Why does the tom grab the female by the scruff of the neck when mating?

At first sight this appears to be a piece of macho brutality, in similar vein to the cartoon caveman grabbing his mate by her hair and dragging her off to his cave. Nothing could be further from the truth.

In sexual matters it is the female, not the male, who is dominant, where cats are concerned. Toms may fight savagely among themselves, but when they are sexually aroused and attempting to mate with the queen they are far from bossy. It is the female who swipes out and beats the toms. The bite on the back of her neck may look savage, but in reality it is a desperate ploy on the part of the male to protect himself from further assault.

This protection is of a special kind. It is not a matter of forcibly holding down the female so that she cannot twist round and attack him.

She is too strong for that. Instead it is a 'behaviour trick' played by the male. All cats, whether male or female, retain a peculiar response to being grabbed firmly by the scruff of the neck, dating back to their kitten days. Kittens have an automatic reaction to being held in this way by their mother. She uses it when it is necessary to transport the kittens from an unsafe to a safe place. It is crucially important that the kittens do not struggle on such occasions, where their very lives may be at stake. So felines have evolved a 'freeze' reaction to being taken by the scruff of the neck – a response which demands that they stay quite still and do not struggle. This helps the mother in her difficult task of moving the litter to safety. When they grow up, cats never quite lose this response, as you can prove to yourself by holding an adult pet cat firmly by the skin of its neck.

It immediately stops moving and will remain immobile in your grasp for some time before becoming restless. If you grasp it firmly on some other part of its body the restlessness is much quicker to occur, if not instantaneous. This 'immobilization reaction' is the trick the toms apply to their potentially savage females. The females are so claw-happy that the toms badly need such a device. As long as they hang on with their teeth, they have a good chance that the females will be helplessly transformed into 'kittens lying still in their mother's jaws'. Without such a behaviour trick the tom would return home with even more scars than usual.