In Cookie Clicker, Wrinklers are leech-like creatures that appear during the Grandmapocalypse. They have a 0.0003% chance to spawn per frame, and the chances increase as you go through each stage of the Grandmapocalypse. When a Wrinkler is attached to your cookie, you gain a 5% debuff to your Cookie Per Second, and this stacks as multiple Wrinklers attach to it (up to a maximum of 10, thus 50% debuff). However, they store all the cookies that they have sucked, and when you pop them, you get back 1.1 times the cookies they leeched. In the long run, they actually return more cookies than they take, since none of the cookies they leech are destroyed.

Shiny Wrinklers are a rare version of these creatures that spawn with a small chance and reward you with a bigger amount of cookies when you defeat them. To remove a Wrinkler, simply click on it (multiple times) and it will pop.