The first description of the species emerged in a study of morphological variation of the widespread species Pseudechis australis, known as the king brown or mulga snake. The author, Laurie Smith, examined a large series of specimens, allocating 213 to P. australisand 21 to the new species. The holotype is a female specimen, carrying eggs, collected at the Yalgoo region in 1963 by I. C. Carnaby. The suggestion of a cryptic Pseudechis species in the midwest was noticed by Ludwig Glauert in 1957, but with few available specimens the author hesitated to describe it as a new taxon. The morphological comparison by Smith concluded the closest affinity was with the type of the genus, P. porphyriacus, the red-bellied Pseudechis of Australia's eastern states. A revision of the phylogeny of 'black snake' genus several years later found instead that this species was most closely related to P. australis in finer details of morphology, a position supported by comparison of results from electrophoretic analysis of blood proteins and phylogenetic indicators. Common names for P. butleri include Butler's black snake, Butler's snake, and spotted mulga snake. The generic name, Pseudechis, suggests a similarity to the African-Asian vipers of the genus Echis. The specific epithet, butleri, commemorates the conservation efforts of naturalist W. H. "Harry" Butler.
Description
A species of Pseudechis, a genus of large front-fanged venomous snakes occurring in Australia and New Guinea. The species is similar to the common mulga P. australis, a larger and widespread snake which occurs in sympatry at parts of central Western Australia. However, Pseudechis butleri is spotted with yellow or yellow-green scales and does not usually exceed a total length of 1.6 metres. The snout to vent length is up to 1.56 metres, the tail's length is around 15% of the SVL. The dorsal scales of the body are occasionally all black, but most of the upper body is covered in yellow or brownish scales with black bases. The colour of the head and neck tends to completely black. The neck is slightly defined by the species head, broad and slightly larger the robust body. Pseudechis butleri is readily distinguished from others of the genus, by coloration and number of scales at the ventral side. The number of scale rows at the midbody is 17, at the neck this is usually 19, but ranges from 16 to 23, and 17 rows at the tail. Pseudechis australis has reddish-brown scales with a creamy coloured edge on the lower part of the body, whereas this species has black-based scales with bright yellow. The number of ventral scales is also less than specimens of P. australis found at the same latitude, 204–216 compared to the range 189–207 for P. butleri. The yellow colour of ventral scales is pink or red in the black snake of Eastern Australia, Pseudechis porphyriacus, which also fewer scales than this species. The lighter spots of this species was described by Glauert, when examining a recently killed specimen, as "primrose yellow".
The venom of P. butleri contains systemic myotoxins. Treatment for positive envenomation is the same as for P. australis, using a black snake antivenom.
