If you find dead maggots or live maggots crawling on your bin, this is usually the result of having had a fly infestation around your bin.
We find that once you have a fly infestation or have found maggots at various stages of their life cycle in your bin, unless you take some action it will be a continual problem.
As previously mentioned in our article on fly infestations, the flies want to lay their eggs in an environment where they can thrive, each maggot that eventually becomes a fly will also lay their eggs in your bin. 
A thorough clean and disinfect usually solves this problem and then there are a several ways to keep your bin from attracting flies in the future to lay more eggs (maggots) on your bin.
If you have a problem with maggots that are knocking you sick and would like a professional clean to get rid of them, you can book a clean here