Adam Clarke on Psalms 78:49

By sending evil angels - This is the first mention we have of evil angels. There is no mention of them in the account we have of the plagues of Egypt in the Book of Exodus, and what they were we cannot tell: but by what the psalmist says here of their operations, they were the sorest plague that God had sent; they were marks or the fierceness of his anger, wrath, indignation, and trouble. Some think the destroying angel that slew all the first-born is what is here intended; but this is distinctly mentioned in Psa 78:61. An angel or messenger may be either animate or inanimate; a disembodied spirit or human being; any thing or being that is an instrument sent of God for the punishment or support of mankind.