Why are foodchains short?

It depends on where you start, like:

(1ST)Grass (2ND)Caterpillar (3RD)Snake (4TH)Humans (5TH)Shark (6TH!!!)Worms

In this foodchain Worms is top of the foodchain, it is very strange, you'd think i have gone crazy. But worms eat Sharks when they are dead! They eat them until it is fertlized like soil. Worms eat dead living things- I mean living things that are dead. You might see them cute, but they are actually gross. I don't know how they eat so much when they are so tiny and have a tiny stomach, I also thought Worms live on land, don't they???!!!

Foodchains can be short like mine. But some of them go on and on. Not all of them are short, althought most of them are.