This spell transforms a creature that you can see within range into a new form. Unwilling targets must make a Wis saving throw to avoid the effect. Shapechangers and targets that have 0 hit points are unaffected by this spell.
The transformation lasts for the duration, or until the target drops to 0 HP or dies. The new form can be any beast whose challenge rating is equal to or less than the target's (or the target's level). The target's game stats, including mental ability scores and HP, are replaced by the stats of the chosen beast. It retains its alignment and personality. When it reverts to its normal form, the creature returns to the number of HP it had before it transformed.
The creature is limited in the actions it can perform by the nature of its new form, and it can't speak, cast spells, or take any other action that requires hands or speech. The target's gear melds into the new form. The creature can't activate, use, wield, or otherwise benefit from any of its equipment. See PHB for full details.
a caterpillar cocoon