The Stag Beetle. Le Cerf-volant. (sounds like le cerveau lent - slow mind!)
The French name [= flying stag] for this fairly common insect is also the French for a child's kite. A flying-stag seems a reasonable name for the beetle, especially so when you see several of them on a sultry late evening in June or July above the bushy trees hanging in the air like miniature helicopters with their horns held high. Perhaps it is the hanging heavy flight of the beetle that has its resonance in the heavy hanging flight of the kite and so the name is transferred. Only the male beetle flies like this. The female mostly sits on a branch and awaits the male. The great horns of the male are its jaws. They are useless for anything but ornament. They cannot even grasp a pencil let alone give you a nip. The female has more normal sized jaws and she can bite. Since the jaws of the male can only maintain a feeble grip, one wonders what is their function. One assumes that the males do not eat! Several years ago I collected several in flight and put them together in a box. Generally they ignored each other. Nevertheless one grasped another weakly around the 'waist'. Nothing further happened and it may have been just a chance encounter. The remarkable aspect was the very considerable variation in size of the males. The smallest was about half the size of the largest - up to 8 cms. long.
Since the 'horns' are an example of sexual dimorphism, one would normally assume that some sexual encounter favours the development of the 'horns'. Either it is male agression for territory or for a female or the female somehow selects the males with the largest 'horns'! Perhaps the 'horns' have a function in the mating process.
The feeding and growth all takes place in the larval stage. The larvae are fat white maggots up to 5 or 6 cms. long which chew their way through the soft dead wood of senescent trees which they do for up to three years. I have found numbers in the base of a fallen walnut tree. It is reported that the larvae can stridulate in their dark deep tunnels. That is, they make a noise and communicate. Perhaps if they get too close to each other, they hear this warning. The habitat of large trees with dead stems and hollows is vital for a number of increasingly rare, fascinating and beautiful beetles. Increasingly rare because people cut up and remove the apparently useless trees. It is good to know that authorities in France and Britain are beginning to protect woodlands with large senescent trees for this reason. In Britain the beetle used to be found chiefly in the south east in the London region where I first saw them. But I understand that they are spreading northwards.