Trypoxylus dichotomus

Status

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)

DNA barcode

none available

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 bifurcatebifurcate:
a process dividing into two points
horn (ending in 4 points); minor male with horns reduced; female with 3 tubercles, but lacking horn. Ocular canthuscanthus:
a process extending over and sometimes dividing the eye
acutely produced in both sexes. Pronotumpronotum:
the dorsal surface of the thorax
of male with bifurcatebifurcate:
a process dividing into two points
horn; female with distinct foveafovea:
a depressed pit or indentation
, lacking horn.

Larval diagnosis

Undescribed in English. For Dynastinae (Ritcher, 1966Ritcher, 1966:
Ritcher P. 1966. White grubs and their allies: a study of North American scarabaeoid larvae. Oregon State University Monographs, Studies in Entomology 4: 1-219.): Grub C-shaped, not hump-backed, cylindrical, cream-colored. Maxillamaxilla:
set of paired mouthparts located posterior to the mandibles
with galeagalea:
outer branch or lobe of the maxilla
and lacinialacinia:
inner portion of the maxilla
fused or nearly so. Lacinialacinia:
inner portion of the maxilla
of maxillamaxilla:
set of paired mouthparts located posterior to the mandibles
with 3 well-developed unciunci:
in scarab larvae, a hooked process on the distal margin of the maxilla
. Maxillary stridulatory teeth truncatetruncate:
appearing cut-off or suddenly shortened
. Legs 4-segmented. Anal opening transversetransverse:
extending horizontally across a surface
, straight or slightly curved. PlegmatiaPlegmatia:
in scarab larvae, a paired, lateral region with a somewhat sclerotized surface bordered by marginal spines with acanthoparia
absent.

Native range

East Asia. This species is found in Japan, Korea, Taiwan, and China (Bouchard, 2014Bouchard, 2014:
Bouchard P. 2014. The Book of Beetles. Chicago, IL: University of Chicago Press.).

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, 2006Hongo, 2006:
Hongo Y. 2006. Bark carving behavior of the Japanese horned beetle Trypoxylus dichotomus septentrionalis (Coleoptera: Scarabaeidae). Journal of Ethology 24: 201-204. full text (accessed 2015)).

Life history

In Japan, adults are active in June and July (Hongo, 2003Hongo, 2003:
Hongo Y. 2003. Appraising behavior during male-male interaction in the Japanese horned beetle Trypoxylus dichotomus septentrionalis (Kono). Behavior 140: 501-517. full text (accessed 2015)). 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 flowsap flow:
a plant wound resulting in sap flowing (bleeding) to the plants surface
(Hongo, 2006Hongo, 2006:
Hongo Y. 2006. Bark carving behavior of the Japanese horned beetle Trypoxylus dichotomus septentrionalis (Coleoptera: Scarabaeidae). Journal of Ethology 24: 201-204. full text (accessed 2015)). 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, 2003Hongo, 2003:
Hongo Y. 2003. Appraising behavior during male-male interaction in the Japanese horned beetle Trypoxylus dichotomus septentrionalis (Kono). Behavior 140: 501-517. full text (accessed 2015)). Eggs are laid in humushumus:
soil rich in organic matter
, and larvaelarvae:
the immature form of an insect; in scarabs, also called grub or white grub; preceded by the egg stage, followed by the pupal stage
feed on soil detritusdetritus:
organic debris; particularly plant debris
after emerging. Larval development continues until temperatures drop in autumn; winter diapausediapause:
a period of biological inactivity, or dormancy, sometimes called hibernation
usually occurs in the final instarinstar:
in scarabs, one of the three larval growth phases (i.e., first instar, second instar, third instar), each ending with the larvae molting to the next phase
. In spring, larvaelarvae:
the immature form of an insect; in scarabs, also called grub or white grub; preceded by the egg stage, followed by the pupal stage
resume feeding and pupate before emerging as adults (Hongo, 2003Hongo, 2003:
Hongo Y. 2003. Appraising behavior during male-male interaction in the Japanese horned beetle Trypoxylus dichotomus septentrionalis (Kono). Behavior 140: 501-517. full text (accessed 2015)).

Pest potential

Minor. Adults preferentially feed upon pre-existing sap flows but may strip bark from trees to create temporary sap flows (Hongo, 2006Hongo, 2006:
Hongo Y. 2006. Bark carving behavior of the Japanese horned beetle Trypoxylus dichotomus septentrionalis (Coleoptera: Scarabaeidae). Journal of Ethology 24: 201-204. full text (accessed 2015)) causing minor damage. LarvaeLarvae:
the immature form of an insect; in scarabs, also called grub or white grub; preceded by the egg stage, followed by the pupal stage
of this species are not associated with living plants, instead feeding upon soil detritusdetritus:
organic debris; particularly plant debris
(Hongo, 2003Hongo, 2003:
Hongo Y. 2003. Appraising behavior during male-male interaction in the Japanese horned beetle Trypoxylus dichotomus septentrionalis (Kono). Behavior 140: 501-517. full text (accessed 2015)).

Status in Hawaii

Recorded, not established. This species has been recorded from Oahu (Nishida, 2002Nishida, 2002:
Nishida G (editor). 2002. Hawaiian terrestrial arthropod checklist, fourth edition. Bishop Museum Technical Report 22: 1-313.) where a single adult male was found alive at Waikiki in 1973 (USDA, 1973USDA, 1973:
Anonymous. 1973. Hawaii insect report. Cooperative Economic Insect Report issued by Plant Protection and Quarantine Programs, US Department of Agriculture 23: 676.). It was suggested that the specimen may have been intentionally brought into Hawaii as a pet (USDA, 1973USDA, 1973:
Anonymous. 1973. Hawaii insect report. Cooperative Economic Insect Report issued by Plant Protection and Quarantine Programs, US Department of Agriculture 23: 676.).

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, 2014Bouchard, 2014:
Bouchard P. 2014. The Book of Beetles. Chicago, IL: University of Chicago Press.), 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 bifurcatebifurcate:
a process dividing into two points
[ending in four points] versus Xylotrupes with horn bifurcatebifurcate:
a process dividing into two points
[ending in two points]), ocular canthuscanthus:
a process extending over and sometimes dividing the eye
in male and female (T. dichotomus with canthuscanthus:
a process extending over and sometimes dividing the eye
rounded or quadratequadrate:
square-like in shape
, not acutely produced versus Xylotrupes with acutely produced canthuscanthus:
a process extending over and sometimes dividing the eye
), and female pronotumpronotum:
the dorsal surface of the thorax
(T. dichotomus with a distinct foveafovea:
a depressed pit or indentation
versus Xylotrupes lacking a foveafovea:
a depressed pit or indentation
).

Other names (synonyms)

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

Report your observation

In Hawaii, this species represents a new invasiveinvasive:
a species that has recently arrived to a new location, usually via human activity, causing notable economic and/or ecological damage
species. Prevent the spread of this species by reporting your observation at our iNaturalist project.