Comb hairs on the fourth tarsi are a well known character of theridiid spiders. They are supposed to insure that the spider does not get stuck in her own silk during sticky silk wrap attack. A few years ago I thought I was the first to find such hairs in the distantly related pholcids. However, it turned out that H. Lebert had seen these hairs 140 years ago (in 1874). He writes, on Pholcus phalangioides:
"...Auch finden sich am unteren Theile dieses Endgliedes eigenthümliche, nicht lange, starke, verhältnismässig breite Haare mit einigen seitlichen Haarauswüchsen, welche ungefähr die Hälfte der Breite der Basis dieser Haare zeigen, also ganz von Fiederhaaren verschieden sind; eine Art Haare, wie ich sie bei wenigen Spinnen angetroffen habe."
Our broad comparative study shows that pholcid comb hairs exist in two basic morphologies and are distributed in varying patterns on the fourth tarsi of males and females. It also provides new data for phylogeny reconstruction.
Photo: Comb hair in Belisana, (c) B.A. Huber