Adhesive and frictional tarsal pads in stick insects

Insects rely on specialized attachment systems to adhere to and move across substrates. For this purpose, stick insects (Phasmatodea) employ two types of smooth attachment pads on their tarsi: the pretarsal arolium, responsible for adhesion, and the tarsal euplantulae, generating friction. These pads function complementarily during locomotion and are supported by secreted tarsal fluid inside the contact area. Although their general functional roles are understood, a comprehensive intra-species comparison of their structural, mechanical, and chemical characteristics has been missing. This thesis addresses these gaps by analysing and comparing the ultrastructure and mechanical properties of the arolium and euplantulae, as well as the chemical composition, morphological residues, and evaporation rate of their tarsal secretions in Medauroidea extradentata. Our findings show that both pads share a hierarchical, layered organization, yet differ substantially in their functional adaptations. The arolium exhibits thicker, more widely spaced cuticle rods, leading to a lower elastic modulus and higher adhesive forces. Its secretion contains a higher proportion of methylated cuticular hydrocarbons (CHCs), which are likely to increase fluidity and promote capillary forces. In contrast, the euplantulae feature denser, thinner cuticle fibers, resulting in greater stiffness and lower energy dissipation, their secretion contains less methylated CHCs, potentially enhancing its viscosity and promoting viscous forces. Despite these differences, both tarsal secretions exhibit similar morphological residues and evaporation rates. These results show that the structural and chemical properties of the attachment pads are evolutionarily fine-tuned to fulfill distinct roles. The study provides novel insight into structure-function relationships in insect adhesion systems and advances biomimetic applications in soft robotics and adhesive technologies.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Christian-Albrechts-Universität zu Kiel

Year

2026

Author dc:creator

• Thomas, Julian

Contributors dc:contributor

• Gorb, Stanislav
• Dirks, Jan-Henning

• Stick insects
• Tarsal secretion
• Arolium
• Euplantulae
• Functional morphology
• Mechanical properties
• Atomic force microscopy
• Scanning electron microscopy
• Biomechanics

Repository record source_url

https://macau.uni-kiel.de/receive/macau_mods_00007840

OAI identifier oai:identifier

oai:macau.uni-kiel.de:macau_mods_00007840