Where does the larval stage of the cluster fly develop?

The larval stage of the cluster fly develops inside earthworms. This is a fascinating aspect of their life cycle, as cluster flies, particularly the species Pollenia rudis, are known to be parasitic in their larval stage. The adult female cluster fly lays her eggs near or in the soil, where the larvae will then seek out an earthworm to invade. Once inside, the larvae will continue to develop, feeding on the tissues of the earthworm until they mature into the adult stage. After they complete their development, they exit the earthworm, typically resulting in the host's demise.

This unique reproductive strategy highlights the parasitic relationship cluster flies have with earthworms, differentiating them from many other insects whose larvae develop in more accessible environments, such as water or decaying plant material.