Plague of March flies

Plague of March flies

Observation - Plague of March flies - Southern Africa. Description: Thousands of March flies have been emerging in our vegetable garden over the past few weeks. Yesterday the walls were full of them. I noticed a week ago that the adults were emerging from the soil, and on closer inspection observed hundreds of small black

Thousands of March flies have been emerging in our vegetable garden over the past few weeks. Yesterday the walls were full of them. I noticed a week ago that the adults were emerging from the soil, and on closer inspection observed hundreds of small black pupal cases on the soil of the vegetable garden. We have noticed these flies before but never in such numbers. It's September, so I assume that they are from the northern hemisphere. Does anyone know what they eat?