Can purple worms poison themselves?

[Chaos_Laicosin]

Probably a dumb question here, but can purple worms poison themselves? The MM does not say they are immune to poison and they are a (basically) blind, Int 1 monster. So would getting in close or grappling it with the intent of dodging a stinger attack so it hits itself be a viable strategy? Or is there a general rule somewhere that states all monsters are immune to their own poison even if they aren't immune to poisons in general?

[MaxWilson]

Probably a dumb question here, but can purple worms poison themselves? The MM does not say they are immune to poison and they are a (basically) blind, Int 1 monster. So would getting in close or grappling it with the intent of dodging a stinger attack so it hits itself be a viable strategy? Or is there a general rule somewhere that states all monsters are immune to their own poison even if they aren't immune to poisons in general?

There is no such rule stating that monsters are immune to their own poison. However, Purple Worms are not blind, they just have blindsight (meaning that they can still "see" by smell/hearing/etc. even when they are blinded), so this should be harder to do to a Purple Worm than to e.g. a cobra or a giant scorpion, not easier.

But you could totally use Purple Worm poison to kill more Purple Worms.

[Amnestic]

I don't think it'd be reasonable to try to use positioning to 'trick' the purple worm into hitting itself. That's the sort of critical fumble shenanigans you don't really want the DM to open up against the players.

If you wanted to try to grapple and then strength check to turn its own stinger on itself...I'd consider letting you try that! Would require probably an opposed strength check (maybe athletics, but probably not), potentially at disadvantage because you're trying to aim it at itself. I might consider making it resistant to its own poison too, since that feels 'correct' even though it's not explicitly stated.

[NaughtyTiger]

An urban legend growing up was that you could trick a scorpion into stinging itself if you poked it in the back...
If a player referenced something like that as reference for tricking a purple worm, maybe in conjunction with illusion, then I would allow it.

[MaxWilson]

I don't think it'd be reasonable to try to use positioning to 'trick' the purple worm into hitting itself. That's the sort of critical fumble shenanigans you don't really want the DM to open up against the players.

Unless you have a meta-rule along the lines of "crazy stuff works if it's entertaining, but only the first time. On the second and subsequent attempts, the initial success will turn out to have been a fluke."