Answer:
When they are caught, they are thrown away. When they escape, you itch all day.
Long and slinky like a trout, never sings till it's guts come out.
Two bodies have I, though both joined in one. The more still I stand, the quicker I run.
A horrid monster hides from the day, with many legs and many eyes. With silver chains it catches prey. And eats it all before it dies. Yet in every cottage does it stay. And every castle beneath the sky.
My first half is normally made of stone, my second is crazy, and I taste sweet when complete.
I have two eyes in the front and a lot of eyes on my tail