The preimaginal stages of the following species were studied for the first time (the origin of specimens used for rearing is indicated). They were obtained in laboratory by rearing adults collected from field, except for Platydracus p. pseudopatricius, in which the larvae were collected in the field and reared to adults.

Algon sphaericollis Schillhammer, 2006: collected from November 2021 to October 2022 by sifting the forest leaf litter in Minhang, Shanghai, China (31°1′11″N 121°28′1″E).

Philonthus spinipes Sharp, 1874: collected from November 2021 to October 2022 by sifting the forest leaf litter in Minhang, Shanghai, China (31°1′11″N 121°28′1″E).

Platydracus pseudopaganus pseudopatricius (Müller, 1926): collected on June 3, 2021 by sifting in the bamboo forest of Sheshan Mountain, Shanghai, China (31°6′12″N 121°12′3″E).

Platydracus marmorellus (Fauvel, 1895): collected on August 10, 2021 from Qingchengshan Mt., Sichuan, China (30°54′38″N 103°34′26″E).

Saniderus cooteri Rougemont, 2015: collected on May 1, 2021 in Ruyuan, Shaoguan County, Guangdong, China (24°55′56″N 113°1′41″E).

Eucibdelus sp.: collected on May 1, 2021 in Ruyuan, Shaoguan County, Guangdong, China (24°55′56″N 113°1′41″E).

Saniderus sp.: collected on August 3, 2021 by sifting in the bamboo forest near the expressway of Xiling snow mountain of Sichuan, China (30°37′39″N 103°23′8″E).

Field collected adults or larvae of each species were placed in a plastic container filled with humid soil and covered with moist tissue. When the daily temperature reached 20°C, females and males were paired in boxes for mating. After oviposition, the eggs were placed separately in plastic boxes filled with moist tissue (laboratory temperature 22 ± 2°C) for daily observation. Hatched larvae were kept in a plastic box covered with moist tissue. Blatta lateralis (Walker, 1868) were supplied as food for both adults and larvae. Development time at each stage was recorded. When larvae of successive instars and prepupae were obtained, several individuals that reached those stages were killed and preserved.

For morphological descriptions, a few larvae of each instar were killed with boiling water and immediately after killing placed in a groove of an acrylic plate filled with 75% ethanol and covered with a cover glass. After removing air bubbles, they were photographed using Canon macro photo lens MP-E 65 mm attached to a Canon EOS7D camera; photographs were stacked with Zerene Stacker.

For detailed morphological studies, several larvae of each instar were decapitated, macerated in boiling 10% KOH, rinsed in distilled water, dried by ethanol gradient dehydration, and mounted in Euparal (Chroma Gesellschaft Schmidt, Koengen, Germany) on plastic slides. Photos of taxonomic characters were taken with a Canon G9 camera attached to an Olympus SZX 16 stereoscope. Some of the features used for morphological research were drawn for clearer outlines. To obtain the microscopic structure of eggs and larva, samples were dried by ethanol gradient dehydration, and scanned by HITACHI UHR FE-SEM SU 8000 scanning electron microscope. The material used for each species is listed in Table 1. Voucher specimens are deposited in the Department of Biology, Shanghai Normal University, P. R. China (SHNU).

The life cycle of Algon sphaericollis in Shanghai was studied from November 2020 to October 2022 by rearing in the laboratory with simultaneous observation in the field. Adults were searched every ten days in the field by turning over rocks and sifting leaves. Habitat preferences were investigated in the field.

Compared with adults, the morphological terminology of immature stages of Staphylinidae is still not unified. We follow Schmidt (1996) and Staniec et al. (2009) for the terminology of the structures of egg, larva and pupa, functional organs, sclerites and setae, and Solodovnikov and Newton (2005) for the terminology of the larval thorax. The terminology of chaetotaxy follows Ashe and Watrous (1984), Solodovnikov and Newton (2005) and Pietrykowska-Tudruj et al. (2014). Only the detailed morphological study of A. sphaericollis is presented in this paper. The second instar larvae (L₂) of A. sphaericollis are very similar to the L₃ larvae and are hence not described.

For the phylogenetic analysis, we combined the species we reared by ourselves, and those described in the literature. Considering that the larval studies of Ontholestes murinus by Paulian (1941) and Potoskaya (1967) lack a lot of important morphological data, the morphology of this species was coded based on the examination of the third instar larvae deposited in the Zoological Museum of the University of Copenhagen, Denmark by Qing-Hao Zhao. The microstructure of the egg of Philonthus spinipes was examined with the help of Mateusz Sapieja (Museum of Natural History, University of Wroctaw, Poland). The following 71 characters were coded for 40 terminal taxa:

1. Egg, shape: (0) Broadly oval, surface without any distinct structures; (1) with longitudinal ridges; (2) with crescent-shaped contact disc anteriorly; (3) with transverse ridge; (4) with numerous pointed projections.

2. Egg, aeropyles: (0) distinct; (1) absent or invisable.

3. Egg, aeropyles, arrangment: (0) uniformly scattered; (1) longitudinally ​arranged in several rows; (2) irregularly scattered (3) densely formed band.

