by Ricardo L. Palma, Curator of Terrestrial Invertebrates
Evolving without wings, humans dreamed about flying for thousands of years… but only just over 100 years ago they invented a heavier-than-air machine which could fly and take them to the skies.
However, long long ago, natural evolution had already provided the opportunity to fly to creatures without wings. Yes, these wingless animals acquired the ability to “fly” by using Nature’s “aeroplanes”!
Typical groups of animals that live their entire lives flying by “hitchhiking” are most parasites of birds and bats. All lice and feather mites, many fleas and some wingless flies move about holding safely onto their flying hosts. However, some bird lice have become “double” hitchhikers by acquiring the capacity of taking rides on flying insects, which are not their regular hosts but which “land” on the bird’s plumage with other purposes, like engorging themselves with the warm blood of the host.
This phenomenon, known as “phoresy” or “phoresis”, allows lice to move from one host to another even when there is no close contact between them. For a louse, it is certainly a most convenient way to disperse and invade new hosts, without having to wait until its host touches another. The most frequent flies used by lice to hitchhike are called “louse-flies” because they are flat (like lice), and they are attracted to birds to feed on their blood.
However, parasites are not the only creatures able to hitchhike on flying insects… soil mites, false-scorpions and other small invertebrates which normally live in the leaf litter have also “learnt’ to move around by holding on to the legs or body of common flies, mosquitoes and crane-flies.
Finding and collecting or photographing flying insects with hitchhiking passengers is infrequent and not easy. I have been collecting and observing lice living on birds for over 45 years and I have not yet been able to record a phoresy case. However, a group of researchers working on Tiritiri Matangi Island in the Hauraki Gulf, near Auckland, have collected a louse-fly which has three lice attached to its body. Comparing them against other louse samples kept in the Te Papa collection, I have identified the hitchhiking lice as originating from a saddleback, a unique endemic New Zealand bird, which now only lives on islands free of mammalian predators.