I was thinking it would be some royal jelly situation, I think that might just relate to bee's but with the honey being a resource it seemed fitting. Since it is a fun sandbox, it could be made so that when a side gets the jelly. It also raises the amount of eggs they need to win, making bigger egg-laden queens a side benefit. You could make it so that once one side gets it, another would spawn much closer to the opposing queen's side. My idea was that it might add some risk-reward to have to tie resources up at a spot separate from the honey for the possible benefit of being stronger in the long run. If only temporarily. You could also make it so that you can force-feed it to the enemy queen, so that she has to spend more time gathering eggs if she gets closer to victory than you. At the cost of her side being more powerful.
Viewing post in sandbox mode + feedback on victory reward comments
now that I think about it, a royal jelly upgrade to max capacity would actually be totally fine if the jelly were located off to the side in a spot where no honey could spawn, so you'd have to choose between the jelly and the honey. maybe even as an exclusive drop from a bee queen at that location, so it would require combat as well as gathering. I don't mind that at all actually