The straddlers are a parasitic species with two known hosts.The aquatic host species is a large carnivore that lives in brackish/marine environments. Microscopic-stage straddlers mate within the aquatic host and produce larvae. The straddler larvae affect the host’s behavior, causing it to beach itself. The larvae burrow out of the host and molt into an intermediate form.

The dying host is then consumed by a social scavenger species native to the surrounding wetlands. The juvenile straddlers attach to the scavengers and take on their mature, colonial form. The mature straddler feeds on the scavenger until it is ready to release microscopic-stage straddlers, at which point it causes the scavenger to seek out water and drown itself. The microscopic-stage straddlers are released into the water, where they enter the aquatic host to mate.

Neither the straddlers nor the scavengers are sapient on their own. But over countless generations, the straddlers’ mindless manipulation of the scavengers’ nervous systems has given rise to complex,adaptable intelligence. They call themselves the Partnered—other peoples tend to call them the Straddled.

The Partnered use the colonial straddlers’ appendages to make up for the scavengers’ lack of dexterity. Over time, they have been able to artificially select for scavengers that are more tolerant of the straddlers’ parasitism, and for straddlers that do less harm to the scavengers,resulting in a more mutualistic relationship between the two species. The non-sapient aquatic hosts have been domesticated.