Adam Clarke on Leviticus 11:20

All fowls that creep - Such as the bat, already mentioned, which has claws attached to its leathern wings, and which serve in place of feet to crawl by, the feet and legs not being distinct; but this may also include all the different kinds of insects, with the exceptions in the following verse.

Going upon all four - May signify no more than walking regularly or progressively, foot after foot as quadrupeds do; for it cannot be applied to insects literally, as they have in general six feet, many of them more, some reputed to have a hundred, hence called centipedes; and some a thousand, hence called millipedes; words which often signify no more than that such insects have a great number of feet.