Umber hulks are insectoid aberrations that possess the ability to confuse any creature that sees all of their four eyes at once.
Imagine a gorilla with insect shell instead of fur, huge claws and disorienting gaze. Imagine your surprise when your hiding skills prove useless due to the monster's ability to sense the slight tremors you induce on the ground. Imagine the massive creature rushing towards your soft body, frozen in terror.
Imagine yourself safely in your bed instead. The choice is yours.