Walking Stick Hanging

In previous posts, I have mentioned that the most distal (fifth tarsal segment) segment of the walking stick leg differs from the four proximal segments. A tarsal claw arises from the fifth segment and the “pad” of the fifth segment (called the arolium) differs in structure from the pads on the previous four (euplantulae). The euplantulae are friction pads that grip when the leg is pushed down. The arolium is an adhesive pad that generates stronger grip when the leg is pulled away from the surface. This happens naturally when climbing vertically or upside down on horizontal surfaces.

A walking stick hanging upside down will only engage its arolium (see image below). The euplantulae are not engaged. If the leg slips and is pulled back toward the body, the adhesive arolium will grip the surface and prevent the stick insect from slipping or falling.

The different parts of the tarsi have complementary functions. The claw grips the surface and gives the leg traction as it pulls its body forward. The euplantulae grip the surface as the leg pushes back and the body moves forward. This allows the insect to walk rapidly in an upright posture. The arolium is used to cling to surfaces, walk and climb where the claws and the euplantulae provide minimal grip.

Hanging Stick Insect

Upper: A Stick Insect Hanging Upside Down Grips the Surface With Its Arolium (distal tarsal pad)
A, B The ariolium (distal pad)
C-F Euplantulae (proximal pads)
Image From: Labonte & Federle*

*Labonte, David, and Walter Federle. “Functionally Different Pads on the Same Foot Allow Control of Attachment: Stick Insects Have Load-Sensitive “Heel” Pads for Friction and Shear-Sensitive “Toe” Pads for Adhesion.” PloS One 8.12 (2013): e81943.

About jjneal

Jonathan Neal is a retired Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
This entry was posted in behavior, by jjneal, Taxonomy. Bookmark the permalink.

1 Response to Walking Stick Hanging

  1. Arthur says:

    Hello, I would like to know if there is a cheap and easily found material that counters ariolium’s function, I mean one material that doesn’t allows the ants (for example) to climb.

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