Causus rhombeatus, commonly known as the rhombic night adder, is a species of venomous snake in the subfamily Viperinae of the family Viperidae.

[3] With an average total length (tail included) of 60 cm (24 in), C. rhombeatus is the largest member of the genus Causus.

Northern populations may be patternless,[4] making them difficult to identify, while in others the pale edges may be missing, the rhombic blotches may be a darker color, or there may even be a dark brown vertebral stripe.

[5] Compare this with the description of the common egg-eater Dasypeltis scabra, a species that has a colour pattern and behaviour that may be an evolutionary strategy for defensive mimicry.

[7] C. rhombeatus is found in Sub-Saharan Africa from Nigeria east to Sudan, Ethiopia, Somalia and Kenya, south through Tanzania, Uganda, Rwanda, Burundi, DR Congo, Angola, Zambia, Malawi, Zimbabwe, northern Botswana, Mozambique, Eswatini, and eastern South Africa to Riverdale in the Western Cape Province.

FitzSimons is quoted in Pitman (1938)[8] as saying that, in captivity, some specimens "become so tame that you may allow them to creep, climb and slither round your neck and inside your garments."

[9] Females of C. rhombeatus produce an average clutch of 24 eggs that require a lengthy incubation period of approximately four months.

There have been no modern well-documented cases to back up earlier claims of fatalities due to bites from this species.