4. Egg, aeropyle band, shape: (0) equatorial band; (1) wave-like band.

5. Egg, wave-like aeropyle band: (0) divided; (1) undivided.

6. Egg, transverse ridge: (0) extending over the whole length of equator, forming a closed ring; (1) extending about one third length of equator.

7. Head capsule, length/wide (without neck): (0) distinctly longer than wide; (1) almost as long as wide.

8. Head capsule, ventral ecdysial line: (0) Y-shaped; (1) anterior arms atrophied.

9. Head capsule, apotome: (0) with stalk; (1) without stalk.

10. Head capsule, tentorial pits: (0) placed anteriorly; (1) placed centrally; (2) placed posteriorly.

11. Head capsule, frayed or club-shaped setae: (0) abscent; (1) present.

12. Head, epicranial gland; (0) present; (1) absent.

13. Head, position of macro epicranial dorsal setae: (0) the connection between the two setae divides the medial ecdysial line (without neck) into a shorter front half and a longer back half, with a ratio of the two less than 0.5 (Fig. 15M); (1) the connection between two setae divides the ecdysial line into two segments of almost equal length, with the ratio of the front half to the back half between 0.5 and 1 (Fig. 15L). (2) the connection between two setae almost reach to the bottom of nasale.

14. Nasale, number of teeth: (0) 9; (1) 7; (2) 11

15. Nasale, median tooth: (0) distinct; (1) barely visible.

16. Antennae, segment IV: (0) longer than sensory appenda ge; (1) shorter than sensory appendage.

17. Antennae, sensory appendage located: (0) inner laterally; (1) ventrally; (2) outter laterally.

18. Antenna, sclerotized band of main sensory appendage: (0) present; (1) absent.

19. Ligula: (0) sclerotised; (1) unsclerotised.

20. Maxillae, setae on inner margin of segment II of maxillary palp, position: (0) apical, within top 1/3; (1) middle; (2) lower middle, about 1/3 of the base; (3) lower, less than 1/4 of the base.

21. Maxillae, digitiform sensory appendage location: (0) at base of segment III; (1) anteriorly, closer to apex.

22. Maxillae, mala: (0) as long as or longer than segment I of maxillary palp; (1) shorter than segment I of maxillary palp but longer than 1/3 the maxillary palp segment I; (2) shorter than 1/3 the maxillary palp segment I.

23. Maxillae, mala, apical setae: (0) present; (1) absent.

24. Maxillae, mala, number of apical setae: (0) 1; (1) 2; (2) 3.

25. Maxillae, mala, setae on inner magin: (0) present; (1) absent.

26. Maxillae, mala, setae on outer magin: (0) present; (1) absent.

27. Maxillae, mala, setae near base: (0) present; (1) absent.

28. Maxillary palp and labial palp, last segment: (0) with notch of thinner sclerotization, (1) without notch of thinner sclerotization.

29. Maxillary palp and labial palp: (0) four and three segments, respectively; (1) three and two segments, respectively; (2) three and three segments, respectively.

30. Labial palp, segment I: (0) with pore, (1) without pore.

31. Stemmata (if not atrophied): (0) four pairs; (1) six pairs; (2) one pair; (3) three pairs.

32. Prothorax, spiracal appendage: (0) absent; (1) present.

33. Prothorax, frayed or club-shaped setae: (0) absent; (1) present.

34. Meso- and metathorax, frayed or club-shaped setae: (0) absent; (1) present.

35. Protibia: (0) length/width between 4 and 6, parallel-sided at two thirds of base or slightly dilate at middle; (1) tubby, length/width < 4, dilated anteriorly; (2) very slender, almost as long as femur, length/width > 6, widest near base, gradually tapering toward front; (3) very slender, almost as long as femur, length/width > 6, widest at 1/3 base, then suddenly taper toward front.

36. Protibia, type of setae: (0) scattered big spines, rarely with smaller spines; (1) numerous short setae; (2) densely distributed large spines, with smaller spines scattered among them.

37. Bifurcate setae on protibia: (0) present; (1) absent.

38. Protibia, comb: (0) present; (1) absent.

39. Protibia, rows of comb: (0) single; (1) multipal.

40. Protibia, comb, type of setae: (0) bifurcate; (1) simple.

41. Foreleg, tarsungulus: (0) fused with tibia; (1) not fused with tibia.

42. Foreleg, tarsungulus, number of spine-like setae: (0) 2; (1) 3; (2) 4; (3) 8.

43. Foreleg, tarsungulus, bifurcate setae: (0) present; (1) absent.

44. Foreleg, tarsungulus, spine-like setae on dorsal side: (0) absent; (1) present.

45. Foreleg, tarsungulus, spine-like setae on dorsal side: (0) as long as ventral setae; (1) longer than ventral setae.

46. Foreleg, trochanter, length of spine-like setae on ventral front: (0) at least twice the thickness of trochanter; (1) less than twice the thickness of trochanter.

