In its northern and western range the sp. is known only from a few islands. It occurs in S England and E Wales, the Isle of Wight and the Polish island Wolin. Records prior to 1913 are available from Sjtelland and Vendsyssel. From 5 further islands only single and doubtful records are known which, apart from Bornholm, are all more than a century old; viz. Corsica, Sardinia, Sicily, and Crete. The sp. has not been recorded from any other island in the Baltic, the North Sea, the English Channel, the Atlantic Ocean, or in the western Mediterranean. In SE Europe it inhabits numerous islands in the Ionian and Aegean Seas. – Four different hypotheses for the absence of P. pennipes on the islands in its northern and western range are discussed.