Mary Douglas writes in Leviticus As Literature that the word translated as “swarming” or “creeping” should instead be translated as “teeming,” with its connotations of fertility.  Israel is to avoid teeming things, Douglas argues, because Israel is to make a distinction between covenant and fertility.  Israel is not to hate but to shun teeming things; they are to leave them be.

This is initially counter-intuitive: The covenant promises fertility, and central to the covenant promise is the promise of abundant seed.  But Douglas may be onto something, because fertility for Abraham and his children does not come through flesh but through the Spirit (cf. Galatians 4).  The circumcised people has renounced teeming in cutting off the flesh, and instead looks to Yahweh as the Lord and Giver of life.