Metamorphosis Book by Franz Kafka

The story begins with a traveling salesman, Gregor Samsa, waking to find himself transformed (metamorphosed) into a large, monstrous insect-like creature.

The cause of Gregor's transformation is never revealed, and Kafka himself never gave an explanation.

The rest of Kafka's novella deals with Gregor's attempts to adjust to his new condition as he deals with being burdensome to his parents and sister, who are repelled by the horrible, verminous creature Gregor has become.