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Left: Xylotrupes gideon, adult male. Image by Bernard Dupont, used under Creative Commons Attribution-NonCommercial License. Right: Male X. gideon fighting. Image by Uthen Kamsurin (permission pending)


Table of Contents


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Overview

Below is a guide through my species page. If you're a hardcore beetle lover, or maybe just really bored, you are free to read this page from top to bottom. If not, you may use the flowchart below to help you find the section you're interested in, and click the link in the table of contents to arrive at your desired destination.

Introduction

What is a rhinoceros beetle?

The term rhinoceros beetle, or rhino beetle for short, is commonly used to refer to any kind of horned beetle, and most often refers to species from the subfamily Dynastinae (a majestic and fitting name indeed). The Dynastines are one of the most recognisable groups of beetles, due to their relatively large size and the massive facial horns present in many species (For more diagnostic characters, see As a Species). These signature horns are usually only present in adult males, and often used for macho man-to-man battles for honour and the hands of pretty beetle ladies

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Rhinoceros VS Oryctes rhinoceros. Not to scale, as cool as it would be to have giant beetles roam the earth.Rhinoceros image by Peter Miller, used under Creative Commons Attribution-NonCommercial License. Oryctes rhinoceros image by Sean Yap.

Strength

Rhinoceros beetles are famous for their purported power, with anecdotal accounts of ridiculously impressive feats strength. An entry in the Guinness Book of World Records claims that the strongest animal was a rhinoceros beetle that could support 850 times its body mass

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Footnote Macro

Matthews, P. (1992). The Guinness Book of World Records. Enfield, UK: Guinness Publishing Ltd.

, permission pending.

VS Stag beetles

Quite often, rhinoceros beetles are confused with stag beetles (Family Lucanidae) by the layperson, as both are usually portrayed with large horn/antler-like head ornaments used for fighting. However, the grappling ornaments (antlers) of stag beetles are their enlarged mandibles (mouthparts), while the rhino beetles employ the use of their facial and thoracic horns in combat, and do not use their mouths to fight (which is admittedly a lot less gross). Because the rhino beetle horns and stag beetle antlers move along perpendicular planes, they happen to interlock nicely when facing off against each other, rhino and stag beetles are often pitted against each other in the popular japanese beetle fights. Another noticeable difference between the two - while rhino beetles have deeper, rounder bodies like sausages, stag beetles are dorsoventrally flattened like pancakes. These differences are denoted in the pictures below.

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Comparison between Xylotrupes gideon and Aegus parallelus, a native stag beetle. Xylotrupes gideon images by Sean Yap.A. parallelus images by John Ska (lateral view) and Udo Schmidt (dorsal view), used under Creative Commons Atribution-Share Alike License.

As Warriors

Rhinoceros beetles are also famous for their fighting ability. In Japan, rhino beetles are known as 'kabutomushi', which when translated means 'helmet bug', supposedly from the way the beetles' horns resemble the ornaments on samurai helmets (kabuto).

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Some samurai helmets, especially the 'kawari kabuto' (strange helmet), were elaborately shaped with large ornaments such as horns.Image by Ian Armstrong, used under Creative Commons Atribution-Share Alike License.

Mating

Female rhino beetles are sexy and they know it, and they usually just sit atop trees, wafting their pheromones to get the boys to come to them. More often than not, multiple guys will be attracted to a single female, and they land on a tree, ascending in search of her. This becomes a battle to the top, and males that encounter each other on the tree grapple each other and engage in wrestling matches, in which the loser is lifted off the tree and tossed to the bottom, having to start his climb from scratch.

If beetle horns and size are so important in getting to reproduce, one would expect only the largest and strongest males to survive, but reality is never as we expect. The brown rhinoceros beetles have male morphs that vary a lot in size of both the body and the horns, where smaller males have correspondingly smaller horns. But how do these pretty boys get around the alpha males and get to pass on their genes such that small size remains in the gene pool?

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 have proposed the possibility of sneak mating, where effeminate males fool the buff alpha males into thinking that they're female, thus getting around them without direct confrontation (in which they would most certainly lose) in order to mate with the actual females - with the large males none the wiser!

Beetle fighting

In Thailand, the brown rhino beetle is known as 'Kwang', and betting on beetle fights is a popular past time, especially among men. The sport has recently been outlawed in the state

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Selecting the best fighters for battle. Video by Daniel Ambuehl, obtained from YouTube under Fair Use guidelines.

As Pets

Beetle breeding is big business, especially in Japan and Thailand, where beetles are not only used for fighting but also often kept as pets. Some individual beetles can even be sold for as much as a thousand USD!

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Before embarking on a journey with your pet beetle, one should first understand the life cycle of the beetle.

Life cycle

As a beetle, rhino beetles undergo complete metamorphosis

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Life cycle of X. gideon. Images by Alessandro Siletto (egg), Rachael Moore (grub), JC Shou (pupa), Lai Wagtail (adult).Used under Creative Commons Attribution - Non Commercial License.

