Stag beetle  (Lucanus cervus)

Larvae: stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
Mandibles: the pair of mouthparts most commonly used for seizing and cutting food, common to the centipedes, millipedes and insects.
Pupating: the process of forming a pupa, the stage in an insect's development, when huge changes occur that reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis.
Thorax: part of the body located near the head in animals. In insects, the three segments between the head and the abdomen, each of which has a pair of legs.