ABSTRACT
Aggressive behavior is so widespread in the animal kingdom that it is virtually universal in some form or another in almost every animal which has the necessary motor apparatus to fight or inflict injury. It is absent or rare in only those invertebrates such as some worms and oysters which have no means of inflicting damage, whereas it is common in most arthropods and vertebrates which have appendages, claws, teeth, or other structures capable of damaging movements. Lobsters, crayfish, spiders, most insects, and most vertebrates are all capable of severe aggressive behavior, which can be seen in both natural and experimental conditions.