47. Abdominal paratergites of segment II–VIII: (0) fused as a whole; (1) divided into two parts.

48. Abdominal, paratergites and parasternites of segment I: (0) present; (1) absent.

49. Abdominal, paratergites and parasternites of segment I, shape: (0) similar with segment II-VIII; (1) differed from segment II-VIII.

50. Abdominal, paratergites and parasternites of segment I: (0) paratergites bend toward the parasternites; (1) paratergites in their usual form, parasternites reduced into tiny fragments, with an additional posterior sclerite emerging between them (Fig. 16K); (2) paratergites and parasternites seamlessly merge forming U-shaped lateral sclerites; (3) paratergites and parasternites fused with more distinct boundaries at the smaller parasternites.

51. Abdominal, posterior carina of tergite I: (0) absent; (1) present.

52. Abdominal, tergites, setae on segment II–VIII, (0) only frayed or club-shaped; (1) frayed or club-shaped and simple; (2) only simple.

53. Abdominal, sternites, setae on segment II–VIII, (0) only frayed or club-shaped; (1) frayed or club-shaped and simple; (2) only simple.

54. Urogomphi: (0) longer than pygopod; (1) 0.3–0.8 × as long as pygopod; (2) 0.9–1.1 × as long as pygopod.

55. Urogomphi: (0) 2 segments; (1) not segmented, fusiform; (2) not segmented, whip-like.

56. Urogomphi, segment I, frayed or club-shaped setae: (0) present; (1) absent.

57. Urogomphi, segment I, simple macro setae: (0) present; (1) absent.

58. Urogomphi, segment II, frayed or club-shaped setae: (0) present; (1) absent.

59. Pygopod, shape: (0) short, 1.1–1.8 as long as wide; (1) moderately elongate, 2.1–3.1 as long as wide.

60. Pupae, Setiform projections or spines on body (excluding segment IX): (0) present; (1) absent.

61. Pupae, protuberances on pronotum: (0) present; (1) absent.

62. Pupae, setiform projections on pronotum: (0) present; (1) absent.

63. Pupae, protuberances on mesonotum: (0) present; (1) absent.

64. Pupae, cuticular processes on sides of abdominal segment VII: (0) present; (1) absent.

65. Pupae, cuticular processes on sides of abdominal segment VIII: (0) present; (1) absent.

66. Pupae, type of cuticular processes on sides of abdominal: (0) setiform projections; (1) spines.

67. Pupae, terminal prolongations of segment IX: (0) present; (1) absent.

68. Pupae, apical accessories of terminal prolongations: (0) present; (1) absent.

69. Pupae, shape of apical accessories: (0) straight; (1) curved.

70. Pupae, apex of apical accessories: (0) pointed; (1) rounded.

71. Pupae, first pairs of functional spiracles: (0) in the same longitudinal line as others; (1) protruding laterally much more than others.

Information about the morphology of immature stages of other species used in the analysis (26 genera of Staphylininae representing 7 tribes sensu Żyła and Solodovnikov 2020) is extracted from the literature; members of Platyprosopinae and Xantholininae are added as outgroups (Table 2). A data matrix of 71 morphological characters including eggs, mature larvae (or L₂ when mature larvae were unavailable) and pupae is coded for 40 terminal taxa (File S1). Inapplicable characters are marked by ‘–’ and treated equivalent to missing data (?). The majority of terminal taxa are comprised of a single species, with exceptions of genera which species share the same morpohlogy (e.g., Saniderus, Arrowinus, and Erichsonius) or when morphology data of a species with incomplete information can be completed by the data of other species of the same genus (e.g., the data of Xanthopygus were extracted from the data matrix of Solodovnikov (2005) and complemented data provided for X. cognatus by Quezada et al. 1969). The data matrix was imported into TNT 1.1. (Goloboff et al. 2008) and analyzed with equally weighted parsimony and traditional search: the memory was set to hold 10000 trees, 1000 replicates with tree bisection-reconnection (TBR) swapping and holding 10 trees per replicate. The results were visualized in WinClada v. 1.00.08.

Egg (Fig. 2A, B). Early stage: Length: 1.83–2.00 mm (mean 1.92 mm); width: 1.42–1.48 mm (mean 1.45 mm). Late stage: Length: 1.90–2.25 mm (mean 2.08 mm); width: 1.68–1.88 mm (mean 1.78 mm). Colour white, becoming gray and speckled as it develops. shape oval, expanding laterally along its development; half of its length with narrow transverse ridge forming a closed ring; surface rough, aeropyles invisible, with irregular granular protuberance (Fig. 2B).

