Dacetonini, Myrmicinae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
| Key to Costa Rican species of Strumigenys | Species List |
The dacetonines are a diverse lineage found throughout the world. Many species are known to be strictly predaceous, and all are assumed to be. Most of them have highly modified mandibles relative to the standard triangular mandible common to most other ants. Many have mandibles that are elongate, linear, and with opposing tines at the tip (convergent with other lineages such as Odontomachus in the Ponerinae). Others have elongate mandibles like serrated scissors. Others have serrated mandibles that curve ventrally. Most dacetonines are slow-moving, small, and very cryptic. Most are found in or under rotten wood, and in the leaf litter. Dacetonines are difficult to locate by visual search, but litter sifting followed by extraction in Winkler bags or Berlese funnels often yields abundant material.
The dacetonine genera currently known for Costa Rica are Acanthognathus, Glamyromyrmex, Neostruma, Smithistruma, Strumigenys, and Trichoscapa. I avoid giving details of generic definitions here, because Barry Bolton of the British Museum is currently revising "smithistrumiform" dacetonines, and the generic definitions will change dramatically.
Key to Costa Rican Strumigenys (first couplet)
This key relies almost entirely on the key in Brown (1962). The figures below illustrate the habitus of Strumigenys, and some of the main characters used in species-level identifications. Measurements are:
HL: head length; maximum length of head as seen from dorsal full-face view, including all of clypeus and vertex lobes, but not mandibles.
HW: head width; maximum width of head in same view as HL.
ML: mandible length; exposed length of mandibles, including apical teeth, measured in same view from which HL is obtained.
CI: cephalic index; 100xHW/HL.
MI: mandibulo-cephalic index; 100xML/HL.
1a. Apical fork of mandible without distinct intercalary teeth or denticles (intercalary teeth can be difficult to see; select specimen in which the tips of the mandibles are somewhat separated and tilt specimen to anterior view of mandibles; backlighting often helps) : 10
1b. Apical fork of mandible with one or more intercalary denticles (several common species have the apical fork relatively small, with two tiny intercalary denticles that are difficult to see; often the mandibles are closed on specimens, and the intercalary denticles impossible to see): 500
10a. Mandible without preapical teeth or denticles: 20
10b. Mandible with 1 or 2 preapical teeth and/or denticles: 250
20a. Postpetiole large and convex, its dorsum smooth and shining; setae on gaster straight; larger, more robust species: consanii
20b. Postpetiole small, its dorsum densely punctulate and opaque; setae on gaster flagelliform, bent, coachwhip-like; smaller, more slender species: 100
100a. Setae on dorsum of gaster relatively shorter, stouter; propodeal spines relatively larger: pariensis
100b. Setae on dorsum of gaster relatively longer, thinner; propodeal spines relatively smaller: elongata
250a. First segment of gaster margined for its full length on each side by a strong, raised dorsolateral ridge: marginiventris
250b. First gastral segment smoothly rounded dorsolaterally, without raised margins apart from the basal costulae: 370
370a. Head with a strong concavity anterior to each eye, and thus appearing constricted in full-face view; humeral tubercles large and produced: precava (keys twice due to variability in intercalary teeth)
370b. Head parallel-sided or gently tapered in front of eyes; humeral tubercles or angles small, not produced: 375
375b. Smaller species with mandibles not so long; combined length of head + mandibles < 1.10mm: 438
438a. Compound eye anteriorly detached, i.e., bounded in front by a narrow cleft or notch in the ventrolateral margin of the head: rogeri
438b. No preocular notch in ventrolateral border of head: 445
445a. Erect setae on gastral dorsum spatulate: calamita or nastata
445b. Erect setae on gastral dorsum filiform: perdita or nastata
500a. Apical fork of mandible with a single intercalary tooth or denticle, either separate or occurring as a spur on the inner side of the ventral tooth: 510
500b. Apical fork of mandible with 2 intercalary denticles: 750
510a. Mandible with no preapical teeth, or with a single preapical tooth or denticle, or with a preapical tooth or denticle plus another minute denticle proximal to it: 520
510b. Mandible with 2 well-developed preapical teeth: 635
520a. Mandible without preapical teeth or denticles: 530
520b. Mandible with a preapical tooth or denticle, or both: 570
530a. Petiole claviform, the node only feebly differentiated from its anterior peduncle; gastral hairs mostly stiff, spatulate: ludia
530b. Petiolar node with a distinct anterior face, set off from its anterior peduncle; gastral hairs either stiff but filiform, or long, finely flagelliform, coachwhip-like: 554
554a. Erect gastral hairs stiff, filiform, not coachwhip-like; head relatively wider (CI 82): sevesta
554b. Erect gastral hairs long, finely flagelliform, coachwhip-like; head relatively narrower (CI 71-74): 560
560a. Pronotal dorsum finely reticulate-punctate, usually without any costulate sculpture; but if a few faint costulae occur they are insignificant and obviously secondary to the reticulate-punctate component: micretes (keys twice due to variability in preapical denticles).
