna as specified in the key are currently the only reliable ways to externally distinguish the latter two species. Nothing has been published on genitalia comparison. Easy and reliable methods to determine sex externally (as started above) will hopefully encourage investigators to begin serious comparative work on the genitalia in this group.
Because antennomeres are not cylindrical, couplet #1 below requires that the examiner turn each antennomere until its maximal width comes into view. Routine photographs of entire beetles usually do not capture the viewing angle desired for assessing antennomere shape.
Abbreviations: ABL = apparent body length (mandible tip to elytron apex); LE = elytron length; LMs/LMc = ratio of metasternum length to metacoxa length through same line as defined by Bousquet.
1. Antennomeres 8–10 longer than wide (length/width of 10th antennomere = 1.1–1.3) with segments 5–7 usually more elongated. ABL at least 20 mm (LE at least 10 mm) but with a small variant in regions west of Mississippi River ==> 2 [quadriceps group]
– Antennomeres 8–10 wider than long or subquadrate (length/width of 10th antennomere = 0.8–1.0), without obvious further elongation of segments 5–7 (moniliform). ABL ≤ 20.5 mm (LE ≤ 10 mm) ==> 4 [subterraneus group]
–– QUADRICEPS GROUP ––
2. Metasternum visibly same length compared to that of metacoxa (LMs/LMc = 0.98–1.02) and nearly same length compared to that of mesocoxa. ABL 20.5 mm - 26.0 mm. LE 10 - 13.0 mm. Common and widespread throughout North America in which many northern specimens are mislabeled "S. quadriceps". Bousquet (2012): AL, AR, IA, IL, IN, KS, KY, LA, MN, MO, MS, ND, NE, OH, OK, ON, TN, TX, WI. ==> S. vicinus Chaudoir
– Metasternum proportionally longer compared to metacoxa (LMs / LMc = 1.10–1.30) and clearly much longer than mesocoxa. ABL > 27.0 mm OR ABL ≤ 20.5 mm ==> 3
3. ABL > 27.0 mm. LE at least 14.0 mm. Uncommon in north-central USA with somewhat increasing occurrences southward and eastward from Kansas to the Atlantic and Gulf Coast states. Bousquet (2012): AL, FL, GA, LA, MD, MS, NC, NJ, SC, TX. ==> S. quadriceps Chaudoir
– ABL ≤ 20.5 mm. LE < 11.0 mm. West of the Mississippi River (KS, LA, NM, OK, TX). Elytra with intervals flat and striae often less impressed laterally ==> S. lissopterus Chaudoir sensu Nichols (1986).
–– SUBTERRANEUS GROUP ––
4. Setigerous puncture present on proximal elytral interval #3. Elytral striae impunctate. Metasternum proportionally more elongate (LMs / LMc = 1.10–1.40). Membranous wings fully developed. Widely distributed in the United States and also in southern Ontario ==> S. subterraneus Fabricius [synonyms include S. texanus (small Texan variant with weakly impressed striae), S. californicus (CA), and S. patruelis (FL, GA)]
– Setigerous puncture on proximal elytral interval #3 absent (or present in some S. ocalensis). Metasternum proportionally shorter (LMs/LMc = 0.75–1.03). Membranous wings reduced. Range only LA to FL in North America ==> 5
5. Eyes flat, head width at level of eyes smaller than at level of temples. Pustules at base of elytra more expanded, reaching level of humeral carina apex between intervals 2–4. Elytral interval 7 markedly convex, more or less cariniform, in basal third. Elytral striae impunctate. Known only from sandy soil in Levy Co, FL ==> S. stenops Bousquet & Skelley
– Eyes slightly to moderately convex, head width at level of eyes subequal or greater than width at level of temples. Pustules at base of elytra less expanded, distinctly not reaching level of humeral carina apex between intervals 2–4. Elytral interval #7 slightly convex or flat in basal third ==> 6
6. Elytral striae very finely impressed, vanishing at apex, striae with punctulae. Elytra very shiny (disc without microsculpture). Metasternum proportionally more elongate (LMs / LMc = 0.98–1.03). Eyes more convex, head width at level of eyes greater than width at level of temples. Larger body size (usually LE > 7.5 mm). Occurs on sea beaches of FL and LA Gulf Coast ==> S. marinus Nichols
– Elytra with striae well impressed without punctulae, with distinct microsculpture. Metasternum proportionally shorter (LMs/LMc = 0.76–0.84). Eyes less convex, head width at level of eyes subequal to width at level of temples. Small body size (elytron < 7.5 mm). Known only from peninsular FL (inland and coastal) ==> S. ocalensis Nichols
The seven valid North American species of Scarites including some synonyms according to the catalogue by Bousquet (2012)(4)
S. lissopterus Chaudoir, 1880: p93 - considered a synonym of S. quadriceps earlier by Bousquet & Skelly (2010)
S. marinus Nichols, 1986
S. ocalensis Nichols, 1986
S. quadriceps Chaudoir, 1843: p729 [syn. S. substriatus Haldeman]
S. stenops Bousquet & Skelley, 2010
S. subterraneus Fabricius, 1775 [syn. S. californicus LeConte, S. patruelis LeConte, S. texanus Chaudoir, 1880: p94]
S. vicinus Chaudoir, 1843
Chaudoir, M. de. 1843. Bulletin de la Société impériale des naturalistes de Moscou 23.
Chaudoir, M. de. 1880. Annales de la Societe Entomologique de Belgique 23: 5-130.
Lindroth, C.H. 1961. Opuscula Entomologica, Supplementum 20.
Nichols, S.W. 1986. Proc. Entomol. Soc. Wash 88(2): 257-264.
Bousquet, Y., and P.E. Skelley. 2010. The Coleopterists Bulletin 64(1): 45-49.
Ontario and most of United States except northwestern states. Also represented in Mexico, Cuba, Eurasia, India, Madagascar, others?
For historical taxonomic interest, below are the seven species names and their associated ranges as they appeared in a catalogue by Bousquet & Larochelle (1993):
S. lissopterus - KS, NM, OK, TX
S. marinus - FL to LA
S. ocalensis - FL only
S. patruelis - GA, FL
S. quadriceps - eastern US plus Ontario: NJ to FL to TX to SD to ON
S. subterraneus - Ontario and most of US except northwestern states
S. texanus - TX [SC]