The Small Yellow Cluster Fly

In Cluster Flies, Pests, Pests in November, Pests in Winter

The Small Yellow Cluster Fly:
We were called to a regular fly problem in Bracknell. These files acted like Cluster Flies but looked very similar to fruit flies by their size and appearance. This year the number was at the highest we have ever seen, measuring in the hundreds of thousands. They were in stairwells of this block of flats and appear every year in the Autumn. As we were puzzled by these flies we sent them off to our lab who identifies insect specimens as well as rodent droppings. The results came back as: Thaumatomyia notata, the small yellow cluster fly. The size and colour of this Cluster Fly differ in the ‘normal’ Cluster Fly we normally deal with at PEST UK.

I have dealt with a situation involving this species in a new flat development in Reading. What happened here was that the buyer was concerned about flies in the windows and window frames. The agents selling the block got Rentokill in and I saw the technician who stated they were Fruit Flies. I disagreed, believing them to be Filter or Sewage Flies. We were both wrong they were the same species as the block of flats in Bracknell: (Thaumatomyia notata, the small yellow cluster fly). As the habits of this cluster fly as such that the potential purchaser of the flat would have a fly problem every year, the person bought a different flat in the bock on the other side (and unaffected) part of the building.

Where as the most common Cluster Fly (smaller than a Blue Bottle but larger than a House Fly) larvae is parasitic on earthworms during late Spring, Summer & early Autumn the Yellow Cluster Fly larvae feeds on aphids. The other type of Cluster Fly that is more common in rural areas is the Autumn fly. The larvae of this type of Cluster Fly feed on dung heaps and dung in fields. Treatment of Cluster Flies is generally a fogging insecticide treatment with a residual insecticide spray to windowsill, walls and ceilings.