[zaarn]

Bacteriophages attach to certain receptors, they don't respond to any stimuli.

The entire process of injecting their RNA is simply a chemical reaction to being attached to a receptor.

Basically, they just drift along until they hit a bacteria with the right receptor, then inject their genetic material and the empty hull is either discarded or simply continues to hang onto the cell.

The outer hull of the phage doesn't do a lot.