Crab en Barry Louis Polisar

And then there's the crab,
Who complains bitterly
About how things aren't how
She wants them to be.

She moves very slowly,
Inch upon inch;
With her claws she will paw you
And give you a pinch.

She's crusty, she's crass,
She's also quite rude,
And if she's not careful
She ends up as food