Where does the larval stage of a cluster fly develop?

The cluster fly's larval stage develops specifically in earthworms. After female cluster flies lay their eggs, the larvae seek out a suitable host, which happens to be earthworms. Upon hatching, the larvae enter the earthworm's body and feed internally. This association with earthworms is a critical aspect of the cluster fly’s life cycle and is important to understand in the context of their developmental biology and ecology.

The other options do not represent the correct habitat for the larvae. Cluster flies do not utilize tree bark, animal carcasses, or decaying leaves for larval development, illustrating the unique relationship between these flies and earthworms in their environmental niche. Understanding this specific larval development stage is essential for controlling cluster fly populations effectively and appreciating their ecological roles.