Description and life history of a new genus and species of Limacodidae (Lepidoptera, Zygaenoidea) from Taiwan, the first with a monkey-slug-like caterpillar from outside the New World

1 Description and life history of a new genus and species of Limacodidae (Lepidoptera, Zygaenoidea) from Taiwan, the first with a monkey-slug-like caterpillar from outside the New World Yu-Chi Lin1, Rung-Juen Lin2, Marc E. Epstein3 1 Department of Life Science, National Taiwan Normal University, Tingzhou Rd., Taipei 116059, Taiwan 2 Department of Pediatrics and Medical Genetics, National Taiwan University Hospital, Zhongshan S. Rd., Taipei 100226, Taiwan 3 California Department of Food & Agriculture, 3294 Meadowview Rd., Sacramento, CA 95832-1448, USA Corresponding author: Marc E. Epstein (mar[email protected]) Copyright: © Yu-Chi Lin et al. This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International – CC BY 4.0). Research Article Abstract The genus Yufengus gen. nov. is established for a new species of Limacodidae, Y. atrophaneuroides sp. nov. Yufengus is from Taiwan, yet its larva is similar to monkey-slug caterpillars in the New World (Phobetron Hübner, 1825: Limacodidae) in being covered with hairy, detachable tubercles. Monkey-slug caterpillars are currently known to form a monophyletic group which include as many as eight genera in the Americas referred to as the Phobetron complex by Epstein (1996). Although the larva of Yufengus appears, in particular, most similar to the genus Phobetron, a closer look at morphology reveals fundamental differences that are shared with Asian Phrixolepia Butler, 1877. Caterpillars of the new genus are structurally similar to Phrixolepia, but Phrixolepia is more translucent, less hairy, and differs in other characters including those of adults, separated by wing pattern and genitalia. In addition to describing the new genus Yufengus, we explore whether it is indeed in the same clade as the Phobetron complex of genera from the New World. The life history and morphology of adults and immature stages are described in this study. Key words: Detachable tubercles, hag moth, immature, mimicry, monkey slug, Phrixolepia, Yufengus Introduction The slug caterpillar moths (Limacodidae) exhibit a remarkable diversity in larval form. Although all limacodid caterpillars have a slug-like ventral surface, the dorsa are classified into three main types: 1) the “Nettle slug” caterpillar, the most common, is armed with rows of spines; 2) the “Gelatine slug” caterpillar, a non-stinging type of limacodid larvae, has a relatively smooth surface; and 3) the slug caterpillar with fleshy, detachable outgrowths (= tubercles), the rarest, has many fine setae (Dyar 1896, 1907, 1914; Cock et al. 1987; Epstein 1996; Zaspel et al. 2016; Lin et al. 2019). Among the last group, one of the most bizarre and recognizable species is the hairy non-venomous “monkeyslug” caterpillar or “hag moth”, Phobetron pithecium (Smith, 1797), whose fluffy appearance results from its setae-covered detachable tubercles. Academic editor: Erik J. van Nieukerken Received: 11 April 2025 Accepted: 22 May 2025 Published: 21 November 2025 ZooBank: https://zoobank. org/97F0A5BC-0978-4ABE89D5-261193215560 Citation: Lin Y-C, Lin R-J, Epstein ME (2025) Description and life history of a new genus and species of Limacodidae (Lepidoptera, Zygaenoidea) from Taiwan, the first with a monkey-slug-like caterpillar from outside the New World. ZooKeys 1261: 1–15. https://doi.org/10.3897/ zookeys.1261.155406 ZooKeys 1261: 1–15 (2025) DOI: 10.3897/zookeys.1261.155406 2 ZooKeys 1261: 1–15 (2025), DOI: 10.3897/zookeys.1261.155406 Yu-Chi Lin et al.: A new genus of Limacodidae with monkey-slug-like caterpillars The New World genus Isochaetes Dyar, 1899 has similar but translucent tubercles, hence the common name “spun-glass-slug moth”, although other genera occur in both the Neotropics and parts of Asia (Epstein and Corrales 2004; Solovyev and Witt 2009; Lin et al. 2019). New World limacodid genera known to possess detachable tubercles all appear to be in the clade referred to as the Phobetron complex (Epstein 