Eight-Legged Nadders are sinuous dragons with eight legs, classified as Cave Dragons. It is implied they may be pack animals, or at least form loose groups. They sleep together closely, and as a result, can actually get tangled up. The resulting 'knot' of Nadders can take days to sort themselves out.
To note, the picture of two Eight-Legged Nadders shows one that appears to have poison glands on the neck. The author frequently draws poison glands or sacs in such a way. However, nothing is mentioned about these Nadders being poisonous.
- The Complete Book of Dragons: Guide To Dragon Species, Cressida Cowell. 2014