Hynobius boulengeri has a snout to vent length of 79-107 mm and a total length of 144-201 mm. It is a large and robust animal, by far the largest Japanese hynobiid. It has 13, but sometimes only 12, costal grooves. Its hind feet have 5 toes. Its limbs are long and robust, but because of its long trunk, the fore and hind toes have a space of 0.5-3 costal grooves between them when its limbs are adpressed to the flank. The dorsal color of H. boulengeri is bluish black, usually without any patterning, and the ventral surface is lighter. Because of its large size and lack of pattern, H. boulengeri is not easily confused with any other Japanese salamanders (Goris 2004).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Japan
Hynobius boulengeri is found in the mountains of the Kii Peninsula in Honshu, the central mountains in Shikoku, and the Sobo Mountains of Oita Prefecture in Kyushu, living in deciduous broad-leaved, coniferous, or mixed mountain forests on the slopes or bottoms of small valleys (Goris 2004). 
Life History, Abundance, Activity, and Special Behaviors
Hynobius boulengeri breeds from February to the end of May in medium-sized mountain streams, especially near the headwaters. It lays two elongate egg sacs, usually under large rocks. One end of the sacs is attached to the rock and the free end is bent back on itself like a hook. Each clutch contains a total of 17-47 eggs. The larvae have claws which are weakly keratinized and are sometimes absent. Some larvae metamorphose and emerge from August to October of the year of birth, but most remain larvae until the following summer and some until the summer after that. The large overwintering larvae often prey on the next year's batch of new larvae. Juveniles spend the first year or two after metamorphosis on the slopes near the stream of birth, in rock piles or under logs and forest litter. Adults can also be found in such places, but large numbers remain in the stream for many months after breeding, even overwintering there. Others overwinter under rocks and logs, but some can be seen moving on the forest floor on rainy days in December and January. These individuals may begin early breeding in February. Like other Hynobius, H. boulengeri preys on spiders and insects, but it also feeds on a large species of earthworm that grow to 160 mm in length. This worm may be the main sustenance of individuals active in winter (Goris 2004). 
Trends and Threats
The H. boulengeri populations of Kyushu and Honshu are endangered, but it seems that the population of Shikoku is abundant and stable. In Honshu and Kyushu the major threats to this species are the construction of roads and dams and deforestation. This species is protected in Nara Prefecture, Oita Prefecture and Mie Prefecture as a natural monument. (IUCN 2006). 
Relation to Humans
H. boulengeri is kept as a pet. (IUCN 2006). 
Possible reasons for amphibian decline
General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Dams changing river flow and/or covering habitat
Intentional mortality (over-harvesting, pet trade or collecting)
"Odaigahara" is the name of a mountain in Nara Prefecture where the species was first discovered. The genus Pachypalaminus was originally erected for this species on the basis of its having a lacrimal bone in the skull, but it is now known that all Hynobius have a lacrimal bone, so there is no foundation for classifying it as anything other than Hynobius (Goris 2004). 
Nishikawa et al. (2001) demonstrate that the populations on Honshu, Shikoku and Kyushu belong to three separate species, but the formal naming of the populations on Shikoku and Kyushu has not yet been done. Pending this, Hynobius boulengeri is treated as a single species. (IUCN 2006).
Goris, R.C. and Maeda, N. (2004). Guide to the Amphibians and Reptiles of Japan. Krieger Publishing Company, Malabar, Florida.
IUCN, Conservation International, and NatureServe. 2006. Global Amphibian Assessment. < www.globalamphibians.org >. Accessed on 28 November 2006.
Written by Nichole Winters (NicholeWinters AT gmail.com), URAP
First submitted 2006-11-21
Edited by Tate Tunstall (2007-01-16)
Species Account Citation: AmphibiaWeb 2007 Hynobius boulengeri: Odaigahara Salamander <http://amphibiaweb.org/species/3880> University of California, Berkeley, CA, USA. Accessed Mar 18, 2019.
Feedback or comments about this page.
Citation: AmphibiaWeb. 2019. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 18 Mar 2019.
AmphibiaWeb's policy on data use.