1996): Phobetron Hübner, 1825, Isochaetes Dyar, 1899, Alarodia Möschler, 1886, some species in Euphobetron Dyar, 1905, Vipsophobetron Dyar, 1905, Microphobetron Dyar, 1912, Leucophobetron Dyar, 1897, and Heuretes Grote & Robinson, 1868 (see review of Heuretes, Alarodia, and Leucophobetron in Epstein and Miller 1990). In Asia, Phrixolepia Butler, 1877 and Olona Snellen, 1900 are the only published examples of caterpillars with these detachable tubercles (Solovyev 2009a; Solovyev et al. 2012). The only modern phylogenetic studies of Limacodidae that included more than one genus in the Phobetron complex are those works by Zaspel et al. (2016) and Epstein et al. (in press). Zaspel included Phobetron pithecium (Smith), Isochaetes beutenmuelleri (H. Edwards), Vipsophobetron marisa (Druce), and Alarodia slossoniae (Packard). Epstein et al. includes the same species, except Phobetron hipparchia (Cramer) rather than P. pithecium, and Microphobetron rather than V. marisa. In both studies, the Phobetron complex is a clade among the gelatine caterpillars. This is contrary to Dyar (1899), which had Phobetron as sister to the “spined Eucliids” now referred to as nettles. Curiously, Dyar was aware that Phobetron fed as first instars, unlike the nettles that fast (molt quickly without feeding) in their first instar, but he held the view that these were an early branch of nettles rather than a gelatine (see Zaspel et al. 2016). Lin et al. (2019) indicated that (Phrixolepia + Isochaetes) + “sp. 2” (= Yufengus atrophaneuroides) were a monophyletic group within the gelatine group. Liang et al. (2024), which did not include New World taxa such as Isochaetes, found that Phrixolepia + Pseudidonauton Hering was sister to both the gelatine and nettle clades. Although the position of Phrixolepia + Pseudodinauton is different, this result showing Pseudidonauton to be sister to Phrixolepia suggests that it may be another group with deciduous tubercles. Lin did not describe Yufengus in 2019 because its adults were known only from female samples. The larva and adult morphology of the new genus and species are fundamentally different from others known to have deciduous tubercles from Asia: Phrixolepia, Olona, and Pseudidonauton (Holloway 1986; Cock et al. 1987; Solovyev 2009a, 2009b; Solovyev et al. 2012; Wu et al. 2021). Limacodid diversity in Taiwan is notably high, given the island’s relatively small land area. Over 30 years ago the family was known to be represented by 31 genera and 50 species, as documented by Inoue (1992) in Lepidoptera of Taiwan. Solovyev (2017) added six additional species to the fauna, increasing the total to 43 genera and 58 species. Prior to the addition of Yufengus atrophaneuroides sp. nov., according to the Catalogue of Life in Taiwan website, there were 44 genera and 62 species of Limacodidae recorded in Taiwan (Shao and Chung 2024). Herein, we describe the new species in a new genus as well as its life history with a direction towards future phylogenetic studies that will need more taxon sampling to better understand the evolution of the unique larval characteristics found in Yufengus. This should elucidate whether deciduous tubercles in Asian and New World limacodids are ancestral or independently derived. 3 ZooKeys 1261: 1–15 (2025), DOI: 10.3897/zookeys.1261.155406 Yu-Chi Lin et al.: A new genus of Limacodidae with monkey-slug-like caterpillars Materials and methods Late instars were collected in the field in New Taipei City from their larval host plants, typically on the abaxial surface of mature leaves. Eggs and early instars were obtained from a female that was collected at a mercury light trap in Hualien County. Larvae were reared individually in plastic containers (150 × 75 × 45 mm). Fresh foliage was provided with moist tissue paper to prevent dehydration. The rearing conditions were kept at a constant temperature of 25 °C and 16:8 [L:D] per day. Descriptions of the immature stages and observations on the species’ biology were based on the rearing lot HSU 16C67M, 22B39M, and 22B40M. The rearing lot follows the system of Powell and De Benedictis (1995), where “HSU 22B40M” refers to the name of the rearing database (HSU), the year (22 for 2022), the month (B for February), the sequential number of collection (15), and the taxonomic group (M for moth). Voucher material is deposited in the Department of Life Science, National Taiwan Normal University, Taipei, Taiwan (NTNU). Scanning electron microscopy (SEM) of adult legs and caterpillars was performed with JEOL JSM-5600 scanning electron microscope. Following critical point drying (CPD), we attached the samples to stubs (15 mm diameter) and used a LADD critical-point dryer and coated them with gold palladium using a JEOL JEE-400 Vacuum Evaporator. Wing venation was prepared by first removing wings with micro-scissors and forceps under the microscope. The wings were then moistened with 70% ethanol in a petri dish. A diluted bleach solution (ratio of bleach to water was one to four) was poured into the petri dish to soak the wing set for a few minutes, after which the scales of the wing were removed by a fine brush. Finally, the wing set was fixed in 95% ethanol and then 100% ethanol before being mounted in Euparal and preserved on glass microscope slides. Dissection of the genitalia was performed by first removing the entire abdomen, which was placed in 10% KOH and boiled for 10 min. The abdominal integument and genital capsule stained in a weak solution of Phthalocyanine pigment for an hour, and then transferred to 30% ethanol for cleaning, dissection, and examination. Completed dissections were fixed in 95% ethanol and then 100% ethanol before being mounted in Euparal and preserved on glass microscope slides. Morphological characters follow those in Epstein et al. (in press). Primary types are deposited in the following collections: BMNH The Natural History Museum, London NTNU Department of Biology, National Taiwan Normal University, Taipei Results Yufengus Lin, Lin & Epstein, gen. nov. https://zoobank.org/FCB81D71-7956-4D9F-BAD6-85B9BD7BC7D5 Type species. Yufengus atrophaneuroides sp. nov. (here designated). Diagnosis. No known adults or larvae of Limacodidae from Asia are similar in general appearance to Yufengus. Structurally they are most comparable to Phrixolepia as larvae (Figs 36–39, 52–56) and adults (Figs 57, 58), although adult Phrixolepia forewing lacks the distinct white forewing spots and dark subapical 4 ZooKeys 1261: 1–15 (2025), DOI: 10.3897/zookeys.1261.155406 Yu-Chi Lin et al.: A new genus of Limacodidae with monkey-slug-like caterpillars marking on ventral surface (Figs 9–12), have male filiform (Fig. 15) rather than bipectinate antenna (Fig. 13), have Rs4 originating beyond discal cell (Fig. 18) rather than from discal cell, have gnathos present (Fig. 21) rather than absent, have coiled ductus bursae (Fig. 22) rather than straight, and the labial palp 3rd segment is much shorter compared to 2nd segment compared to Yufengus (Fig. 16) (Note: the description of Yufengus is found below under Y. atrophaneuroides). Etymology. The genus is named after Dr Yu-Feng Hsu, the advisor of the first two authors, who has provided support and encouragement for limacodid studies over the past 10 years. Yufengus atrophaneuroides Lin, Lin & Epstein, sp. nov. https://zoobank.org/D5DB4CBA-9BE3-49B0-BFB8-3749632A3D31 Figs 1–8, 13, 14, 17, 19, 20, 23–34, 41–51 Type materials. Holotype. Taiwan • 1 ♂; New Taipei City, Wulai, Xinfu Rd.; 24.8259, 121.5240; alt. 380 m; 28 Feb. 2022; Y.C. Lin, R. J. Lin, C J. Hung & H. Chang leg.; reared from Oreocnide pedunculata, pupated 21 Mar. 2022, emerged 17 Apr. 2022; HSU 22B39M (Figs 1, 2). Paratypes. Taiwan • 1 ♂; New Taipei City, Wulai, Xinfu Rd.; 24.8259, 121.5240; alt. 380 m; 28 Feb. 2022; Y.C. Lin, R.J. Lin, C.J. Hung & H. Chang leg.; reared from Oreocnide pedunculata, pupated 25 Mar. 2022, emerged 23 Apr. 2022; HSU 22B39M (Figs 7, 8, 13, 14, 17, 19) • 1 ♂; New Taipei City, Wulai, Xinfu Rd.; 24.8259, 121.5240; alt. 380 m; 28 Feb. 2022; Y.C. Lin, R.J. Lin, C.J. Hung & H. Chang leg.; reared from Mussaenda parviflora, pupated 9 Mar. 2022, emerged 31 Mar. 2016; HSU 22B40M (Figs 3, 4) • 1 ♀; New Taipei City, Wulai, Xinxian; 24.8355, 