Sticky or hairy?

[Mark Pajak]

http://news.bbc.co.uk/1/hi/england/cambridgeshire/8304164.stm

I thought that is was not secretions that stuck insects (and spiders) to things, but the micro forces created by dry setae on scopulate brushes on the tarsi?

Do insects do it differently and actually secrete fluid?

[Beatrice Smith]

Haha I have actually been reading about this today as part of my literature review!

Anyway, there are a number of different mechanisms which spiders, insects and some lizards use to cling to smooth surfaces. These can be divided into two basic types, wet and dry. Wet is obviously when fluid is secreted, and is found in some insects such as flies. Dry is more interesting, at least to engineers! Dry sticking can be with hairs, or suckers. Grasshoppers use suckers, and these work as you would expect. Spiders and geckos have loads of tiny hairs on the bottoms of their feet, which then divide into even smaller hairs. These help the animal cling to the wall using a combination of friction (as the large number of hairs gives a very high surface area), capillary action (as water condenses between the hairs and the surface and helps the animal stick) and the van der waals force, which is an electrostatic force which holds molecules together, and only works over very small distances. There has been a lot of research and debate as to which of these forces is the most important, and lots of people are making tape and post it notes inspired by insect and gecko feet. Anyway, this coating seems to be designed to stop insects like flies (which are probably one of the most undesirable due to carrying disease etc), but it might not have an effect on other creatures which use dry adhesion.

As an aside, does anyone know if it is just A. Seemani that produces webbing from its feet to help it climb, or do all tarantulas?