A range of more familiar terms has emerged to describe relationships between symbionts and their hosts - derived from hitchhiking, hijacking, takeovers, partnerships - and the idea of a "trojan horse". Epidemiological terms are also used - such as "epidemic", "virus" and "plague".
Some other possibly-suitable terms are not being employed in this context so much - perhaps most notably, "stowaways" and "slipstreaming".
- Stowaway - a relatively harmless hitchhiker without the host's awareness or consent;
- Slipstreaming - gaining benefit from a host rather indirectly.
Both terms refer to types of commensalism.
There's some overlap between these concepts and the established idea of a free rider - however, I think there's some room for some nuanced variations of this basic idea.