Aegus MacLeay, 1819

Genus Aegus MacLeay, 1819 View in CoL (15 spp., 1 ssp.)

1. Aegus chelifer MacLeay, 1819

Distribution: Northern to Southern Vietnam; China including Taiwan (introduction), Laos, Cambodia, Thailand, India?~ Myanmar?, West Malaysia, Singapore, Indonesia including Java, Sumatra, and Kalimantan, Seychelles (introduction).

Remarks: See taxonomic notes by Huang & Chen (2017), Shibata (2023), and Pathomwattananurak & Jiaranaisakul (2024).

1-1. Aegus chelifer chelifer MacLeay, 1810

= Aegus specularis tonkinensis Kriesche, 1921

= Aegus chelifer crassodontus Bomans, 1992

Distribution: Northern to Southern Vietnam; China including Taiwan (introduction), Laos, Cambodia, Thailand, India?~ Myanmar?

2. Aegus rondoni Bomans, 1971

Distribution: Northern to Southern Vietnam; Laos, Thailand.

3. Aegus kumei H. Ikeda, 1997

Distribution: Southern Vietnam.

4. Aegus coomani Didier, 1926

Distribution: Vietnam; China ( Guangxi, Yunnan), Laos.

5. Aegus amplus Nagai, 1994

Distribution: Central Vietnam; Laos, Thailand, Myanmar.

6. Aegus robustus sp. nov.

Distribution: NorthernVietnam.

7. Aegus bidens Möllenkamp, 1902

Distribution: Northern Vietnam.

8. Aegus atricolor Didier, 1928

Distribution: Northern Vietnam.

9. Aegus taurus Boileau, 1899

= Aegus beauchenei Boileau, 1902

= Aegus caprinus Didier, 1928

Distribution: Northern Vietnam; China ( Guangxi, Yunnan, Hainan).

10. Aegus milkintae Bomans, 1992

Distribution: Northern Vietnam.

11. Aegus curvus Didier, 1928

Distribution: Northern Vietnam.

12. Aegus fukiensis Bomans, 1989

Distribution: Northern Vietnam; China ( Fujian, Guangdong, Hunan, Sichuan, Guangxi). 13. Aegus werneri Nagai, 1994

Distribution: Northern Vietnam; China ( Yunnan).

14. Aegus punctulatus Bomans, 1993

Distribution: Northern Vietnam; Laos.

15. Aegus rostratus Didier, 1928

Distribution: Northern Vietnam.

Discussion

Taxonomic studies of Aegus are generally difficult because of the marked species diversity and variation in external morphology among closely related species, with remarkable male polymorphism. The Aegus is by far the largest stag beetle genus ( Schoolmeesters 2025), and there are many undescribed species, including the ones in Vietnam ( Shibata 2023). Moreover, many of the older described species are not accompanied by adequate drawings or photographs, and the morphology of their male genital organs is often ignored in the original descriptions. Thus, there are many problems to solve regarding the systematics of the genus, such as resolving synonyms and publishing proper redescriptions (e.g., Cao et al. 2016; Huang & Chen 2017). Multiple specimens of one taxon are difficult to collect in many Aegus species, except in some common species and subspecies, making their accurate identification and classification more challenging. Here, we examined 16 male specimens of the new species Aegus robustus sp. nov., which revealed intraspecific variation in both external and internal morphological characteristics. Although obtaining females that can unambiguously be assigned to the new species is desirable, our effort reduces certain ambiguities in the Vietnamese Aegus fauna.

Vietnam is a global biodiversity hotspot as part of the Indo– Burma hotspot ( Mittermeier et al. 2011; Marchese 2015). The lucanid fauna is no exception; Vietnam has a very diverse fauna with over 130 species ( Dang & Tran 2003). New species are being added to Vietnam annually, even in 2025 ( Yamamoto & Pham 2025a). Many Aegus species are small, but it was surprising to find a new species, A. robustus sp. nov., with a body length> 4 cm in relatively well-studied Northern Vietnam. Given the species diversity and high proportion of endemism in Aegus , additional Aegus species will be discovered in Vietnam, particularly in less explored Central and Southern Vietnam.

Acknowledgements

We thank Andrei A. Legalov and Vladimir Pešić (Editor- in-Chief) for their helpful comments and efforts to improve our manuscript.

References

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