What is a key identification feature of cluster flies?

Cluster flies are often identified by their distinctive yellow hairs on the thorax, which provide a unique feature when trying to differentiate them from other types of flies. This characteristic helps entomologists and pest control professionals recognize cluster flies in the field effectively.

The presence of these yellow hairs is particularly notable since it sets them apart visually from other fly species that might not have such distinctive coloration on the thorax. This identification feature is crucial for proper pest management, as it allows for accurate species identification that informs appropriate control measures.

In contrast, the other characteristics listed—such as being brightly colored, having no wings, or being very small—do not apply to cluster flies. They may not exhibit bright colors like some other insects, they do possess wings and are of a size typical of fly species, making these traits less relevant for identification purposes.