121.5274; alt. 220 m; 31 Mar. 2016; M.X. Luo & H.P. Lu. leg.; reared from Smilax bracteata, emerged 4 May 2016; GenBank: MK128293; HSU 16C67M (Figs 5, 6, 20). Diagnosis. See under Yufengus above. Description. Male (Figs 1–8, 13, 14, 17). Head: frons hairy, brown with yellow scaling; eyes semioval, black; antenna bipectinate from base to apex, medial side of antenna protrusions shorter than the lateral side; labial palpus upcurved with the apex pointing dorsally, covering dark brown scales dorsally and yellow scales ventrally, with the 3rd segment longer than 1/3 of 2nd segment (Fig. 14); proboscis present (Fig. 13). Thorax: dark brown, with long, yellow hairs laterally and posteriorly near abdomen; legs brown, banded with yellow on tarsi (Fig. 7), midleg with one pair of tibial spurs, hindleg with two pairs of tibial spurs, each pair of unequal length (Fig. 8). Forewing: 8.16–8.79 mm long (x –: 8.44 ± 0.32 mm, n = 3). Upperside ground color dark brown, a reddish-brown spot surrounded by black at apex, three black patches on discal cell, discal area, and postdiscal area. Four white spots from inner margin to discal cell (latter two sometimes invisible) (Figs 1, 3), fringe with dark-brown scales. Underside ground color dark brown, broadly pale grey along inner margin, a reddish-brown spot surrounded by black at apex. Forewing venation: Rs2 and Rs3 on common branch originating from Rs1 near discal cell; Rs4 originating from discal cell; MS bisecting discal cell; 1A+2A with basal fork. Hindwing: upperside dark brown; fringe with contrasting pale-yellow scales, becoming mostly black near tornus. Underside similar to upperside. Hindwing venation: 5 ZooKeys 1261: 1–15 (2025), DOI: 10.3897/zookeys.1261.155406 Yu-Chi Lin et al.: A new genus of Limacodidae with monkey-slug-like caterpillars Figures 1–8. Adults of Yufengus atrophaneuroides sp. nov. 1, 2. Male, holotype, HSU 22B39M, upperside and underside; 3, 4. Male, paratype, HSU 22B40M, upperside and underside; 5, 6. Female, paratype, HSU 16C67M, upperside and underside; 7, 8. Male legs, paratype, HSU 22B39M, with scales and without scales (left to right: foreleg to hind leg). Scale bars: 10 mm (1–6), 1 mm (7, 8). 6 ZooKeys 1261: 1–15 (2025), DOI: 10.3897/zookeys.1261.155406 Yu-Chi Lin et al.: A new genus of Limacodidae with monkey-slug-like caterpillars MS present in discal cell; a very short cross vein between R and RS at the proximal third of the wing, inside the discal cell; RS and M1 meet at outer end of discal cell; CuP, 1A+2A, and 3A present as typical in Limacodidae. Abdomen: dark-brown dorsum, yellow in posterior half of ventrum. Female (Figs 5, 6, 50, 51). Similar to male, but larger (forewing 11.14 mm long, from base to apex); antenna filiform; ground color of wing brown, hindwing with a small dark-brown spot at apex, fringe of hindwing brown with dark scales throughout; the 5th tarsomere with a triangular, recessed pad bearing sensilla and spinules (Fig. 51); abdomen brown ventrally. Male genitalia (Fig. 19). Uncus narrow throughout and curved slightly downward at apex. Gnathos absent. Tegumen and vinculum wider than the uncus. Juxta roughly triangular, slightly sclerotized, and setose. Valva elongate, round at apex and with short hairs on inner surface and slightly narrow at base; medial portion with sclerotized process with distal sawteeth. Saccus short. Phallus straight, tubular. Female genitalia (Fig. 20). Papillae anales flat, drop-shaped; anterior apophyses short, digitate, posterior apophyses about two times as long as anterior apophyses. Ductus burse membranous and straight. Corpus bursae ovate, about twothirds length of ductus burse; signum with spines: two large and a few small ones. Figures 9–12. Adults of Phrixolepia inouei; 9, 10. Male, upperside and underside; 11, 12. Female, upperside and underside. Scale bar: 10 mm. 7 ZooKeys 1261: 1–15 (2025), DOI: 10.3897/zookeys.1261.155406 Yu-Chi Lin et al.: A new genus of Limacodidae with monkey-slug-like caterpillars Immature stages (Figs 23–34, 41–49). Egg (Fig. 23): flat oval, 1.92–2.00 mm in long axis (1.97 ± 0.05 mm, n = 3) and 1.22–1.30 mm in short axis (1.26 ± 0.04 mm, n = 3). First instar larva (Fig. 24): yellow ground-colored body with broken orange stripes on mid-dorsum and dorsolateral lines. Prothorax (T1) without tubercles and T2 and T3 each have three tubercles on each side, one D tubercle on A1, two tubercles—D and SD—on A2–A9; each tubercle has three setae. Two L setae on each segment. Early to mid-instar larvae (Figs 25–28): ground color of body yellow to white; some individuals with black patches on the range of T3–A1 and A3–A5 (Fig. 26); some individuals in the stage before the final instar (Fig. 28) with the slightly visible color of the final instar. Final instar larva (Figs 29–32): 12.10–12.48 mm in length (12.3 ± 0.19 mm without spine length, n = 3), 4.93–6.69 mm in width of A3 (5.93 ± 0.9 mm without spine length, n = 3). Head dark brown; labrum with multiple spinules anteriorly and laterally (Fig. 42); stemmata with gaps of approximately the width of a stemma between stemma 1 and stemma 2, and between stemma 5 and stemma 6 (Fig. 43); has only one seta (encircled by stemmata); spinneret brush-like with apex tapered (Fig. 44). Body slug-like, ground color black. Prothorax (T1) white with no tubercles; Figures 13–16. Adult head. 13. Male head of Yufengus atrophaneuroides sp. nov. with only one side of labial palp and small proboscis, paratype, HSU 22B39M; 14. Labial palp without scales of Y. atrophaneuroides sp. nov.; 15. Male head of P. inouei with only one side of labial palp and small proboscis; 16. Labial palp without scales of P. inouei. Scale bar: 1 mm. 8 ZooKeys 1261: 1–15 (2025), DOI: 10.3897/zookeys.1261.155406 Yu-Chi Lin et al.: A new genus of Limacodidae with monkey-slug-like caterpillars mesothorax (T2) with two single black D tubercles, one single black SD tubercle, and two short white L tubercles; metathorax (T3) with a branched D tubercle (two black branched parts on a quadripartite base, Fig. 32), and two single black SD tubercles, and two short white L tubercles. First abdominal segment (A1) with only a branched D tubercle. Abdominal segments with same D tubercles as A2–A8 as A1 but have one single black SD tubercle on each segment, two short white outgrowths for L of A2–A8. The longest D tubercle is on A4 and there are red patches on the tubercle apices of A5–A8, especially distinct on A6 and A7; one long tubercle for D and one white tubercle for L of A9. All tubercles bear numerous plumose setae (Fig. 46) and a single long bristle with tactile function, and those for D and SD can be easily detached when touched. The pretarsal claw of the thoracic leg (Fig. 45) is wide proximally, hook-like distally, with hairlike setae. Cocoon (Figs 33, 34): spheroid, 8.36–6.80 mm in long axis (7.57 ± 0.78 mm, n = 3) and 6.96–5.63 mm in short axis (6.19 ± 0.69 mm, n = 3), brown, with silk blending setae of final instar and forming a thin outer membrane. Pupa (Figs 47–49): thin cuticle, pupal eyepiece with a fracture line, maxilla without maxillary extension, pupal frons rough and shagreened, dorsum of abdominal segments with patch of spicules along anterior margin. Etymology. The specific name atrophaneuroides is derived from the swallowtail genus Atrophaneura Reakirt (Papillionidae) and the Latin suffix -oides, which means “-like”, because the black and red outgrowths of the final instar Figures 17, 18. Wing venation. 17. Yufengus atrophaneuroides sp. nov., paratype, HSU 22B39M; 18. Phrixolepia inouei. Scale bar: 5 mm. 9 ZooKeys 1261: 1–15 (2025), DOI: 10.3897/zookeys.1261.155406 Yu-Chi Lin et al.: A new genus of Limacodidae with monkey-slug-like caterpillars is reminiscent of Atrophaneura larvae. The species epithet is a compound descriptive name comprising an adjective combination with the ending of the second name in masculine form to agree in gender with the generic name. Distribution. Yufengus atrophaneuroides is usually found from montane areas at low altitude in Taiwan. Figures 19–22. Genitalia. 19. Yufengus atrophaneuroides sp. nov., male, paratype, HSU 22B39M; 20. Y. atrophaneuroides sp. nov., female, paratype, HSU 16C67M; 21. Phrixolepia inouei, male; 22. P. inouei, female. Scale bar: 1 mm.