Crane fly mating
Mating "frenzy" of crane flies. The picture was taken in my backyard (Riverside, CA) around 10PM (March 31, 2017). I see a lot of these crane flies this spring.
A female adult (lightly colored) is just emerging from her pupal skin. The adult emerges from the pupal skin that is only partially exposed from the ground. During this time, numerous mature males fly close to the ground searching the newly emerging female adults. As they find the newly emerging female adults, they (dark-colored, smaller individuals) land on her and wait until she completes her emergence. As soon as her abdomen is free from the pupal skin, the males compete for her. The first winner will get the honor of mating with her.