As Food

Entomophagy is the sciencey word for eating bugs, and this new trend is taking the world by storm.
In Laos and Thailand, Xylotrupes gideon is one of the species that is eaten by locals, both grubs and adults. It is known as 'Maeng kee noon' in Thai, and 'Mang kwang' in Lao . In Thailand, the beetles are usually wok-fried and seasoned with sauce and pepper powder, to be consumed as a snack food on its own or with beer.

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Interestingly, in areas such as plantations where X. gideon has become a pest species, local tribes have been encouraged to eat them as a possible way of controling the beetle population (Wongdao & Black, 1987).

As Pests

Throughout their range, X. gideon is a known pest species that targets palms such as coconut, but sometimes also goes for the bark of fruit trees (Wongdao & Black, 1987).
It is known to feed on newly opened coconut inflorescences and the undersurface of frond midribs, causing the distal portion to break and hang down, affecting the survivability of coconut trees

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, apples and pears (Wongdao & Black, 1987). It is generally regarded as a minor pest though, and is not feared as strongly as its cousin, Oryctes rhinoceros.

As Pop Culture Icons

Japan is crazy about insects, particularly beetles, and a popular trope in television and gaming series and franchises is the 'Japanese Beetle Brothers' trope, where characters designed to resemble rhinoceros beetles and stag beetles are often portrayed as allies or rivals.

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Kabuto and Gatack from the Kamen Rider Kabuto series by Toei, used in accordance with Fair Use guidelines.

As a Species

The Brown rhinoceros beetle (Xylotrupes gideon)

Appearance

Like its common namesake, this species is largely brown colour, though variation exists between individuals, with some so dark they look almost black. The elytra (hardened forewings that protect the flight hindwings) are relatively smooth and without punctures. These are large beetles, with sizes ranging from about 35 - 70mm for most individuals

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Adult male major and minor Xylotrupes gideon to scale. Major is 60mm in length, minor is 38mm. Image by Sean Yap, specimen collected by Max Khoo De Yuan.

Type Specimen

The type specimen for Xylotrupes gideon resides in the Linnaean Collections of the Linnaean Society of London. It is a male individual labelled with the basiosynonym name, Scarabaeus gideon. The label suffers from a real information deficit. Also, the poor specimen appears to have lost his head.

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Holotype for the species Xylotrupes gideon. Images from the Linnaean Society of London, pending permission.

How to identify - diagnosis

Xylotrupes species are pretty difficult to tell apart from external morphology, and often dissection of genetalia is required.
The raspula is a sclerotized piece in the internal sac of the male genitalia of a beetle. The position of this part of the genatilia is shown in the diagram below.

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Variation in raspular shape within the Xylotrupes genus. Image adapted from Rowland, 2003 (permision pending)

In Singapore

Xylotrupes gideon is found throughout Southeast Asia, including Singapore. In Singapore, this species is easily recognisable as one of our largest beetles, and the largest horned species. The only other horned dynastine beetle in Singapore is Oryctes rhinoceros, which is a basically a smaller, less impressive cousin of X. gideon.

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The main difference to look out for is the two-pronged facial (cephalic) and thoracic horns, which together are a character only seen in Xylotrupes species. This also works for the minor Xylotrupes males, which have smaller horns but that are still two-pronged.

Distribution

Xylotrupes gideon can be found throughout South and Southeast Asia, as well as northern Oceania.

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Map showing records of X. gideon in South and Southeast Asia and Oceania. Map ©Designed by The Polistes Corporation, records from the Global Biodiversity Information Facility.

Habitat

Xylotrupes gideon is usually found in forested areas, as well as in palm plantations where it is considered a pest

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. (For more detail, jump to As a Pest)
In Singapore, this species is now relatively uncommon, and sightings are sporadic and random. They sometimes end up in peoples' homes at night, attracted by artificial lighting.

Classification

Warning: Here onwards is where things get pretty technical.
Xylotrupes gideon was first described by Linnaeus in 1767 as Scarabaeus gideon, before Hope established Xylotrupes as a genus in 1837 with Scarabaeus gideon as the type

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. Xylotrupes was one of the 10 recognised genera from the Dynastini tribe in Endrodi (1985), but has since been determined to be inadequately diagnosed and has been re-diagnosed in 2003 by Rowland.

The genus Xylotrupes can be differentiated from other members of tribe Dynastini via its unique apomorph of the constitution of the right raspula as a single large spine [cite Rowland]. Also, only Xylotrupes has the following character combination in this tribe: Apically bifurcate pronotal and cephalic horns, with the pronotal horn the same size or longer than the cephalic horn in major males.

The higher classifications, synonyms and subspecies of Xylotrupes gideon according to the latest revision by Rowland are listed below.

