The Bandersnatch is a fictional creature mentioned in Lewis Carroll's poem "Jabberwocky". The form or size of the creature is not described. Nor is it clear whether the Bandersnatch is a singularity, like the Phoenix.

The only description given of it is that the hero should "shun the frumious Bandersnatch." Other advice given to the beamish hero proving quite accurate, one must dismiss the possibility that the speaker within the poem was uninformed about the Bandersnatch, which however does not actually make an appearance in "Jabberwocky". Thus it is clear that the Bandersnatch is not of a size or character to be embraced. Elsewhere in Through the Looking-Glass, however, it is implied (but not stated) that a Bandersnatch is quick-moving, and that there may be more than one of it: "She runs so fearfully quick. You might as well try to catch a Bandersnatch!"

It is not stated whether there are non-frumious Bandersnatches, or whether these can be approached safely, merely that the hero of the poem must shun a Bandersnatch that is frumious. At the same time, it may be that 'frumious' is not a merely descriptive adjective, but a definitive one, describing the essential quality of the Bandersnatch. It should be noted that a Google search of 'frumious' inevitably brings up 'Bandersnatch', and, conversely, no Bandersnatch can be googled without its frumiousness being mentioned.

Fortunately, Carroll's "The Hunting of the Snark" (Fit the Seventh) settles some of these questions: in an encounter with a bandersnatch it is described as moving swiftly, having a neck it can extend, and having snapping, frumious jaws, which with it tries to grab the Banker.

In Larry Niven's fictional Known Space universe, the Bandersnatchi are colossal sluglike creatures. They were created by the Tnuctipun, used by the Thrintun as genetic engineers, as a food source by the Thrintun. Unknown to the Thrintun, the Bandersnatchi were created sentient, as spies, and immune to telepathy. They are also immune to radiation as their chromosomes are the thickness of a human thumb. Their sentience is largely related to the size of their massive brains, which were considered desirable by the Thrintun because of their delicious flavor.

In the futuristic role-playing game Shadowrun, the bandersnatch is a monster which is hard to catch (or avoid!) because it has active camouflage. The rule book (ISBN 1555601235) in which the bandersnatch appears is putatively a reference work from the future, incorporating marginalia in a form similar to Wikipedia talk pages. The marginalia for the bandersnatch entry note its similarity to a creature which appeared in an old movie starring "Senator Schwarzenegger" — clearly implying Predator. This reflects the Jungian flavour of Shadowrun, in that many paranormal phenomena seem to be created out of the symbols in the subconscious of the culture in which they are found. Interestingly, this book was published in 1990, more than a decade before Governor Arnold Schwarzenegger had entered politics.