After a caterpillar eats a leaf, it can convert the chemical energy into energy to it build a cocoon.

heat
nuclear
chemical
mechanical

mechanical

Explanation:

The process of most of the organisms in the world is to eat something in order to convert the chemical energy that food is providing into ATP molecules that he than can convert into mechanical energy to carry out different process, the caterpillat eats the leaf and with the ATP that digestion creates the caterpillar then can create mechanical energy to build a cocoon.