Higher Classification

- Kingdom Animalia (Animals)
- Phylum Arthropoda (Arthropods)
- Subphylum Hexapoda (Hexapods)
- Class Insecta (Insects)
- Order Coleoptera (Beetles)
- Suborder Polyphaga (Water, Rove, Scarab, Long-horned, Leaf and Snout Beetles)
- Superfamily Scarabaeoidea (Scarab, Stag and Bess Beetles)
- Family Scarabaeidae (Scarab Beetles)
- Subfamily Dynastinae (Rhinoceros Beetles)
- Tribe Dynastini
- Genus Xylotrupes
- Species gideon

Synonyms

Sometimes, different names are assigned to the same species. This usually happens when a scientist describes a species that has already been described earlier, perhaps unaware of the existing name, or mistaking a morphological variant within the species as a new species. In such a case, the earlier name is treated as the accepted senior synonym, while all names that come after it are considered junior synonyms and generally should not be used. Synonyms can also be the original name of the species when it was first described, that may no longer be correct to use if the species has been transferred to another genus afterwards. This is that case with the nameScarabaeus gideon, the name that Linnaeus first gave the species when it was described in 1767. Since the species has been transferred to the genusXylotrupes, the nameScarabaeus gideonshould no longer be used.

Xylotrupes gideonis a species with a relatively large number of synonyms. This is partly due to the fact that it was also known by the genusScarabaeusfor about 70 years, a time span that allowed for the creation of numerous synonyms under that genus name. This list ofScarabaeussynonyms add on to the list of synonyms under the genusXylotrupes.Xylotrupes gideonis also a relatively charismatic species with many interactions with humans as pests or as a part of local culture, and is likely to get much attention from beetle workers. This, coupled with the fact that some subspecies ofX. gideonshow significant intraspecific morphological variation

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, especially between males, could have lead to higher frequency of workers wrongly describingX. gideonindividuals as new species. A list of synonyms for this species is listed below.

Scarabaeus gideonLinnaeus 1767
S. oromedonDrury 1770
S. phorbantaOlivier 1789
Geotrupes dentatusWever 1801
S. ScorticumVoets 1806
S. simsonVoets 1806
S. nimrodVoets 1806
S. furcigerVoets 1806
S. alcibiadesDejean 1833
Xylotrupes beckeriSchaufuss 1885
X. beckerivar.metzeneriSchaufus 1887
X. inarmatusSternberg 1906
X. gideon gideonMinck 1920
X. sumatrensisMinck 1920
X. borneensisMinck 1920
X. bourginiPaulian 1945
X. gideon beckeriEndrodi 1951
X. gideon sumatrensisEndrodi 1951
X. gideon borneensisEndrodi 1951

Subspecies

While different websites have different lists of X. gideon subspecies, Rowland asserts that material of this widespread species has not yet been sufficiently examined to support a comprehensive subspecific classification. In Singapore, the local subspecies is likely to be Xylotrupes gideon beckeri (Rowland, 2003).

Phylogeny

Phylogeny within Xylotrupes

A phylogenetic study of the genus Xylotrupes exists, taking into account only morphological characters (Rowland, 2003). Characters used in the construction of this phylogeny include the length of pronotal (thoracic) horn relative to the cephalic (face) horn, the position of the cephalic horn tooth, number of mandibular teeth, and raspula shape. The tree below was obtained, showing the proposed relationship between X. gideon and other species from the genus Xylotrupes, with a Trypoxylus species as the outgroup as Trypoxylus has been found to be the sister group to Xylotrupes.

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Rowland's phylogenetic analysis shows that only two apomorphs (derived characters), both in the raspula, distinguish Xylotrupes from other dynastine genera. The assumed monophyly of the genus however, is supported by the combination of other characters.

Phylogeny within tribe Dynastini

Rowland and Miller have more recently presented the first inclusive phylogenetic analysis of the Dynastini tribe of giant rhinoceros beetles, which contains the genus Xylotrupes

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On the left is the single most parsimonious cladogram resulting from analysis of morphological and molecular data, while a summary tree is shown on the right.Numbers immediately above hashmarks are morphological character numbers. Numbers below hashmarks are character state numbers derived on that branch. Numbers in bold above branches are bootstrap support values. Inset branching diagram is single most parsimonious cladogram from analysis of all data with branch lengths proportionate to number of character state transformations mapped using “fast” optimization. From Rowland and Miller, pending permission from the authors.

The trees show that the genus Xylotrupes is sister to Allomyrina, a genus of japanese rhinoceros beetles. This group, is in turn sister to a group containing Trypoxylus (also a japanese rhinoceros beetle) and Xyloscaptes. This is an interesting result, as in terms of horn morphology, Xylotrupes is more similar to Xyloscaptes while Allomyrina and Trypoxylus// look almost identical, but the groupings show a relationship differing from expectations. In any case, the four genera are well-supported as monophyletic, with Rowland and Miller proposing recognition of Xylotrupina as a valid subtribe.

References

Display Footnotes Macro

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This page was authored by Sean Yap

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