Other development includes designs that find inspiration in nature, especially in animals that are able to climb walls and ceilings such as geckos,       various species of insects  , tree frogs  , or chameleons. Mechanisms of insects that can scale walls and ceilings help understand how to produce surfaces with extremely high friction that don't exhibit too much sticking for practical applications. Abilities of geckos have been intensively studied to find out how sticking of vertical walls or ceilings can be joined with ability of easy and quick detachment that enables geckos quick movement. It has been discovered that Van der Waals force rather than friction or adhesion is the most important mechanism behind gecko's abilities. This implies that artificial designs mimicking geckos' feet should rely on maximizing surface contact between object and the pad, which is less practical in some situations, for example when pads are used on non-flat surfaces or when objects put on the pad don't have flat surfaces. On the other hand, mechanisms in geckos' feet help design materials with reliable sticking and easy detachment at the same time. Mechanisms used in geckos, tree frogs and some insects were also studied for self-cleaning ability, which would enable artificial materials retain the ability to prevent sliding after continuous use in dirty environments.