A secondary function of the glands is defense. When severely frightened most mustelids will discharge musk, probably as a reflex action. Perhaps from such beginnings, the musk glands of the New World skunks and some of the Old World polecats evolved into effective defense weapons, supported by unmistakable warning displays in their behavior and striking color patterns in their coats. The reproductive habits of mustelids are remarkable for several unusual features. During the temporary truce in the mating season the male seizes the female by the scruff of the neck and may drag her about vigorously before mounting.
Copulation is repeated and very prolonged, up to one to two hours, even in the weasels.
The penis is stiffened by a bone, the baculum, which facilitates the long copulation. The whole procedure seems calculated to thoroughly arouse the female and is associated with induced ovulation. Prolonged mating may expose the pair to dangers from larger predators, but this risk is outweighed by the advantage of virtually certain fertilization. After mating, the fertilized egg travels to the uterus, as is usual in mammals, developing as it goes, into a ball of cells called a blastocyst. In most mammals, the blastocyst implants into the uterus wall within a few days and development of the embryo proceeds.