When Eugène Simon
returned from his expedition to Luzon in 1891, he brought with
him, among others, a highly unusual pholcid spider species from caves near
Manila. Unlike any other pholcid known at that time, males were
provided at their ocular region with a pair of horns that seemed to be
segmented. Simon was clearly struck by this feature, and devoted the
only two figures in the original description of this new species Pholcus bicornutus Simon, 1892 to
the male ocular region (see right). One year later, in his epochal
Histoire
Naturelle des Araignées, he used one of these figures again. In
both editions, the two-segmented horns are illustrated as being more or
less parallel in frontal view, with separate tips.More than 100 years later, when preparing the first revision of Pholcus (Huber 2011), I studied Simon’s type material of P. bicornutus. While one mystery of Simon’s ‘segmented horns’ could be solved, another one appeared. Scanning electron microscopy revealed that what had looked to Simon like ‘distal segments’ were in fact brushes of hairs that originated at the tips of the ‘basal segments’. Strikingly, however, the tips of these hair brushes were not separate as illustrated by Simon but appeared like ‘glued’ or ‘waxed’ together at their tips. Simon had clearly interpreted this as an artifact, and I tended in the same direction.
The present paper revises the Pholcus bicornutus group based on much larger samples than previously available and finally presents strong evidence that the ‘glued’ or ‘waxed’ hair brushes of P. bicornutus are not an artifact. What remains a mystery is the biological function of these hair brushes, and of the waxed hairs in particular.
Pholcus olangapo a close relative of Pholcus bicurnutus. 12. Male prosoma. 14. Female prosoma. 13, 15. Male ocular horns with modified and ‘glued’ or ‘waxed’ hairs, frontal and lateral views. Photos: B. A. Huber