Let’s stipulate some translations. The Hebrew sheretz = “swarmer”; remesh = “creeper”; chayyah = “beast.”

In the original creation, swarmers are found only in the water (Gen 1:20-21), while creepers are on land (1:24-26). Only after the flood do swarmers swarm on earth (Gen 7:21 is the turning point). There are still creepers on land, but now they’re joined by swarmers.

Lev 11, which details clean and unclean foods, speaks repeatedly swarmers on land, and it introduces the unprecedented combination of swarmers (sheretz) that creep (ramash) on land (11:44).

Leviticus 11:10 also mentions water-swarmers, some of which are clean. From the perspective of Gen 1, swarmers on land are an anomaly. They don't belong there.

Not all swarmers are unclean, but perhaps their anomalous status helps explain the logic of impurity. They’re intruders from the sea, oceanic “Gentiles” in Israel’s land. To eat land swarmers is to incorporate idolatrous gentility.

There's a complication. Grasshoppers and locusts are edible, along with some other winged swarmers that leap from the earth (11:21-22). Equipped with wings and springy legs, they’re birdlike and make minimal contact with earth. They don’t inhabit the land, as other swarmers do, but live between earth and heaven.

Between Gen 1 and Lev 11, the category of swarmers has “evolved” or been elevated from sea creatures to cover earth to (partial) sky creatures.

Now: At least some swarmers “walk” on their belly (gachon; Lev 11:42), like the serpent (Gen 3:14). Maybe land swarmers are unclean because they’re serpentine.

That’s correct, except: In Gen 3, the serpent isn’t a swarmer or even a land-creeper, but a “beast of the field” (vv. 1, 14). He’s cursed to “walk” on his belly (3:14). The curse changes the serpent’s biological classification, from beast to land-swarmer. He's the very first creature in the latter category.

Thus: Belly-walking swarmers are unclean because they’re serpentine, anatomically similar to cursed serpents. And Yahweh doesn’t want Israel to have communion with serpents or to bring them into the inner parts of their bodies, whether individual or social.