Mature larva (L₃) (Fig. 2D–F). Body length (from anterior margin of nasale to end of pygopod): 15.96–17.70 mm (mean 16.70 mm); head width: 2.35–2.55 mm (mean 2.45 mm); head length (with posterior region): 2.96–3.18 mm (mean 3.10 mm). Head, tergites and ventral sclerotized plates of thorax, and abdominal tergites I-VIII dark brown; antennae, maxillae, labium, part of leg above trochanter yellowish brown; thoracic membrane white; coxae, trochanter, and abdominal membrane pale brown, abdominal pleurites and sternites slightly darker than membrane. Head wider than thorax, legs slender, abdominal segment I narrower than segment II, widest at segment III, urogomphi segment I as long as pygopod. — Head (Fig. 3A–H): Subparallel-sided, about as wide as long, widest at level of stemmata, prognathous with distinct neck; dorsal ecdysial line bifurcate in front 1/3 of head; each side of head with 4 stemmata in a cluster of equal size. Microsculpture on head with front part sparsely furrowed, gradually transitioning backward to scale-like (Fig. 2D, F). Epicranial part (Ep) with 16 pairs of setae, 1 pair of gland (Gl) (Fig. 3C) and 1 pair of pores; posterior area (Pa) with 3 pairs of micro setae (P1–3) and a pair of pores. Ventral side of head with 9 pairs of setae, 1 pair of pores (Fig. 3A), Nasale (Na) (Fig. 4A–C) with 10 pairs of setae, a pair of pores medially, a pair of lateral sensilla (Sm) laterally and a pair of glandular pits posterio-laterally; anterior margin with 9 rounded teeth, paramedian teeth (Pmt) largest, converging toward barely visible median tooth (Mt). Apotome (Ap) triangular, with stalk distinctly extending beyond linear tentorial pits (Tp) (Fig. 3B, E), with 3 pairs of setae, 2 pairs of pores. Epipharynx (Fig. 4D, E) with 3 pairs of olfactory organs each located at ventral side of paramedian teeth and first 2 lateral teeth, 2 bunches of cuticular processes (Cp) separated slightly from each other anteriorly, 1 row of cuticular processes posteriorly. Mandibles slender, with 2 setae at the outer margin and 2 sensillae (1 frontal, 1 lateral). Hypopharynx (Fig. 4D–M) with broad membranous dorsal side covered with long pubescence (Fig. 4H). Ligula (Fig. 4I, K) conical, distinctly wider at base than segment I of labial palp, margins with a pair of micro setae; sclerotized part of prementum (Pmnt) with 2 pairs of setae (Fig. 4M). Labial palpi (Lp) 3-segmented, length ratio of segments I, II, III = 3.6:3.4:1, respectively; segment I 4.2 times as long as wide, with 1 pore laterally (Fig. 4L); segment II 5.1 times as long as wide, segment III cone-shaped, 3 times as long as wide, tapered subapically, with a few micro sensory appendages apically (Fig. 4G). Antennae (Fig. 5G) 4-segmented, length ratio of segments I-IV = 1:3.6:2.4:1.3, respectively, segment I as wide as long; segment II 6 times as long as wide, with 1 pore ventrally; segment III 6.3 times as long as wide, with 3 macro setae, 2 sensory appendages (Sa) (one conical and the other tiny), 2 solenidia (So) and one pore; segment IV about 4.5 times as long as wide and 3.8 times as long as cone-shaped sensory appendage of segment III, with 3 setae and 4 solenidia (So) apically. Maxillae (Fig. 5A–E): length ratio of cardo (Cd): stipes (Stp) = 1:2; cardo 1.5 times as long as wide, bearing 1 seta ventro-laterally; stipes rectangular, 4.2 times as long as wide with 10 setae and 2 pores. Mala (Ma) (Fig. 5C) long, finger-shaped, with 2 setae (1 inner margin and 1 outter margin) and 1 pore, 4 sensory appendages (Fig. 5E) apically; length ratio of mala and segment I of maxillary palpi = 1.15:1. Palpifer with 1 pore and 1 seta ventrally. Maxillary palpi (Pm) 4-segmented; length ratio of segments I–IV = 2.2:2.9:2.8:1, respectively; segments I, II, III, IV 4, 4.8, 7.2, 4.2 times as long as wide, respectively, segment II with 2 setae laterally, segment III with 1 digitiform sensory appendage basally on outer margin, segment IV with a few micro sensory appendages on apex (Fig. 5D). — Thorax (Figs 6A–J, 7D–I): thoracic chaetotaxy of each instar is identical, thus only the setae of first instar larva (L₁) are coded): Pro-, meso- and metanotum (Fig. 6A, B) with mid-longitudinal ecdysial line; pronotum with posterior carina (Pc), meso- and metanotum with anterior carina (Ac) and Pc; microstructure of carina as in Fig. 6E. Pronotum (Fig. 6C) slightly wider than long, with 19 pairs of setae (8 macro simple, 1 frayed, 10 micro) and 10 pores and a pair of probably coeloconic sensillum (Cs) (Fig. 6D–G); mesonotum (Fig. 6C) wider than long, chaetotaxy composed of 7 macro simple setae, 2 frayed setae (13, 18), 14 micro setae (1, 2, 3, 4, 12 situated on cuticle along anterior and lateral margin of tergite), 4 pores and 1 pair of pretergal glands (Ptg). Metanotum similar to mesonotum in chaetotaxy but missing 1 microseta anteriorly. Prothorax ventrally with large triangular cervicosternum (Sc), a pair of episterna (Eps) postero-lateral to cervicosternum, a pair of cuniform lateral sclerites (Ls) between cervicosternum and episterna, and two pairs of small postcoxal sclerites (Pcs) (1 close to the spiracle, the other medially). Cervicosternum with 5 pairs of setae. Episternum, lateral sclerite and postcoxal sclerite each with 1 seta. Ventral side of meso- and metathorax each with a pair of episterna (Eps) and a pair of epimeron (Em) connected by pleural apophysis (Pa). Mesothorax with a pair of small round additional ventral sclerites (Avs) anteriorly, next to episterna, and an islands of small Avs posteriorly each with one micro-seta, next to Pcs, while metathorax without anterior Avs and Pcs, posterior Avs merge into two pieces. Ventral membranous surface of each thoracic segment with a pair of setae (1 medially, the other close to coxa) and a pair of sternal apophyseal pits (Sap). Leg 5-segmented. Fore leg (Fig. 7D–G): length ratio of coxa : trochanter : femur : tibia : tarsungulus = 3.6:1.2:3.5:2.9:1, respectively. Coxa strong, with about 20 setae (6 large) and 2 pores; trochanters (Tr) with several pores and 9 setae, the apical one the largest. Femur (Fe) with about 26 setae; large spine-shaped setae arranged in 2 rows ventrally. Tibia (Tb) slender, with 28 setae, large spine-shaped setae mainly arranged in dorsal and ventral rows, and a comb of bifurcate setae arranged diagonally near apex of anterior aspect (Fig. 7F, G). Tarsungulus (Tu) with 3 spine shaped setae. Mid and hind legs longer than fore leg, with chaetotaxy similar to that of fore leg but without bifurcate setae (Fig. 7H, I). — Abdomen (Figs 8A–C, 9): segments I–VIII each with divided tergite (Te) and sternite (St), a pair of spiracle (Sp), a pair of paratergites (Pt) and parasternites (Ps) laterally; segment I with transverse carina anteriorly and wide band of more weakly sclerotized cuticles posteriorly, and on segments II–VIII the cuticle bands gradually narrow and disappear. Spiracles of segment I larger than spiracles of segments II–VIII. On segment I paratergites and parasternites posteriorly fused to form U-shaped lateral sclerites (Fig. 8B), paratergites of segment II–VIII divided into a main part and an additional lateral sclerites. Segment I: tergite with 23 pairs of setae (10 macro club-shaped, 13 micro simple) and 6 pores; sternites with 14 pairs of setae (9 macro and club-shaped, 5 micro and simple) and one pore; paratertites and parasternites with 7 setae (3 macro and club-shaped); segments II–VIII: tergites with 23 pairs of setae (10 macro club-shaped, 7 medium sized club-shaped, 14 simple and micro); sternites with 16 pairs of setae (2 macro and simple, other frayed or club-shaped) and 5 pairs of pores; paratergites with 5 setae (3 club-shaped and 2 micro) on the big sclerite and 1 club shaped seta on the small one; parasternites with 7 setae (6 club-shaped and 1 micro). Type of setae on abdominal segments as on Fig. 8G–K. Abdominal segment IX with 10 pairs of setae (4 club-shaped and 6 micro) on tergite and 6 pairs of setae on sternite (1 club-shaped, other simple), with two long, articulated, 2-segmented urogomphi (Fig. 9). Segment I of urogomphi about twice as long as abdominal segment IX, with about 20 setae, 2 of them frayed (Fig. 9G), segment II slender, about half as long as segment I, with two simple setae, (one long, the other much shorter) at apex. Surface of urogomphi with numerous tiny stylus (Fig. 9C). Abdominal segment X (pygopod) about as long as segment I of urogomphi, with about 26 pairs of setae, many of which frayed (Fig. 9F). Surface of pygopod with numerous sharp cuticular protuberance (Fig. 9B).

