The velvet worm (also known as Onychophora) live in social groups of up to 15 individuals, which is headed by a dominant female. These groups live and hunt together. Because they are particularly vulnerable to dehydration they live in moist environments and spend much of their time hidden deep in soil. The group members will display aggressive behaviour towards members of other groups.
The Onychophora also uses its aggressive behaviour to establish and maintain a hierarchy within its own group. Higher ranking individuals will chase, bite and crawl over its subserviant group members. Young worms do not normally participate in aggressive behaviour but will crawl on to the backs of adults who will tolerate this. Onychophora measure each other up, running antennae over each other and form pairs which cluster together. This is called an aggregate and happens after hierarchy has been established. Hierarchy is usually established quickly within a group.
The velvet worm hunts its prey by night, feeding on any smaller invertibrates such as woodlice, small spiders and termites, although it can also capture anything its own size. Its slime is ejected to slow down its prey, allowing it to bite and inject its saliva into its food. The slime incapacitates the prey and the saliva breaks it down into liquid so that it can more easily be consumed. The saliva is reingested at the same time as the prey. The dominant female is always the first to eat in the group, followed by the rest of the females, then the males and finally the young.
The reproductive and life cycle of the Onychophora can be complex. Almost all species reproduce sexually, except for one in which no males have ever been found. All species do, however, bear some sexual dimorphism. The females are larger and have more legs than the males. Many of the females are fertilized just once during their life cycle. Sperm is transmitted between male and female in numerous creative ways and fertilization takes place internally. Gestation can take up to fifteen months and methods of transferring the sperm include depositing it on the side of the female so that it can be absorbed into the skin.
Sometimes fertilization takes place before the female reproductive system is fully developed, where the sperm is kept in a special reservoir. Here it can live for long periods of time. Between one and twenty-three offspring may be produced a year by any one female. The life of a velvet worm can be as long as six years, with full developmemt (from ovum to adult) taking up to seventeen months. The life cycle of a velvet worm does not include a larval stage and all young are born live.