Key to Royidris workers

This worker key is based on: Bolton, B. & Fisher, B.L. 2014. The Madagascan endemic myrmicine ants related to Eutetramorium (Hymenoptera: Formicidae): taxonomy of the genera Eutetramorium Emery, Malagidris nom. n., Myrmisaraka gen. n., Royidris gen. n., and Vitsika gen. n. Zootaxa 3791:1–99. doi:10.11646/zootaxa.3791.1.1

The genus Monomorium has recently been determined to have included Malagasy species that are now reorganized into the genera: Monomorium, Royidris, Syllophopsis and Trichomyrmex. Heterick (2006) revised the Monomorium before this taxonomic reorganization and prior to the description of new Royidris species that form part of the publication that includes the key given below. Heterick also included a key to the known Malagasy Monomorium (found here: Key to Malagasy Monomorium, Syllophopsis and Trichomyrmex species). If the key here is not resolving specimens adequately you may want to try this other key to see if you have a species that is close to but not Royidris.

Royidris shuckardi is not included in this key as it is only known from the queen caste.

You may also be interested in
 * Royidris
 * Royidris species groups
 * Key to Eutetramorium group genera
 * Monomorium
 * Syllophopsis
 * Trichomyrmex

1

 * Antennal club of 4 segments: in general, funiculus segments 8 and 9 appear very similar in length and volume. Funiculus segment 8 appears distinctly larger and more voluminous than segment 7. Segment 8 is disproportionately enlarged, out of proportion with the gradual increase in size of funiculus segments 4–7 . . . . . 2


 * Antennal club of 3 segments: in general, funiculus segment 8 appears distinctly smaller and less voluminous than segment 9. Funiculus segment 8 is only slightly larger than segment 7. Size of segment 8 is in proportion with the gradual increase in size of funiculus segments 4–7 . . . . . 8

2
return to couplet #1
 * With head in full-face view the dorsum between and behind the eyes with conspicuous sculpture present. Mid-dorsal strip of head, behind the frontal carinae, distinctly more strongly sculptured than the clypeus. Scape averaging shorter, SI 95–117 . . . . . 3


 * With head in full-face view the dorsum between and behind the eyes smooth or very nearly so, at most the surface with vestigial punctulate sculpture or superficial microreticulate patterning. Mid-dorsal strip of head, behind the frontal carinae, as smooth as, or only fractionally more sculptured than, the clypeus. Scape averaging longer, SI 115–158 . . . . . 5

3
return to couplet #2
 * With mesosoma in profile, the longest setae on the promesonotal dorsum are distinctly longer than the maximum vertical diameter of the eye at its midlength. Propodeal dorsum with 2 or more pairs of short, standing setae . . . . . Royidris longiseta


 * With mesosoma in profile, the longest setae on the promesonotal dorsum are distinctly shorter than the maximum vertical diameter of the eye at its midlength. Propodeal dorsum without standing setae, at most a few minute, decumbent pubescence hairs present . . . . . 4

4
return to couplet #3
 * Reticulate-punctate sculpture of cephalic dorsum strong and usually of uniform density everywhere. Pronotal dorsum densely reticulate-punctate, often also with weak transverse striolae; pronotal dorsum usually as strongly and densely sculptured as the propodeal dorsum. First gastral tergite superficially microreticulate. Scape and metatibia relatively shorter, SI 95–107 (mean SI 101), MfL/HW 0.95–1.06 . . . . . Royidris gravipuncta


 * Reticulate-punctate sculpture of cephalic dorsum fine and more diffuse, the sculpture may be partially or mostly effaced. Pronotal dorsum with reticulate-punctate sculpture very weak to effaced, never with transverse striolae; pronotal dorsum not as strongly or densely sculptured as the propodeal dorsum. First gastral tergite glassy smooth. Scape and metatibia relatively longer, SI 108–118 (mean SI 113), MfL/HW 1.08–1.13 . . . . . Royidris peregrina

5
return to couplet #2
 * Brown species with black gaster. Dorsum of head glassy smooth, with widely scattered minute punctures. Pronotal dorsum glassy smooth, without punctulate or microreticulate sculpture. Eyes smaller, EL/HW 0.28. Metafemur relatively shorter, MfL/HW 1.13 . . . . . Royidris singularis

Uniformly yellow species. Dorsum of head with superficial microreticulate or reticulate-punctulate sculpture, at least in part. Dorsum of pronotum partially to mostly microreticulate to punctulate. Eyes larger, EL/HW 0.29–0.32. Metafemur relatively longer, MfL/HW 1.25–1.50 . . . . . 6

6
return to couplet #5
 * Scape relatively very long, SI 148–158. Metafemur longer and somewhat less strongly incrassate, MfL/HW 1.46–1.50, MfL/MfH 4.00–4.38 . . . . . Royidris etiolata


 * Scape relatively shorter, SI 115–132. Metafemur shorter and somewhat more strongly incrassate, MfL/HW 1.25–1.39, MfL/MfH 3.36–4.15 . . . . . 7

