Xylotrupes

Potential Invader

Common name(s)

rhinoceros beetles, elephant beetles

Taxonomy

Family: Scarabaeidae Subfamily: Dynastinae Genus: Xylotrupes

Adult diagnosis

The elephant (or rhinoceros) beetles of the genus Xylotrupes are large scarabs ranging in body length between 30.0–80.0 mm (1.18–3.15 in). Members of the genus are uniformly shiny black in color. Males have large bifurcate horns projecting from both the head and pronotum. Females lack the horns of the male (though sometimes have a weak tubercle) and have a rough, rugose pronotal surface without an anterior fovea. Both sexes lack the acutely produced ocular canthus observed in the related Trypoxylus scarabs; instead, the ocular canthus is rounded or quadrate.

Larval diagnosis

For Xylotrupes ulysses (Bedford, 1974): Grub C-shaped, not hump-backed, cylindrical, cream-colored. Maxilla with galea and lacinia fused or nearly so. Lacinia of maxilla with 3 well-developed unci. Maxillary stridulatory area with 11 or 12 blunt teeth. Left mandible with prominent tooth between molar and scissorial regions. Anterior frontal angle with 3–6 setae. Last antennal segment with 11–18 dorsal sensory spots. Thoracic spiracles pyriform. Legs 4-segmented. Claws each with 3 or four long setae. Raster with teges of 40–80 short, sharp setae, surrounded by longer setae. Lower anal lip with 80–130 short, sharp setae with caudal border of 100–130 longer setae. Anal opening transverse, straight to slightly curved. Plegmatia absent.

Native range

Asia and Australia. Species in the genus Xylotrupes have been recorded from Sri Lanka, India, Nepal, Bhutan, Burma, Indochina, China, the Philippines, Malaysia, Indonesia, Australia, Papua New Guinea, the Solomon Islands, and Vanuatu (Rowland, 2003).

Plant host(s)

Members of this genus feed upon the bark, sap, and flowers of crops such as coconut (Cocos nucifera), cacao (Theobroma cacao) (Bedford, 1975), guava (Psidium guajava) (Firake et al, 2013), and okra (Abelmoschus esculentus) (Nair et al., 2001). They also have been reported feeding upon ornamental plants including hoop pine (Araucaria cunninghamii), rudraksha (Elaeocarpus sphaericus), rainbow eucalyptus (Eucalyptus deglupta), flame tree (Delonix regia), ash (Fraxinus spp.), jacaranda (Jacaranda mimosifolia), raintree (Samanea spp.), and mahogany (Toona australis) (Bedford, 1975).

Life history

Elephant beetle larvae develop in moist humus, rotten wood, or compost. In New Guinea, larvae frequently occur under logs and rotting wood, particularly coconut (Bedford, 1974). In captivity, the egg stage lasted an average of 21 days before larval emergence, the first instar lasted 20 days, the second instar lasted 24 days, and the third instar lasted 144 days (Bedford, 1975). The pre-pupal stage lasted 14 days, with adults emerging from the true pupa after 32 days. Adult females lived 102 days, slightly longer than the 90-day adult lifespan of males. Adults are attracted to lights (Firake et al., 2013) and are likely nocturnal (Bedford, 1975). Adults often congregate at feeding locations where competition for mates takes place (Monteith, 2011).

Pest potential

Minor. While members of this genus are known to feed on commercially important plants, damage is rarely significant (Monteith, 2011). Guava fruits (Firake et al, 2013) and okra pods (Nair et al., 2001) are both recorded as being damaged by Xylotrupes species. These scarabs also cause occasional damage to palms, but reports of elephant beetles severely damaging palm fronds are likely due to misidentification with somewhat similar looking palm pests, the coconut rhinoceros beetle (Oryctes rhinoceros) and Scapanes australis, the Melanesian rhinoceros beetle (Bedford, 1975).

Status in Hawaii

Recorded, not established. This genus has been recorded once in Hawaii. In 1951, a single specimen was collected by a flight attendant in the cabin of a commercial aircraft flying to Honolulu from the Philippines (Hawaiian Entomological Society, 1952B).

Status in Guam

Not established or recorded. There are no records of this genus from Guam.

Potential distribution and dispersal pathway

Species of Xylotrupes are attracted to lights at night (Firake et al., 2013) and could be attracted to well-lit ports and airports. This would allow for hitchhiking on marine or air cargo. Indeed, the specimen recorded in 1951 was found aboard an aircraft. It is worth noting these beetles are popular pets in East Asia (Bouchard, 2014), and intentional transportation may be the most likely means of this species reaching Hawaii or Guam.

Similar species

These massive scarabs are unlikely to be confused with any other beetle recorded from Hawaii or Guam with the exception of the related Japanese rhinoceros beetle (Trypoxylus dichotomus). These scarab beetles may be separated by examining the male head horn (Xylotrupes with horn bifurcate [ending in two points] versus T. dichotomus with horn doubly bifurcate [ending in four points]), ocular canthus in male and female (Xylotrupes with the canthus rounded or quadrate versus T. dichotomus with an acutely produced canthus), and female pronotum (Xylotrupes lacking a fovea versus T. dichotomus with distinct pronotal fovea).

Other names (synonyms)

Scarabaeus gideon (Linnaeus)

Special note

The 1951 specimen was originaly identified as Xylotrupes gideon. However X. gideon has since been split into a number of species, with more than one occuring in the Phillipines. As such it is impossible to make a species level identification for the Hawaiian record without examining the original specimen.

Report your observation

In Hawaii, this members of this genus represents new invasive species. Prevent the spread of this species by reporting your observation at our iNaturalist project.

Xylotrupes ulysses major male; photo by E.L. Engasser

Xylotrupes ulysses major male; photo by E.L. Engasser

Xylotrupes ulysses major male; photo by E.L. Engasser

Xylotrupes ulysses major male; photo by E.L. Engasser

Xylotrupes ulysses major male; photo by E.L. Engasser

Xylotrupes ulysses major male; photo by E.L. Engasser

Xylotrupes ulysses major male; photo by E.L. Engasser

Xylotrupes ulysses major male; photo by E.L. Engasser

Xylotrupes ulysses minor male; photo by E.L. Engasser

Xylotrupes ulysses minor male; photo by E.L. Engasser

Xylotrupes ulysses minor male; photo by E.L. Engasser

Xylotrupes ulysses minor male; photo by E.L. Engasser

Xylotrupes ulysses female; photo by E.L. Engasser

Xylotrupes ulysses female; photo by E.L. Engasser

Xylotrupes ulysses female; photo by E.L. Engasser

Xylotrupes ulysses female; photo by E.L. Engasser

Xylotrupes ulysses male head horn, frontal view; photo by E.L. Engasser

Xylotrupes ulysses male head horn, frontal view; photo by E.L. Engasser

Xylotrupes ulysses male genitalia, caudal view; photo by E.L. Engasser

Xylotrupes ulysses male genitalia, caudal view; photo by E.L. Engasser

Xylotrupes ulysses male genitalia, lateral view; photo by E.L. Engasser

Xylotrupes ulysses male genitalia, lateral view; photo by E.L. Engasser

distribution map for Xylotrupes species

distribution map for Xylotrupes species