Exploring the attachment of the Mediterranean medicinal leech (<i>Hirudo verbana</i>) to porous substrates.

Abstract

Haematophagous ectoparasites must ensure a reliable hold to their host during blood meals and, therefore, have evolved a broad spectrum of versatile and effective attachment mechanisms. The Mediterranean medicinal leech (<i>Hirudo verbana</i>), for example, uses suction on both smooth and textured air-tight substrates. However, preliminary studies showed that <i>H. verbana</i> is also capable of attaching itself to air-permeable substrates, where suction does not work. Using high-speed videography and mechanical tests, we comparatively investigated the attachment of <i>H. verbana</i> on both smooth and textured air-tight as well as on porous artificial substrates, also considering the influence of mucus on sucker surfaces. In general, the leech-specific locomotion cycle did not differ between the tested surfaces, and the leeches were able to reliably attach to both air-tight and porous substrates. From our results, we conclude that suction is presumably the primary attachment mechanism of <i>H. verbana</i>. However, secondary mechanisms such as mechanical interlocking with surface asperities and pores or capillary forces occurring at the interface between the mucus-covered suckers and the substratum are also employed. In any case, the rich repertoire of applicable attachment principles renders the organs of <i>H. verbana</i> functionally highly resilient.