First instar larva (L₁) (only characters listed that are different from those of mature larva). Body length: 9.1–12.0 mm (mean 10.3 mm); head width: 1.69–2.01 mm (mean 1.95 mm); head length: 1.79–2.18 mm (mean 2.15 mm). Head reddish brown, tergites and ventral sclerotized plates of thorax, and abdominal tergites I–VIII brown (Fig. 2C). — Head (Fig. 3I–K): inverted trapezoid, widest at level above stemmata then tapering towards neck, chaetotaxy as in Fig. 3I–K (same as in mature larva); microsculpture on head not as distinct as mature larva. Length ratio of antennomeres (Fig. 5H–J) I–IV = 1:3.4:2.7:1.2, segment IV about 3.2 times as long as wide and 2.2 times as long as cone-shaped sensory appendage of segment III, Maxillae (Fig. 5F): cardo 2 times as long as wide, stipes with 8 setae and 2 pores. Length ratio of mala and segment I of maxillary palpi = 1.3:1. length ratio of segments I–IV of maxillary palpi (Pm) = 1.7:2.8:2.3:1, respectively; segments I, II, III, IV 3.2, 4.2, 7.2, 4.2 times as long as wide. Mandible similar to that of mature larva (Fig. 5K–M). — Thorax (Fig. 6K, L): structure and chaetotaxy of thoracic segments similar to that of mature larva. Fore legs (Fig. 7A–C) slightly thicker than in mature larva, length ratio of procoxa : trochanter : femur : tibia : tarsungulus = 2.1:0.85:2.0:1.75:1, respectively. Setae of femur and tibia much less than in mature larva, fore tibia without bifurcate setae. — Abdomen (Fig. 8D–F): tergites I–VIII without weakly sclerotized cuticle band posteriorly present in L₃; number of macro club-shaped setae of tergite I same as in L₃ (4, 10, 11, 13, 18, 19, 20, 21, 22, 23), simple setae less than in L_3; macro club-shaped setae of tergite II–VIII identicle to L₃ (4, 9, 10, 12, 17, 18, 19, 20, 22, 23), other setae less than in L₃. Sternite I with same club-shaped setae as L₃, without micro setae; segment II lack of the central area setae (8, 9, 12, 13) present in L₃. Paratertites and parasternites (Fig. 8E) of segment I identical to L₃, segment II missing 1 and 2 setae on paratergites and parasternite, respectively. Segment IX and X similar to that of L₃.

