Nylanderia mosaica Williams, Williams, Lapolla & Lucky, 2025, sp. nov.

Nylanderia mosaica, sp. nov. Figs. 52–54 (worker); Figs. 55–56 (queen) Holotype worker, COSTA RICA: Alajuela, 10km E of Monteverde, 10.30971 -84.72004, ±50m, elev. 890m, wet forest, sifted litter, 18.v.2014, J.T. Longino #JTL8692-s (USNM: USNMENT01131335). 1 paratype worker and 1 paratype queen with same locality data as holotype (USNM: USNMENT01130940, USNMENT01131335). 3 paratype workers, COSTA RICA: San José, Cerro Plano, 9.48264 -83.96259 ±10m, elev. 1070m, 4.vii.2015, ridgetop cloud forest, isolated peak with oak trees, leaf litter, ADMAC#Wa-E-06-2-25 (MNCR: USNMENT01131333, USNMENT01131334, USNMENT01131848). Worker diagnosis: Antennae relatively short, with scapes surpassing posterior margin by about a quarter of their length; bicolored, with yellow to yellow-brown head and mesosoma and medium to dark brown gaster; meso- and metacoxae yellow and at most somewhat lighter than mesosoma; light cuticular microsculpture resulting in subtle blue iridescence on head, mesosoma, and gaster; moderate cephalic pubescence. Compare with: N. mendax, N. usul WORKER. Measurements (n=9): TL: 1.70–2.01; EL: 0.09–0.12; EW: 0.07–0.10; IOD: 0.30–0.34; HE: 0.00– 0.01; HL: 0.52–0.57; HW: 0.42–0.49; HLA: 0.18–0.20; HLP: 0.23–0.27; SL: 0.59–0.65; PW: 0.32–0.36; MW: 0.17–0.19; PrW: 0.24–0.28; PDH: 0.17–0.30; PTW: 0.10–0.14; LHT: 0.50–0.56; WL: 0.60–0.70; GL: 0.58–0.76; SMC: 9–12; PMC: 2–3; MMC: 2–3. Indices: BLI: 139–148; CI: 82–88; EPI: 72–81; HTI: 112–119; REL: 17–21; SI: 127–139. Color: bicolored, with yellow to yellow-brown head and mesosoma and medium to dark brown gaster; black macrosetae strongly contrasting with overall color; meso- and metacoxae yellow and at most somewhat lighter than mesosoma; overall cuticle lightly microsculptured, resulting in subtle blue iridescence on head, mesosoma, and gaster. Pilosity: erect macrosetae on scapes abundant, long, and dark, strongly contrasting with fine, appressed pubescence; moderate cephalic pubescence, found laterally and concentrated around compound eyes; pubescence sparse to absent between compound eyes; mesosoma pubescence sparse to absent, limited at most to scattered hairs on pronotum and propodeum, and a fringe of hairs concentrated just posterior to the metanotal groove; gaster pubescence sparse to absent; pair of small, erect setae on apex of petiole. Head: longer than broad and quadrate with distinct posterolateral corners and flattened posterior margin, with little to no medial emargination; scapes surpass posterior margin of head by about a quarter of their length; all three ocelli absent or not apparent. Mesosoma: posterior margin of pronotum forming obtuse angle with anterior margin of mesonotum in profile view; propodeum low and evenly rounded, with posterior face about same length as dorsal face. QUEEN. Measurements (n=1): TL: 3.51; EL: 0.21; HL: 0.68; HW: 0.68; SL: 0.80; WL: 1.29; GL: 1.54. Indices: BLI: 190; CI: 99; REL: 30; SI: 119. Moderately sized. Color: bicolored, with light yellow-brown mesosoma and medium to dark yellow-brown head and gaster; meso- and metacoxae concolorous with mesosoma. Pilosity: most of body covered in moderate to dense pubescence; lacking pubescence laterally on pronotum, on most of anepisternum except for dorsal edge, and posterior face of propodeum; 8-10 small, erect setae on anepisternum. Other material examined: COSTA RICA: San José, Cerro Plano, 9.48264 -83.96259 ± 10m, elev. 1070m, 4.vii.2015, ridgetop cloud forest, isolated peak with oak trees, leaf litter, ADMAC#Wa-E-06-2-25; Cartago, PN Tapantí, 9.73699 -83.78176 ± 20m, elev. 1330m, 6.vi.2015, cloud forest, old 2nd growth, riparian, leaf litter, ADMAC#Wm-E-01-1-02. Etymology: The species epithet is derived from ‘ musaicum ’ (L. = mosaic), referring to this species’ bicolored appearance. Notes: Nylanderia mosaica workers most strongly resemble those of N. mendax and N. usul in appearance, though N. mosaica workers are easily separable based on their relatively small body size and bicolored appearance, with a yellow to yellow-brown head and mesosoma and medium to dark brown gaster. This species is only known to moderate to high elevation forests in Costa Rica (Fig. 2B), where it is sympatric with only N. usul and no other species in American Clade I.