A few question about the meaning of ‘genesis of their labour’

A few question about the meaning of ‘genesis of their labour’

The passage below is from Fathoms: The World in the Whale Hardcover by Rebecca Giggs.

‘Something is everywhere and always amiss … It is as though each clay form had baked into it, fired into it, a blue streak of nonbeing.’ The blue streak of mortality: this was what Dillard was referring to. Yet whale worms, whale lice, whalesuckers are nonbeings too, set against the whale, the massive being that is their birthplace, habitat, and the genesis of their labour. For parasites are very like death: the faceless thing amiss, everywhere, finding purchase in even the most enfolded, sunless surfaces. Long considered indicative of sickness, derangement, and decline, the most unnerving quality of any parasite is its profuse, persistent vitality, the wiggling in the womb, the itch on the skin, clinging, consuming, breeding. Worse than a ghost somehow. A parasite will typically reproduce faster than its host, and may exist in greater plenitude; the million-faced beast upon the beast. Being more profoundly alive, according to these measures, than their hosts, parasites can, in contrast, make the larger animal itself seem ghostly and partial — for less of it consists of itself.

I have a few questions about the underlined phrase.

All through the passage the author shows distaste for parasites.

In the underlined passage I cannot understand the contextual meaning of

first, ‘labor’

(it’s common meaning is ‘work’, and also can be ‘trying to give birth’. I think in this context it’s work but I cannot exclude the latter since I don’t grasp the meaning of the whole phrase)

second, ‘genesis’

(it’s meanig in this context seems ‘origin’. Am I right?)

last, ‘genesis of their labour’

In this phrase ‘their’ stands for ‘parasites’, but even if I am right I don’t make out the meaning of the whole phrase.

Thanks in advance.