Why a bug? The Metamorphosis

In the beginning of the story, Gregor wakes up as a bug for no apparent reason. If such a transformation can occur without any logic or reason to support it, then what other shapes could Gregor have taken on? Perhaps he could have transformed into a giant duck, only able to communicate with his family through annoying quacks, or maybe Gregor could have become a human-sized lizard where is outward appearance would send his family running in fear. However, I think the reason Kafta chose to change Gregor into a bug was because he wanted to reflect his own personality in the character. After reading a letter published by one of Kafka's friends, Max Brod, I realized that Kafka wrote The Metamorphosis during a time in his life when he was contemplating suicide. Perhaps he felt as if he identified with the bug, being something that people are commonly disgusted at or scared of. He might have also felt the uselessness that Gregor feels in the novel after not being able to work, and he may have related to the fact that many people think of bugs as useless creatures.