It's a bit early in the year for the fungal part of my brain to kick into action, but occasional summer specimens can stimulate the old grey matter.
This is Panaeolus ater, which is 'hygrophanous': it changes colour according to whether it is wet or dry. The dry weather has put it into this (very) dry state:
Panaeolus species are relatively easy to identify to family due to the mottled gills:
The larvae of many fly species eat the mushroom fruit-bodies, often consuming them to destruction, and you can be sure that if there are fly larvae around, then an ichneumonid won't be far behind them. This minute one was prospecting the outside of the caps, so I suppose it can detect them from there without having to go down and search each gill individually.
The timing of this parasitisation is critical: the mushroom fruitbody will only be there for a few days during which the fly larva must progress from egg to pupation. So the ichneumonid must locate the fly larva (and the mushroom!) during that very short time. That's at least a quadruple dependency: the ichneumonid depends on the fly larva which depends on the mushroom which depends on its host (usually a plant, dung or wood). And, of course, the host will have its own set of criteria for being there....
The timing of this parasitisation is critical: the mushroom fruitbody will only be there for a few days during which the fly larva must progress from egg to pupation. So the ichneumonid must locate the fly larva (and the mushroom!) during that very short time. That's at least a quadruple dependency: the ichneumonid depends on the fly larva which depends on the mushroom which depends on its host (usually a plant, dung or wood). And, of course, the host will have its own set of criteria for being there....Staying with ichneumonids, this one is very numerous at the moment as it runs over and under leaves looking for caterpillars:
