My wizard recently acquired a Staff of Swarming Insects, and I used its Insect Plague spell for the first time. I cast it with the resulting sphere of locusts centered around my character, essentially acting as a (very effective) barrier against some powerful melee-based enemies.
The question came up afterwards, though, whether I used it correctly — as written, the spell damages "each creature" within the sphere, which would technically include my own character. We noticed this because one of the staff's other spells (Insect Cloud) creates a similar but non-damaging effect but specifically states that its effect applies to creatures other than you, something I'd assumed was inherent in these types of spells that give the player control over some type of focused effect.
So is the Insect Plague spell really only useful focused somewhere away from the player character (to avoid damaging themselves), or is the spell's wording just somewhat ambiguous?
Best Answer
The rules as written are fairly clear: it's more typically useful with the caster outside of the sphere.
No exception is given for the caster. The caster was your wizard, which by game rules is "a creature." An object, for example the door next to your wizard, is not a creature and would take no damage.
The spell caster should by a strict ruling have taken damage, mitigated by a save as appropriate. Since this spell requires concentration, if the caster is in it and takes damage a save to avoid losing concentration would also be required.
If the caster just stood there in the Insect Plague, at the end of each turn of being in it the damage is taken again(providing concentration was maintained). It would make sense to roll a save each time for the damage, treating each instance (end of turn) separately. {credit to @yinzanat for that point}
(Citation is from PHB p. 254).