7
return to couplet #6
 * Larger species, HL 0.80–0.98, HW 0.65–0.81, SL 0.86–1.00, EL 0.20–0.24 . . . . . Royidris notorthotenes


 * Smaller species, HL 0.66–0.73, HW 0.50–0.58, SL 0.66–0.73, EL 0.16–0.18 . . . . . Royidris diminuta

8
return to couplet #1
 * Promesonotum in profile slopes gradually and shallowly posteriorly to the metanotal groove; propodeal dorsum behind the metanotal groove approximately continues the line of the promesonotum and is not strongly depressed below the level of the promesonotal dorsum. Postpetiole relatively broad, its maximum width in dorsal view 0.42–0.48 × HW . . . . . 9


 * Promesonotum in profile convex, swollen or dome-like, descending steeply posteriorly to the metanotal groove (or the junction of mesonotum and propodeum in species where the metanotal groove is suppressed); propodeal dorsum is strongly depressed below the level of the promesonotal dorsum and does not continue its line. Postpetiole relatively narrow, its maximum width in dorsal view 0.33–0.38 × HW . . . . . 10

9
return to couplet #8
 * Dorsum of pronotum without a seta at the humeral angle. Posterior face of petiole node without setae. First gastral tergite without setae except for a few at the extreme apical margin. With head in full-face view the dorsum smooth and polished, with scattered minute punctulae on a glossy surface . . . . . Royidris depilosa


 * Dorsum of pronotum with a standing seta at the humeral angle. Posterior face of petiole node with a pair of setae. First gastral tergite with scattered setae, located anterior to those at the extreme apical margin. With head in full-face view the dorsum densely microreticulate to reticulate-punctulate everywhere . . . . . Royidris admixta

10
return to couplet #8
 * Dorsum of head between and behind the eyes sculptured, the surface either finely reticulate-punctate or densely shagreenate-striolate . . . . . 11


 * Dorsum of head between and behind the eyes unsculptured, the surface smooth except for minute and widely scattered pits . . . . . 12

11
return to couplet #10
 * In profile the propodeal dorsum slopes downward posteriorly and is confluent with the declivity through a broad, shallow curve; without a pair of short, erect setae on the curve. Dorsum of head to the level of the posterior margins of the eyes finely, densely shagreenate and with weak, superficial striolae, the whole surface with a silky appearance. Posterior to the level of the eyes the shagreenate component weaker and the striolae tend to be transverse. Pronotal dorsum shagreenate-striolate. Full adult colour of head and mesosoma yellow. Metafemur shorter and more strongly incrassate, MfL/HW 1.07–1.09, MfL/MfH 3.86–4.50 . . . . . Royidris robertsoni


 * In profile the propodeal dorsum horizontal, not sloped downward posteriorly; dorsum meets the declivity through a blunt right-angle; with a pair of short, erect setae on the dorsum just before the angle. Dorsum of head everywhere superficially punctulate to reticulate-punctulate, without a silky appearance. Pronotal dorsum mostly smooth, with only feeble superficial punctulae present. Full adult colour of head and mesosoma brown to dark brown. Metafemur longer and less strongly incrassate, MfL/HW 1.17–1.22, MfL/MfH 5.50–5.64 . . . . . Royidris anxietas

12
return to couplet #12
 * With mesosoma in profile the metanotal groove distinctly impressed; a V-shaped or narrowly U-shaped conspicuous impression present between base of mesonotum and propodeum. Mandible smooth, with scattered small pits. With head in full-face view the eyes distinctly in front of the midlength of the side of the head capsule. Eye smaller, EL/HW 0.22–0.26. Metafemur shorter and more incrassate, MfL/HW 0.93–1.04, MfL/MfH 3.67–4.00 . . . . . Royidris clarinodis


 * With mesosoma in profile the metanotal groove not impressed; without a V-shaped or narrowly U-shaped impression between base of mesonotum and propodeum. Mandible with fine longitudinal costulae. With head in full-face view the eyes very close to the midlength of the side of the head capsule. Eye larger, EL/HW 0.28–0.32. Metafemur longer and less incrassate, MfL/HW 1.12–1.32, MfL/MfH 5.60–6.00 . . . . . 13

13
return to couplet #12
 * Head and mesosoma uniformly yellow, gaster paler, very pale yellow. Lower half of side of pronotum without punctate sculpture such as occurs on the mesopleuron. Smaller species with relatively shorter scape, smaller eye, and shorter metafemur, HW 0.50, SL 0.50, SI 100, EL/HW 0.28, MfL/HW 1.12 . . . . . Royidris pallida


 * Head and mesosoma brown, gaster darker, black. Lower half of side of pronotum with punctate sculpture similar to that present on mesopleuron. Larger species with relatively longer scape, larger eye, and longer metafemur, HW 0.59, SL 0.66, SI 112, EL/HW 0.32, MfL/HW 1.32 . . . . . Royidris pulchra