The species is endemic to South America and is widespread in the eastern half of the continent.

X. merremii occurs in Venezuela, Guyana, Suriname, French Guiana, Brazil, Bolivia, Paraguay, Uruguay, and northern Argentina.

[4] Other specimens are pale brown dorsally, with broad dark-brown crossbands, which are edged with black, and are narrower or interrupted in the middle.

Like other rear-fanged toad-eaters of the genera Heterodon and Lystrophis, X. merremii uses its enlarged posterior maxillary teeth to puncture and deflate toads which have defensively puffed themselves up, thereby making them easier to swallow.

[4] When threatened, X. merremii raises the anterior part of its body, inflating and spreading its neck, similar to a cobra.