Perhaps because the wing lice are in such a tenuous situation they are more likely to be hopping a ride. They already have the anatomical tools. Askew (Parasitic Insects, 1971) offers a number of other reasons that might influence host shifts in lice. He ends the discussion on lice with a discussion of phoresy (hitchhiking). At that point in time, Askew was under the impression that phoresy was rare, primarily because carriers are "only rarely specific parasites of the same host as the lice, and it (phoresy) offers only a slim chance of survival to the lice". Perhaps because these wing lice are on an edge already, hopping off may represent as good a choice as staying on (see suicidal aphids) whereas those that are hunkered down don't like those odds. The case that he uses as an exceptional illustration to this rule relates to starling lice which attach to the hippoboscid, Ornithomya fringillina. He points out that while O. fringillina is not host specific to starlings, since starlings are so common, this lice is likely to be given a directed ride and therefore a good chance at the right host. I suspect that lice on less common birds and with a less host specific taxi service might be less likely to take a ride. Of course, each situation has its own balancing act between dispersal and survivorship. Harbison and Clayton's study is wonderful in examining this interaction and its implications so directly.