This is one of the Dark-winged Fungus Gnats. It is the family Sciaridae and it is closely related to the Mycetophilidae. This group has eyes that meet behind the antennae (which you can see if you look closely here). This is a smaller family in the US. But many of these are apparently very common. This particular species is remarkably common in the spring. And can collect in impressive numbers on screens and porches near suitable habitat. They can be pests in mushroom growing cellars and the larvae do develop in fungi species. Some of the species favor the roots of plants.