Trypoxylus dichotomus

Potential Invader

Common name(s)

Japanese rhinoceros beetle, Japanese horned beetle, Japanese elephant beetle

Taxonomy

Family: Scarabaeidae Subfamily: Dynastinae Genus: Trypoxylus Species: Trypoxylus dichotomus (Linnaeus, 1771)

Adult diagnosis

Total body length 40.0–80.0 mm (1.57–3.15 in) including horns. Body shape oblong. Color dull, dark brown to near black. Head of major male with large doubly bifurcate horn (ending in 4 points); minor male with horns reduced; female with 3 tubercles, but lacking horn. Ocular canthus acutely produced in both sexes. Pronotum of male with bifurcate horn; female with distinct fovea, lacking horn.

Larval diagnosis

Undescribed in English. For Dynastinae (Ritcher, 1966): 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 teeth truncate. Legs 4-segmented. Anal opening transverse, straight or slightly curved. Plegmatia absent.

Native range

East Asia. This species is found in Japan, Korea, Taiwan, and China (Bouchard, 2014).

Plant host(s)

Adults of this species feed on the sap of a number of tree species including bao li (Quercus serrata), evergreen ash (Fraxinus griffithii), Mongolian oak (Quercus mongolica), and sawtooth oak (Quercus acutissima) (Hongo, 2006).

Life history

In Japan, adults are active in June and July (Hongo, 2003). Adults congregate at sap flows at night to mate and feed, but if pre-existing flows are not available, then adults may strip bark to create a temporary sap flow (Hongo, 2006). Male competitions for females are well documented, with major males using their horns to attempt to physically pry and flip one another from tree trunk feeding and breeding sites (Hongo, 2003). Eggs are laid in humus, and larvae feed on soil detritus after emerging. Larval development continues until temperatures drop in autumn; winter diapause usually occurs in the final instar. In spring, larvae resume feeding and pupate before emerging as adults (Hongo, 2003).

Pest potential

Minor. Adults preferentially feed upon pre-existing sap flows but may strip bark from trees to create temporary sap flows (Hongo, 2006) causing minor damage. Larvae of this species are not associated with living plants, instead feeding upon soil detritus (Hongo, 2003).

Status in Hawaii

Recorded, not established. This species has been recorded from Oahu (Nishida, 2002) where a single adult male was found alive at Waikiki in 1973 (USDA, 1973). It was suggested that the specimen may have been intentionally brought into Hawaii as a pet (USDA, 1973).

Status in Guam

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

Potential distribution and dispersal pathway

This species is attracted to lights at night and could be attracted to well-lit ports and airports. This would allow for hitchhiking on marine or air cargo. 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

This massive scarab could be confused with the related elephant (or rhinoceros) beetles of the genus Xylotrupes. Trypoxylus dichotomus is separated from Xylotrupes by examining the male head horn (T. dichotomus with horn doubly bifurcate [ending in four points] versus Xylotrupes with horn bifurcate [ending in two points]), ocular canthus in male and female (T. dichotomus with canthus rounded or quadrate, not acutely produced versus Xylotrupes with acutely produced canthus), and female pronotum (T. dichotomus with a distinct fovea versus Xylotrupes lacking a fovea).

Other names (synonyms)

Allomyrina dichotomus (Linnaeus), Scarabaeus dichotomus Linnaeus, Xylotrupes dichotomus (Linnaeus)

Report your observation

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

Trypoxylus dichotomus male; photo by E.L. Engasser

Trypoxylus dichotomus male; photo by E.L. Engasser

Trypoxylus dichotomus male; photo by E.L. Engasser

Trypoxylus dichotomus male; photo by E.L. Engasser

Trypoxylus dichotomus male; photo by E.L. Engasser

Trypoxylus dichotomus male; photo by E.L. Engasser

Trypoxylus dichotomus male; photo by E.L. Engasser

Trypoxylus dichotomus male; photo by E.L. Engasser

Trypoxylus dichotomus female; photo by E.L. Engasser

Trypoxylus dichotomus female; photo by E.L. Engasser

Trypoxylus dichotomus female; photo by E.L. Engasser

Trypoxylus dichotomus female; photo by E.L. Engasser

Trypoxylus dichotomus male head horn, frontal view; photo by E.L. Engasser

Trypoxylus dichotomus male head horn, frontal view; photo by E.L. Engasser

Trypoxylus dichotomus male genitalia, lateral view; photo by E.L. Engasser

Trypoxylus dichotomus male genitalia, lateral view; photo by E.L. Engasser

Trypoxylus dichotomus male genitalia, caudal view; photo by E.L. Engasser

Trypoxylus dichotomus male genitalia, caudal view; photo by E.L. Engasser

distribution map for Trypoxulus dichotomus

distribution map for Trypoxulus dichotomus