Prehistoric Mite Caught Hitching A Ride On A Spider

Scientists have produced amazing three-dimensional images of a prehistoric mite as it hitched a ride on the back of a 50 million-year-old spider.

At just 176 micrometers long and barely visible to the naked eye, University of Manchester researchers and colleagues in Berlin believe the mite, trapped inside Baltic amber (fossil tree resin), is the smallest arthropod fossil ever to be scanned using X-ray computed tomography (CT) scanning techniques.

They say their study – published in the Royal Society journal Biology Letters on Wednesday, 9 November – also sets a minimum age of almost 50 million years for the evolution among these mites of phoretic, or hitchhiking, behavior using another animal species.

“CT allowed us to digitally dissect the mite off the spider in order to reveal the important features on the underside of the mite required for identification,” said Dr David Penney, one of the study’s authors based in the Faculty of Life Sciences. “The specimen, which is extremely rare in the fossil record, is potentially the oldest record of the living family Histiostomatidae.

“Amber is a remarkable repository of ecological associations within the fossil record. In many cases organisms died instantaneously and were preserved with lifelike fidelity, still enacting their behavior immediately prior to their unexpected demise. We often refer to this as ‘frozen behavior’ or palaeoethology and such examples can tell us a great deal about interactions in ecosystems of the past. However, most amber fossils consist of individual insects or several insects together but without unequivocal demonstrable evidence of direct interaction. The remarkable specimen we describe in this paper is the kind of find that occurs only once in say a hundred thousand specimens.”

Fellow Manchester biologist Dr Richard Preziosi said: “Phoresy is where one organism uses another animal of a different species for transportation to a new environment. Such behavior is common in several different groups today. The study of fossils such as the one we described can provide important clues as to how far back in geological time such behaviors evolved. The fact that we now have technology that was unavailable just a few years ago means we can now use a multidisciplinary approach to extract the most information possible from such tiny and awkwardly positioned fossils, which previously would have yielded little or no substantial scientific data.”

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