Pupa (Fig. 10). Colour orange, cuticula well sclerotized. Body length (without terminal process): 8.86–10.21 mm (mean 9.90 mm); body width in the widest place (between hind knees): 4.2–4.5 mm (mean 4.35 mm); head width (between eyes): 2.2–2.7 mm (mean 2.56 mm); head length: 3.2–3.6 mm (mean 3.4 mm); pronotum width: 3.0–3.3 mm (mean 3.18 mm); pronotum length: 2.7–3.0 mm (mean 2.9 mm). Mandibles crossed at apices. Antennae curved, protruding slightly beyond half-length of elytra. Anterior margin of pronotum with 16 setiform projections, about half of pronotum length. Surface of pronotum uneven, with a pair of pores subantero-laterally (Fig. 10D). Wings reaching posterior margin of abdominal segment III. Meso- and metatibiae with about 16 and 6 protuberances, respectively. Protarsi reaching level of apices of maxillary palps, mesotarsi almost reaching level of apices of wings, metatarsi protruding slightly beyond anterior margin of abdominal segment VII. Abdomen moderately and gradually widening to segment IV and then tapering to terminal segment of the body. Abdominal tergite I twice as long as tergite II. Abdominal segments VII and VIII each bearing on sides a pair of long, curved, setiform projections, projections on segment VII longer than those on VIII. Terminal sternite with well-marked sexual dimorphism (Fig. 10E, F). Female pupa (Fig. 10F) with double gonotheca (Gt) and ventral prolongations (Vp); male pupa (Fig. 10E) with single gonotheca; terminal prolongation of both sexes with straight accessory (A) with apex rounded (Fig. 10E, F, apex of male broken off). Abdominal tergites I–IV with functional spiracles, tergites V–VIII with atrophied spiracles (Fig. 10B).

The morphology of six Staphylinini species was studied using the same methods as employed for Algon sphaericollis. Photographs of selected species, which were not described in detail but were solely utilized for phylogenetic analysis and morphological comparisons in this study, can be found in Figs 11 and 12.

The analysis, based on immature stages, which included characters of egg, larva, and pupa, yielded 841 most parsimonious trees with the length of 230 steps. The strict consensus tree (Fig. 13A) revealed monophyletic Tanygnathinini, Acylophorini and Staphylinini. The other tribes, such as Quediini represented by 4 species, and Amblyopinini represented by 3 species, were not retrieved. Natalignathus was strongly supported as the sister group of Tanygnathinini, which corresponds to its speculated position proposed by Shaw et al. (2020). The placement of Quedius antipodum within Amblyopinini was previously supported by adult characters and DNA (Shaw et al. 2020). However, the larval data do not support this conclusion, as was the case in the study by Pietrykowska et al. (2014), and strongly support the placement of Q. antipodum in Staphylinini. The relationships between tribes remained unresolved, but Acylophorini were supported as the sister group of Antimerus + Astrapaeus. Within the Staphylinini, the monophyly of Philonthina and Staphylinina was supported, but the internal topology within these subtribes remained unresolved. The 50% majority rules consensus tree corresponds well to the strict consensus tree based on DNA and adult morphology by Chani-Posse et al. 2018 (Fig. 14A, B) in the position of Tanygnathinini, Amblyopinini, and Erichsonini as the early-branching groups and a strong support for Staphylinini as the crown group.

