It doesn’t explain why they pick a target in the first place; but I suspect that, once they do, they (either deliberately, or in death) hose the thing down with signal pheremones nice and thoroughly, ensuring that their swarm mates will be all over it until the traces finally dissipate, which can take a while.
Though, if they are doing that, pheremone baits would be another option. We did a little experiment in BIO, some years back, with a species of termite whose trail-forming pheremone apparently has close chemical similarity to an ingredient in the ink of cheap bic ballpoints: Just draw some lines, and the termite would obediently go all line-following-robot on them, regardless of how purposeless the pattern. Probably what it feels like to be in advertising, on a smaller scale.
