If an animal mates with another species of animal, is it still bestiality?: Onychophorans and outbreeding depression.

I promised more obscure invertebrates, so here is an onychophoran. Onychophorans are forest leaf litter dwellers. I have never seen one, but I live in hope. Their common-or-garden name, velvet worms, seems to suggest that holding one would feel like being stroked with a piece of velvet. As a presumptive scientist, I have qualms about using a word like 'cute', but look at those little antennae. I'm only human!

Onychophorans are also wonderful because they are freaks. I have a soft spot for animals who exist in distant, unclassifiable, evolutionary backwaters. Onychophorans appear to be related to both insects and annelid worms, but cannot be classified as either. They exist in a phylum all of their own. To put this in perspective, human beings are in the phylum Chordata, along with (more or less) everything else that has a backbone. The phylum Onychophora contains only onychophorans. 

Germaine Greer reputedly remarked the other day that she was an animal. Perhaps Germaine should consider becoming an invertebrate. In the tradition of female-dominated ant, bee and termite societies, and female praying mantises who devour their mates after sex, some onychophorans live under a rigid matriarchal hierarchy. 

The Australian species Euperipatoides rowelli commonly lives in a social group of up to 15 females, males and young. They hunt as a pack, immobilising their prey with a sticky secretion of mucus. The group observes a strict hierarchy in the order in which they feed. The dominant female feeds first, followed by other females, then the males and young. According to biologists who made this discovery, 'hierarchy within the group is established by aggressive-dominant and passive-subordinate behaviours'. At least there are no passive-aggressive onychophorans. 

Aggressive behaviour consists of kicking, biting, chasing and climbing on other individuals. Passive behaviour involves running away or allowing oneself to be climbed on. Females are commonly larger than males, and this may explain their higher status. Onychophorans of this species have been observed running their antennae over others' backs, perhaps to estimate their size and social status. 

However, while it's a dog-eat-dog world inside the onychophoran pack, they close ranks against outsiders. To quote the aforementioned biologists, 'E. rowelli from different groups, ie. from different logs, are met with intense agression'. Perhaps Germaine is right. It seems all too easy to draw parallels with the human condition. Personally, when I see someone from a different log, I can barely contain myself. But first I run my antennae over their back, just in case. 

Unfortunately for onychophorans, fragmentation of their habitat means it's sometimes difficult to find a mate, so they resort not to inbreeding, but to outbreeding. To explain by way of analogy, onychophorans are not like the hillbilly who marries his cousin, but the hillbilly who marries his goat. Unable to find a mate of the same species, they will breed with a different species of onychophoran. As with many cross-species matings, the resulting offspring often have fertility problems, as well as unusual numbers of legs.