The analysis, based solely on 53 larval characters, found 333 trees with the length of 190 steps (Fig. 13B). Only Tanygnathinini (including Natalignathus) and Acylophorini were resolved at the tribe level. Staphylinini, Philonthina, and Staphylinina were not resolved. Additionaly, a clade including Abemus, Emus, Ontholestes, Platydracus and Saniderus emerged. This is consistent with previous studies grouping these genera together as the Platydracus group based on adult characteristics (Chani-Posse et al. 2019) or the combination of morphology and DNA (Brunke and Smetana 2019). When characters are mapped on the 50% majority rule consensus tree, it becomes evident that early branching clades possess numerous larval synapomorphies, while crown group members predominantly exhibit synapomorphies in pupae or eggs (Fig. 15). Tanygnathinini are characterized by posteriorly placed tentorial pits on the larval head capsule (character 10-2, Fig. 15A), and the spiracle appendage on the prothorax (character 32-1). Acylophorini can be identified by an anteriorly placed digitiform sensory appendage on maxillae (character 21-1, Fig. 15J). Pupal characters that distinguish Staphylinini from other tribes encompass setiform projections on the pronotum (character 62-0, Fig. 15F) and the sides of abdominal segments (character 66-0, Fig. 15G). Additionally, the apex of apical accessories on the terminal prolongations of segment IX is not pointed (character 70-1) in most species. The presence of uniquely curved apical accessories on the terminal prolongations of segment IX is a distinctive feature found exclusively in pupae of Staphylinina (character 69-1, Fig. 15P). The absence of terminal prolongations appears to be a potential synapomorphy of pupae of the Platydracus group, although further investigation is needed. The clades with strong support of pupal characters revealed by us correspond to those revealed by Staniec and Pietrykowska-Tudruj (2019) solely on pupal data. Eggs with longitudinally arranged rows of aeropyles are exclusively found in the Philonthina (character 3-1, Fig. 15K) and densely distributed aeropyles forming a band are exclusive for the Staphylinina (character 3-3, Fig. 15O). Interestingly, this band appears as an equatorial feature in Creophilus, Ocypus and Eucibdelus but transforms into a wave-like pattern in Staphylinus (Hinton, 1981). In most members of the Platydracus group, it forms an unbroken wave-like band, with the density of the wave varying among species and genera.

These findings suggest that, with the exception of highly derived groups such as Tanygnathinini, Acylophorini, and the Platydracus group, similar larval characters evolved or were lost multiple times in parallel, which diminish their phylogenetic signal. We speculate that the absence of egg and pupal data led to the placement of Quedius antipodum within Staphylinini in our analyses. Previous studies have found numerous larval characters useful for subtribe-level or even species-level idetification of the Staphylininae species (Kasule 1970; Staniec 2005b; Pietrykowska-Tudruj et al. 2014). In this study, we tested the phylogenetic significance of these characters and found that most are non-homologous traits, significant only when combined with others.

We focus on novel characters of potential phylogenetic importance, which may offer new insights into evolutionary connections. The presence of spine-like setae on the dorsal side of the tarsungulus (character 44-1, Fig. 15C) represents a synapomorphy of Staphylininae, as previously documented by Solodovnikov and Newton (2005). Notably, this trait is absent in Staphylinus, Platydracus group (44-0, Fig. 15R) and the outgroups, suggesting a potential reversal to the ancestral condition. The epicranial dorsal macrosetae (Ed2) situated at the mesoanterior region of the head in most Staphylininae (character 13-0, Fig. 15M) have shifted to the mesoposterior part of the head in many members of Philonthina (character 13-1, Fig. 15L). The presence of microsetae on the inner and outer margins of the mala (character 25-0, Fig. 15D) is common in Staphylininae of the Northern hemisphere clades, with exceptions of Acylophorus and Astrapaeus. However, these microsetae are notably absent in Philonthina (character 25-1, Fig. 15N). The spine-like macroseta on the ventral front face of the foreleg trochanter is exceptionally elongated in the Platydracus group (character 46-0, Fig. 15S), this feature is also present in Hypnogyra, an outgroup of Staphylininae.

Our analyses indicate that larval morpohlogy of the Staphylininae is a mosaic combination of homologous and analogous characters. It can be illustrated by the setae and other structures on the protibia. Boháč (1982) defined two morpho-ecological types of protibia for Staphylinina, the running and burrowing type. We extend this concept here to the whole Staphylininae and propose three protibial types:

(1) The running type: Protibiae are moderately long and slender (length : width ratio is 4–6), with parallel sides c. in basal two-thirds or with a slight dilatation at mid-length (Fig. 16A). This type is prevalent in early-branching and crown groups, particularly in Quediini and the majority of Staphylinini.

(2) The elongate running type: Protibiae are nearly as long as femora (length : width ratio > 6), widest near the base and gradually tapering towards apex (Fig. 16C). This type is more common in early-branching groups like Acylophorini, Astrapaeus, and Tanygnathinini. The shape is a bit modified in Tanygnathini: the protibial is slightly dilatated in the basal third and tapers suddenly towards the apex.

(3) The burrowing type: Protibiae short and wide, of the tubular shape (length : width ratio < 4), with an apical dilatation and dense coverage with prominent spines (Fig. 16B). Boháč (1982) originally observed this type in Platydracus, Ontholestes and Abemus, here we found it present in all members of the Platydracus group. Interestingly, a similar morphological adaptation is present in Arrowinus of Platyprosopinae, possibly indicating a case of convergent evolution.

