Winter in the Midwest includes below freezing temperature and slipping on ice. Why is ice slippery? Loss of friction! When we put pressure on ice with our foot, the thin layer on top melts due to the increase in pressure. The thin layer of water can move freely and lowers the friction between our feet and the ground. The water has a much lower coefficient of friction than does dry land, thus our feet fail to get sufficient traction on ice. We are gliding on a thin film of water.
Friction increases with weight. Large animals, such as humans, can generate plenty of friction on dry ground. Very large animals, such as elephants, have enough weight to generate a lot of friction on a relatively flat foot. Feet (elephants have much larger feet than humans) are a small enough size to create sufficient friction for walking, yet large enough to keep the animal from sinking too far into the ground.
Like a person walking on ice, an insect with flat feet would have trouble getting traction on dry land because of their small size and weight. To gain traction, insects make use of an array of claws and spines or in some cases sticky hairs.
The end segment of an insect leg, the tarsus, often contains a claw. The claw can dig into the ground or into the stems or leaves of plant, much the way that cleats on shoes will provide additional traction for human athletes. The ability to dig into the ground is a function of the pressure applied. The pressure generated is the weight divided by the surface area. Insects have little weight to generate friction or pressure. Instead, insects maximize the pressure (weight per unit area) by reducing the area. By putting all of its weight on the small surface area at the end of a claw, insects can gain the traction they need without slipping and sliding through life.