Phoresy: a hitch-hiker’s guide.
Delve into phoresy (say four e see) and you quickly find yourself in the realm of the unknown. Phoresy is where an animal uses a larger animal as transport to get to another place. Literally a hitch-hiker. I remember as a youngster finding bumblebees with tiny buff-coloured mites – related to spiders – clinging on tightly to their body hairs. Sometimes there would appear to be dozens of them. For a long time their presence remained a mystery to me until I learned that all they were doing was using the bee to get from one place to another.
Another unsuspecting taxi turns out to be the shiny black lumbering dor beetles that are sometimes seen wandering sedately along paths in summertime, in search of a fresh cowpat or rabbit dropping on which to mate and lay their eggs. In this case the mites can be found clinging to hairs on their undersides. It turns out that there are literally hundreds of creatures that unknowingly give lifts to a wide variety of invertebrates. It is not unknown for snails to be transported by birds like plovers. Some regular hitch-hikers even have legs modified with sucker pads to help them cling on.
A much more sinister group on the lookout for passage to pastures new can be the army of parasites that live on the skin, feathers and fur of animals, including the loathsome (to us) bloodsuckers. Whenever their host dies they need to find another one pretty quickly or they in turn are doomed. They die from cold as their host’s body cools down. They wait on the surface of the corpse andtry to latch on to any passing body whose surface feels rough or warm. Many of them will take a meal even on an unsuitable body, just to tide them over, in the hope that they will eventually find the right host species to live on.
September is the month when countless billions of other little aviators take to the skies in search of a place to set up home. These are spiders, young and adults, of hundreds of different species. Many times I have watched these minute beasts, many of them no larger than a pin’s head, as they clamber to the tip of a blade of grass. There they pause, and point their hind ends towards the sky. They begin to pay out a tiny gossamer thread of finest silk, which is caught by the slightest breeze. Then, when the thread is long enough to support their weight they release their grip and off they go. Spiderlings have been trawled from the air having been carried well into the upper atmosphere. Potentially they could circumnavigate the globe, but as always there is a down side. Because these little pilots are at the mercy of the wind they cannot decide where they come to land. Billions of them must perish on water bodies, and especially the great oceans. Billions more will be snapped up by birds like swallows, martins, and swifts.
Spiders are capable of laying hundreds of eggs. If any more than two of each brood survive to mate and reproduce, we would quickly be up to our eyes in them. Such is the measure of failure that this never happens. Nature is a hard taskmaster!
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