Use of "mugging up" for hobby

Solution 1:

Yes you can, but I would use "on":

I spent my summer mugging up on butterflies

and it would imply reading everything I could find about them, not going out and looking at them.

The idiom is well-known in Britain. I don't know if it is known elsewhere.

Solution 2:

I don't believe it would make much sense to use it on the context of " I spent my summer's mugging up butterflies" however in the context of "I spent my summers mugging up on the topic of butterflies" Yes... it makes sense.

Mugging up is dervived from the British language and the definition of mugging up is as follows: "Verb: mug up- to cram, grind away, drum, bone up, swot up etc..."