Having Fun Guys On That Vanishing Mushroom?

Another case where I would have been better off using my macro lens but unusually I didn't take it on our morning walk. This fungus had sprouted on a pile of ash chippings and it wasn't until I trained the 400mm on it that I saw the pair of mating gnats.

I think the fungus is a Coprinoid/ink cap, specifically a Coprinous aqueous or spitting ink cap. When I returned a couple of hours later it had shrunk to almost nothing.