simple first year physics says that small guys are predisposed to being able to lift more weight in proportion to their body weight...
Scaling of Area and Volume:
A small insect such as an ant can carry many times its own weight when foraging for food for its colony. On the other hand, large animals, such as elephants, would have difficulty in carrying anything near their own weight, Would an elephant-sized ant be stronger than an elephant?
The answer is no. The ant's thin legs would not be strong enough to hold even its own weight up, let alone anything else. Notice how thick the elephant's legs are in relation to its body.
The concept which is relevant here is called scaling. The strength of a support, such as the elephant's leg, depends on the cross-sectional area, so we say that strength scales with area. On the other hand, the mass of an object like the elephant depends on its volume, so weight scales with volume.
If we increase the volume without increasing the surface area, we are increasing the amount of force per unit area and eventually the support will fail. We define the term pressure to be this force per unit area:
Pressure = Force/Area
research 'scaling of area and volume' if you want a more detailed explanation...