Anyone had to deal with maggots before?

[Pizzamorg]

About two weeks ago this fat, brownish worm appeared on my wall with a black end. I assumed it was a maggot and so I killed it and then turned my room upside down to find the source. I was unable to locate a source and I eventually just forgot all about it.

But then I found another one of these things. Same, stumpy, brown wormy thing with a black end - I'm assuming these are maggots very soon to hatching going by a brief Google search but I can't be sure. I'm honestly not sure of a lot of things.

Where are they coming from, for a start? As far as I'm aware there is no food left in my room nor do I get a lot of flies in here, I literally turned my room upside down and with no luck. What is confusing me also is why they are turning up so far apart from one another?