Accepted by H. Fery: 18 Mar. 2019; published: 18 Apr. 2019
Licensed under a Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0
ZOOTAXA
ISSN 1175-5326 (print edition)
ISSN
1175-5334
(online edition)
Copyright © 2019 Magnolia Press
Zootaxa 4586 (3): 517
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535
https://www.mapress.com/j/zt/
Article
517
https://doi.org/10.11646/zootaxa.4586.3.8
http://zoobank.org/urn:lsid:zoobank.org:pub:3CFD2CE3-6E93-4DFB-81CB-5406DB34BF2C
The return of the Duke—locality data for Megadytes ducalis Sharp, 1882,
the world's largest diving beetle, with notes on related species
(Coleoptera: Dytiscidae)
LARS HENDRICH
1
, MICHAEL MANUEL
2
& MICHAEL BALKE
1
1
SNSB-Zoologische Staatssammlung, Münchhausenstraße 21, D-81247 München, Germany.
E-mail: hendrich@snsb.de, balke.m@snsb.de
2
Sorbonne Université, Institut de Systématique, Evolution, Biodiversité (ISYEB UMR7205 CNRS MNHN), Case courrier 05, 7 quai St
Bernard, 75 005 Paris, France. E-mail: michael.manuel@upmc.fr
Abstract
Megadytes (Bifurcitus) ducalis Sharp, 1882 is the largest diving beetle in the world and has been considered a candidate
for the world’s rarest insect (Jones 2010). It was described from "Brazil", is only known from the male holotype in the
Natural History Museum (London), and typically thought to be extinct. Here we report the finding of 10 additional spec-
imens, all collected at the end of the 19th century, which were discovered incidentally in different historical collections,
including drawers with unsorted diving beetle accessions of the Muséum National d’Histoire Naturelle (Paris). These
specimens, whilst old, reveal exact locality data for the first time, enabling focused field campaigns to attempt to redis-
cover this giant alive. Locality labels all indicate Santo Antônio da Barra (present name Condeúba), in the southern part
of Bahia, Brazil, suggesting that the species may have a restricted distribution in wetter parts of the Brazilian savanna or
cerrado. We also describe the female of M. ducalis for the first time and present new records of the putatively closely re-
lated species Megadytes magnus Trémouilles & Bachmann, 1980 and M. lherminieri (Guérin-Méneville, 1829), the latter
being recorded for the first time from Ecuador. These three morphologically similar species together form the subgenus
Bifurcitus Brinck, 1945 and we provide photographs of their habitus, median lobes and other morphological details.
Key words: Dytiscidae, Megadytes ducalis, Brazil, cerrado, historical collections, Paris Museum
Introduction
The genus Megadytes Sharp, 1882 is widely distributed throughout the Neotropical region, reaching the Nearctic in
southern Florida (Miller & Bergsten 2016). Megadytes includes 21 species in four subgenera. Fourteen species are
currently reported from Brazil (Blackwelder 1944; Mouchamps 1957; Trémouilles & Bachmann, 1980;
Trémouilles 1989a, 1989b; Ferreira (Jr.) et al. 2006), including Megadytes ducalis Sharp, 1882. With a total length
of around 47 mm, this is the largest species of diving beetle in the world, the second one being the Palearctic
Dytiscus latissimus Linnaeus, 1758 with a length of up to 44 mm. Megadytes ducalis belongs to the subgenus
Bifurcitus Brinck, 1945, together with M. lherminieri (Guérin-Méneville, 1829) and M. magnus Trémouilles &
Bachmann, 1980.
It seems that most Megadytes species are associated with lentic habitats and can be found in heavily vegetated
permanent and temporary water bodies, but detailed habitat requirements for each species remain unknown. Many
species are attracted to light (Miller & Bergsten 2016), and the immature stages of several species have been
described (Cekalovic 1974, 2000; Crespo 1982; Ferreira (Jr.) 1993, 1995; Ferreira (Jr.) et al. 2006; Michat 2006).
Adults and larvae are capable of eating large prey items and attacks on swamp turtles and large frogs have been
reported (Caputo et al. 2006; Oliveira et al. 2013; Zina et al. 2012).
Of all Megadytes species, by far the most mysterious one remains the largest, M. ducalis. Only the male
holotype was known to date, collected before 1882 in "Brazil" and deposited in the Natural History Museum in
London (Trémouilles 1989b; Jones 2010). With no exact locality data and no additional specimens ever sighted,
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this "giant of the Dytiscidae" (Sharp 1882: 714) was listed as "extinct" in the IUCN Red data book (IUCN 2018).
Its huge size, coupled with the lack of other specimens, led Jones (2010) to consider it a candidate for the world's
rarest insect.
Here, we report the discovery of 10 additional specimens with more precise locality data, from historical
collections as well as amongst unsorted historical material in the Muséum National d'Histoire Naturelle, Paris. This
creates for the first time the possibility of a geographically focused research mission to hopefully rediscover the
species alive. We also describe the unknown female of M. ducalis, discuss possible habitat requirements of the
species in light of the locality data, and present additional records of the two other species of Bifurcitus.