The presence of bifurcate setae on the anterior aspect of the protibia is considered a plesiomorphic trait within Staphylininae (Pietrykowska-Tudruj et al. 2014) and its nearest relative, Arrowinus. Another supposedly plesiomorphic trait observed in Staphylininae and the closely related Xantholininae, is the comb-like structure composed of tiny setae arranged in lines or clusters on the tibia (Fig. 16F; for other species in Xantholininae, see Kasule 1970). Interestingly, the tiny setae constituting the comb are frequently substituted by bifurcate setae (Fig. 16G). Notably, these traits are subject to collective or individual loss within different taxa over evolutionary time. Classification based on tibial shape, comb presence, bifurcate setae presence, and bifurcate setae within the comb yields nine observed combinations (Fig. 16A–C). Of the taxa with the elongate running protibiae, Tanygnathinini lose both the comb and bifurcate setae. Astrapaeus features numerous bifurcate setae that do not form a comb structure (Fig. 16I). Acylophorini displays a protibial comb formed by bifurcate setae. Of the taxa with the running protibiae, Erichsonini, Quediini, Quedius antipodum, Algon, Xanthopygus, and Staphylinus all exhibit the protibial comb with bifurcate setae. In Ocypus, the character varies, with some species exhibiting bifurcate setae forming combs while others not (Kasule 1970; Boháč 1982). Eucibdelus lacks the comb but features small spines scattered on the anterior aspect of the protibia (Fig. 16D). Bifurcate setae are absent in all Philonthina, but in some larger species, combs composed of simple setae are present on the protibia, as observed in P. spinipes (for other cases, see Kasule 1970, Kranebitter and Schatz 2002). In our study, P. spinipes and the similarly-sized Algon sphaericollis were observed using their protibia to comb their mouthparts, suggesting that the comb structures present only in L₂ and L₃ larvae may have a cleaning function. comb of bifurcate setae is also present in Arrowinus with the burrowing protibia, but is absent from other Staphylininae with the burrowing protibial type such as Creophilus and the Platydracus group (Fig. 16E). The diverse set of larval leg phenotypes, paralleling the phenotypes of the complete bodies, indicate a frequent recurrence of plesiomorphic traits and morphological parallelisms during the evolutionary. These convergent and reversal characters may lead to a misleading taxonomic conclusions.

The configuration of paratergites and parasternites on abdominal segment I introduces another layer of diversity among Staphylininae larval features, presenting at least four distinct phenotypes, barring atrophy as seen in species of Acylophorus and Atanygnathus. The predominant phenotype resembles the typical structure of paratergites and parasternites found in other abdominal segments but the sclerites are slightly reduced and have fewer setae, observed across various tribes such as Antimerus punctipennis, Quedius brevicornis, Ocypus fulvipennis, Staphylinus erythropterus, and Eucibdelus (Fig. 16J). However, several deviations from this common type exist. For instance, in Saniderus and Arrowinus, while paratergites maintain their usual form, parasternites are reduced to tiny fragments, accompanied by an additional lateral sclerite posteriorly (Fig. 16K). A degree of fusion between these fragmented sclerites determines other observed phenotypes, with examples like Algon sphaericollis, Xanthopygus cognatus, Astrapaeus ulmi, Quedius antipodum and all species of Philonthina, all fragmented sclerites merge to form an U-shaped lateral sclerite (Fig. 16M), while in certain species of Platydracus, including P. tomentosus, P. marmorellus, and P. pseudopaganus pseudopatricius, each paratergite fuses with an additional lateral sclerite, displaying a propensity to bend towards the parasternite (Fig. 16L). Recombination of sclerites is evident at thoracic segments, as seen in Algon sphaericollis, where fusion of additional ventral sclerites occurs notably at segment III of thorax (Fig. 6A, B). This diversity underscores the importance of considering parallel evolution when classifying such phenotypes.

Interestingly, our study falls short of providing suitable genus-level diagnoses. Philonthus and Platydracus appear to be polyphyletic in our trees. We had, nevertheless, observed some genus-specific unusual morphologies:

Eucibdelus, although strongly supported as member of Staphylinina and closely related to Ocypus, differs from other Staphylinini by the wide head with a narrow neck, a shorter pygopod, nasale with 11 teeth, protibia without the comb but with small spines scattered on the anterior face and the presence of frayed setae on all three thoracic segments, among others.

Saniderus shares numerous characters with Platydracus and is nearly indistinguishable from it, particularly when considering eggs and pupae alone. It can be recognized by the trapezoidal head and the paratergites and parasternites of abdominal segment I not fused.

Philonthus spinipes is characteristic by the whip-like urogomphi, a feature absent in other members of phionthina, but present in unrelated Ontholestes, Abemus, and Xanthopygus. P. spinipes differs from other Philonthina by retaining marginal setae on the mala.

Algon sphaericollis differs from other Staphylinini through the notable convergence of paramedian teeth of nasale towards an almost imperceptible median tooth. Additionally, the presence of frayed setae on the meso- and metathorax, but their absence on the prothorax, is a unique trait. A. sphaericollis can be discerned from Staphylinina by the U-shaped lateral sclerites on abdominal segment I, when compared to Philonthina, its protibia features a comb with bifurcate setae.