ORIGINAL PAPER Senta Niederegger ® Stanislav Gorb ® Yuekan Jiao Contact behaviour of tenent setae in attachment pads of the blowfly Calliphora vicina (Diptera, Calliphoridae) Accepted: 31 October 2001 / Published online: 7 December 2001 Ó Springer-Verlag 2001 Abstract To enable strong attachment forces between padandsubstrata,ahighproximitybetweencontacting surfaces is required. One of the mechanisms, which can provideanintimatecontactofsolids,isahighflexibility of both materials. It has been previously presumed that setae of hairy attachment pads of insects are composed of flexible cuticle, and are able to replicate the surface profile.Theaimofthisworkwastovisualisethecontact behaviourofthesetaebyfreezing-substitutiontechnique to understand setal mechanics while adhering to a smooth surface. This approach revealed considerable differences in the area of the setal tips between con- tacting and non-contacting pulvilli. Based on the assumptionthatsetaebehavelikeaspringpushedbythe tip,aspringconstantof1.31Nm –1 wascalculatedfrom direct measurements of single setae by atomic force microscopy.Inordertoexplaintherelationshipbetween the behaviour of the attachment setae at a microscale and leg movements, high-speed video recordings were made of walking flies. This data show that some proxi- mal movement of the leg is present during contact formation with the substrate. Keywords Cuticle ® Adhesion ® Pulvilli ® Scanning electron microscopy ® Atomic force microscopy Introduction The hairy attachment system of flies has been studied for more than 300 years. Numerous studies have been conducted to understand the anatomy and function of the system, as well as the design of the fly pretarsus. Nevertheless, there remains a lack of agreement on solutionsconcerningtheattachmentmechanismofthefly walking on smooth surfaces. Different hypotheses have beenproposedtoexplainthemechanismofattachment. Theories of a sticky fluid (Dewitz 1884), microsuckers (Simmermacher 1884), and the action of electrostatic forces have been discussed (Gillett and Wigglesworth 1932). Based on experiments with beetles, these theories havebeenrejectedandithasbeenconcludedthatcohesive forces,surfacetensionandmolecularadhesionofthepad secretionareinvolvedinthemechanismofattachmentof thehairysystem(Stork1983b). To enable strong attachment between pad material and diverse substrata, a high proximity between con- tacting surfaces is required. One of the mechanisms, which can provide an intimate contact of solids, is high flexibility of at least one of both materials. It has been previously presumed that setae are composed of flexible cuticle, and are able to replicate the surface profile (Bauchhenss1979;Stork1983b).Ifthesinglesetaeofthe adhesive pads are adapted to deform under load and fit themicrotextureofsurfaces,contactwiththemaximum number of attachment points would be possible, inde- pendent of the substrate profile (Blackwell 1930; Bauchhenss and Renner 1977; Bauchhenss 1979; Stork 1980, 1983b; Ro¨der 1984; Wigglesworth 1987). This hypothesis, however, has not been properly tested. Theaimofthisworkwastovisualisethecontactbe- haviourofthesetae,tounderstandsetalmechanicswhile adhering to a smooth surface. The general anatomy of the fly pretarsus and quantitative data on the arrange- mentofthetenentsetae,studiedinthescanningelectron microscope(SEM),wereanimportantsetofdataforthe detection of differences between pulvilli contacting a substrateandpulvillinotincontact.Thebasicideawas torevealdifferencesintheareaofthesetaltipsbetween contactingandnon-contactingpulvilliinordertogetan impression of the degree of material flexibility. Data obtained from direct measurements of the spring con- J Comp Physiol A (2002) 187: 961–970 DOI 10.1007/s00359-001-0265-7 S. Niederegger (&) ® S. Gorb ® Y. Jiao Biological Microtribology Group, Biochemistry Department, MPI of Developmental Biology, Spemannstr. 35, 72076 Tu¨bingen, Germany E-mail: senta.niederegger@tuebingen.mpg.de Tel.: +49-7071-601360 Fax: +49-7071-601447