Well, in general, I try to find the thing that makes a game fun, and really focus on that for the jam. For example, in my game, through playtesting, I tried to make sure that the player could buy at least one upgrade after every run. I don't think I quite hit the mark, but I tried to highlight what I thought would be the most fun 'moment' in the game and give it to the player as quickly and as frequently as possible.
To that note: in your game, having a giant swarm devour stuff is just fun to watch. In that respect, it shares a lot with a demonstration as well as a game. So, could you pull any ideas from watching spectacles? What if there were a handful of bigger trees and when you devoured them, they fell over? Or once your swarm is big enough, certain objects change to yellow to be devourable.
All that being said - don't feel obligated to put more work into your jam game. They're a blast to make and perfect for experimenting and learning. If you got what you need out of this game, then it's a huge success. :)