Material and methods
A few specimens were cleaned with xylene and examined under a Leica M205C stereomicroscope at
magnifications up to 60×. For examination of the male copulatory apparatus, specimens were relaxed in hot water
for 30 minutes and the genital capsule extracted with strong, pointed forceps with curved tips. The median lobe of
the aedeagus and the parameres were disarticulated and mounted together with the specimen.
Images were taken with a Canon EOS 550D camera fitted with either a 65 mm or MPE65 macro lens, attached
to a Stackshot Macrorail controlled with Zerene Stacker software. Illumination was with two Canon Speedlite
430EX III-RT flashlights and translucent paper diffusors. Images were assembled using Helicon Focus software
and cleaned using Adobe Photoshop CS6 software. The following abbreviations are used in the text: TL (total
length), TL-H (total length without head), and TW (maximum width). Measurements were taken with a digital
calliper "TACKLIFE". Exact label data are cited in quotation marks for all material. Our additional remarks are
provided in square brackets.
Specimen depositories are as follows:
BMNH British Museum Natural History, London
CLH Collection of Lars Hendrich, Munich, Germany, property of NMW
CMM Collection of Michaël Manuel, Paris, France
MNHN-Magasin Muséum National d'Histoire Naturelle (indet. inserenda in boxes of unknown individual
collection association)
MNHN-CG Muséum National d'Histoire Naturelle, Coll. Legros, Paris, France
MNHN-CG Muséum National d'Histoire Naturelle, Coll. Guignot, Paris, France
MNHN-CW Muséum National d'Histoire Naturelle, Coll. Wehncke, Paris, France
MNHN-CR Muséum National d'Histoire Naturelle, Coll. Régimbart, Paris, France
ZSM SNSB-Zoologische Staatssammlung München, Germany
Taxonomy
Genus Megadytes Sharp, 1882
Subgenus Bifurcitus Brinck, 1945
Type species of Megadytes: Dytiscus latus Fabricius, 1801; of Bifurcitus: Cybister giganteus Laporte, 1835.
Diagnosis of subgenus Bifurcitus: Posterior metatibial spur (the narrower one) apically bifid.
Megadytes (Bifurcitus) ducalis Sharp, 1882
Megadytes ducalis Sharp, 1882: 713 (orig. descr.); Zimmermann 1920: 256; Blackwelder 1944: 80.
Megadytes (Bifurcitus) ducalis Sharp, 1882; Brinck 1945: 8; Trémouilles 1989b: 153; Miller & Bergsten 2016: 108; Nilsson &
Hájek 2019: 80.
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FIGURE 1. Habitus in dorsal view of: A) M. ducalis, B) M. lherminieri, C) M. magnus; habitus in ventral view of: D) M.
ducalis, E) M. lherminieri (Ecuador, Esmeraldas), F) M. magnus (Paraguay, Cerro Lambaré).
Type locality. Brazil.
Type material examined. Holotype, male (BMNH): "Brazil, Saunders", "Type", "Megadytes ducalis Sharp".
Other material examined. Brazil: 1 male, 1 female, "San Antônio da Barra [= Condeúba, City Center is at -
14.899° -41.968°, 660 m], Prov. de Bahia, Brésil"; 1 female, "S. Antonia da Barra pr. de Bahia Gounelle
11.12.1888" [printed label]; 1 female, "S. Antonia da Barra pr. De Bahia CH Pujol 1890" [printed label] (MNHN-
CR, drawer 60); 1 female, "Bahia Brésil"; 1 male, "S. Antonia da Barra Pr. de Bahia Gounelle 11.12.1888" [printed
label] (MNHN-CG, drawer 92); 1 male, "Museum Paris Brésil Coll. E. Gounelle 1915" [green printed label]
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[among indet. material in separate drawer]; 1 female, "Brésil Bahia intr" [printed label], "ducalis Sharp"
[handwritten label] (MNHN-CW); 1 female "Cybister giganteus Brésil" [handwritten label]; 1 female, "Museum
Paris Brésil Coll. E. Gounelle 1915" [green printed label], "Megadytes ducalis Shp. San Antonio da Barra"
[handwritten label] (MNHN-Magasin).
Descriptive notes. Large beetle (TL > 42.9 mm) of very robust and "thick" appearance (Fig. 2A). Descriptions
of this species, based on the male holotype, were provided by Sharp (1882) and Trémouilles (1989). Here we
provide photos of the habitus (Figs 1A, D, 2A, 3) and focus on morphological characters of the male in different
views (Figs 7A–E).
FIGURE 2. Habitus in lateral view of: A) M. ducalis, B) M. lherminieri, C) M. magnus.
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FIGURE 3. Female of M. ducalis from collection Régimbart in MNHN [TL = 47.4 mm], the largest known diving beetle
specimen in the world: "San Antônio da Barra, Prov. de Bahia, Brésil".
