Jamieson, Fausset and Brown on 2 Peter 2:12

12. (Jude 19).

But--In contrast to the "angels," 2Pe 2:11.

brute--Greek, "irrational." In contrast to angels that "excel in strength."

beasts--Greek, "animals" (compare Psa 49:20).

natural--transposed in the oldest manuscripts, "born natural," that is, born naturally so: being in their very nature (that is, naturally) as such (irrational animals), born to be taken and destroyed (Greek, "unto capture and destruction," or corruption, see on Ga 6:8; compare end of this verse, "shall perish," literally, "shall be corrupted," in their own corruption. Jude 10, naturally ... corrupt themselves," and so destroy themselves; for one and the same Greek word expresses corruption, the seed, and destruction, the developed fruit).

speak evil of--Greek, "in the case of things which they understand not." Compare the same presumption, the parent of subsequent Gnostic error, producing an opposite, though kindred, error, the worshipping of good angels": Col 2:18, "intruding into those things which he hath not seen."