The females metamorphose into a parasitic stage when they attach to a host and enter into its skin.

Due to their large size and mesoparasitic life history there have been a number of studies of Pennella, the members of which are among the largest of the parasitic Copepoda.

The female has a two host life cycle and egg production commences when an inseminated female settles on its ultimate host, usually a large marine fish such as a member of the cod family Gadidae or tuna.

Before the parasite settles on the intermediate host there are two free swimming or copepodid larval stages, after which it settles on the gill tips of the intermediate host as a sessile chalimus larva.

After four chalimus stages on the intermediate host the parasite becomes sexually mature and the free swimming males begin to copulate with the females while they are still sessile, a week after attaining maturity the females leave the intermediate host.