560b. Longitudinal or oblique costulation as the main component on the pronotal dorsum; any punctate sculpture that may be present is feeble and very obviously secondary to the costulate component: humata
570a. Face strongly flattened, largely concave, margined laterally by frontal carinae: platyscapa
570b. Face convex: 578
578a. Ventral ends of propodeal lamellae at most rounded or bluntly angulate, not dentiform: 580
578b. Propodeal teeth large and acute, matched on each side below by a metasternal tooth of nearly the same size and shape arising from the ventral end of the infradental lamella: trinidadensis (keys twice due to variability in preapical denticles)
580a. Long fine flagelliform hairs on nodes of petiole and postpetiole and on gastral dorsum very numerous, too many to count: 584
580b. Hairs of nodes and gastral dorsum much fewer, at most about 34 on gastral dorsum, long flagelliform or stiff: 600
584a. Eye with approximately 20 facets; costae of gaster fine, numerous, variable in extent, from basal 1/4 or less to covering entire surface of first gastral tergum: lanuginosa
584b. Eye with fewer than 10 facets; costae of gaster coarse, few, restricted to basal 1/4 or less, rest of gaster smooth and shining: cosmostela
600a. Head with a strong concavity anterior to each eye, and thus appearing constricted in full-face view; humeral tubercles large and produced: precava (keys twice due to variability in intercalary teeth)
600b. Head parallel-sided or gently tapered in front of eyes; humeral tubercles or angles small, not produced: 603
603a. Gaster mat, with stiff, clavate setae: idiogenes
603b. Gaster shiny, usually with thin, flagelliform setae: 605
605a. Smaller species, with mandibles < 0.42mm long; head length 0.64mm or less; head broader (CI>75): nevermanni
605b. Larger species, with mandibles 0.42mm or longer; head length 0.69mm or more; head narrower (CI 75 or less): 618
618a. Gastral dorsum with setae stiff, straight, slightly thickened: diaptyxis
618b. Gastral dorsum with setae long, thin, flagelliform: micretes (keys twice due to variability in preapical denticles).
635a. Large species with massive head and short, heavy mandibles (head width > 0.85mm, MI 50 or less): godmani
635b. Smaller species, with more typically proportioned head: 640
640a. Gastral dorsum finely longitudinally striolate, sericeous-opaque, with very abundant, fine, erect flagelliform pilosity: trinidadensis (keys twice due to variability in preapical denticles)
640b. Gastral dorsum with either sculpture or pilosity or both different from the above: 645
645a. Mandibles longer than the head (MI 109-123): 660
645b. Mandibles shorter than head: 697
660a. Specialised humeral hair stiff and freely projecting, approx. straight or nearly so, simple or slightly expanded apically; dorsolateral margin of the head close to the apex of the scrobe with stiff projecting hair present: cordovensis
660b. humeral hair short, broadly spatulate, curved posteriorly and closely applied to the surface; dorsolateral margin of the head without stiff projecting hair: deletrix
697a. Propodeal lamellae without dorsal teeth or angles, ventral angle present and prominent; basal costulae on gaster short to absent, less than 0.05mm long along midline: biolleyi
697b. Propodeal lamellae angulate or toothed both above and below; basal costulae on gaster longer, approximately 0.10mm or longer along midline: 725
725a. First gastral tergum with numerous short, strongly spatulate setae; head narrow (CI 65): borgmeieri
725b. First gastral tergum nearly nude, the few scattered setae long and flagelliform; head broader (CI > 80): smithii
750a. Mandible with a single small preapical tooth; no additional preapical teeth or denticles on inner border: louisianae
750b. Mandible with 2 or more preapical teeth and/or denticles: 875
875a. Mandible with at most 2 preapical teeth and/or denticles: 885
875b. Mandible with 3 or more preapical teeth and/or denticles: 938
885a. Mandible with 1 preapical tooth and a single additional minute denticle near the apical third of the mandibular length; gastral dorsum with abundant, stiff, erect, spatulate hairs; sculpture of gastral dorsum reticulate-striate, opaque: dubitata
885b. Mandible with 2 well-developed preapical teeth; gastral dorsum with at most a few long-flagelliform hairs (although ground pilosity may be abundant and conspicuous); sculpture of gastral dorsum variable: 912
912a. Dorsum of basal gastral segment with longitudinal costulae only at base, otherwise smooth and shining; short, spatulate, reclinate ground hairs of gastral dorsum abundant and conspicuous: extirpa
912b. Dorsum of basal gastral segment longitudinally striolate for its full length; reclinate ground hairs of gastral dorsum obsolete or apparently so: fairchildi
938a. outer margins of mandibles relatively bowed; head length 0.75; mandibles relatively long (MI 67): lalassa
938b. Outer margins of mandibles relatively straight; head length < 0.60mm; mandibles relatively shorter (MI 60 or less): 943
943a. Mandibles short and thick (MI < 56); robust species, worker HL mostly > 0.48mm: 948
943b. Mandibles longer and slender (MI 56 or more); smaller species, worker HL mostly 0.48 or less: 969
948a. Mandible with exactly 3 small preapical teeth; ground pilosity of head nearly or quite obsolete: trieces
948b. Mandible with > 3 preapical teeth or denticles; ground pilosity abundant and conspicuous on head: subedentata
969a. Ventral spongiform appendages of postpetiole small but distinctly developed; gastral dorsum predominantly smooth and shining: gundlachi
969b. Ventral spongiform appendages of postpetiole absent; gastral dorsum with fine, mostly opaque reticulation: eggersi
Literature Cited
Brown, W. L., Jr. 1962. The Neotropical species of the ant genus Strumigenys Fr. Smith: Synopsis and keys to the species. Psyche 69:238-267.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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