Some of the more out there UFO theories postulate on these lines. An idea that rather than say send an explorer of your own species to some planet with all the needed life support, you use genetic engineering to create a worker bee essentially, already tailored to perform whatever function under whatever environmental conditions are present at the target planet. You may even be able to build this species using genes already present at the host system in some reduced to essential components fashion like an engineered plasmid in the molecular biology lab. This would also double as camouflage keeping the worker bee genetics separate from genetics found in your own planet or star system, making them appear endogenous to the target planet instead.