Revelation 9:3

What he saw was probably literal locusts (cf. Exodus 10:12-20). [Note: Newell, p. 129-32. Cf. Joel 1:6; 2:4-10.] Others have suggested that John saw modern instruments of warfare that looked like locusts. [Note: E.g., Hal Lindsey, The Late Great Planet Earth.] The Old Testament attests the destructive power of locusts (cf. Deuteronomy 28:38; 2 Chronicles 7:13; Joel 2:25). They often swarmed in apparently limitless numbers (cf. Psalms 105:34; Nahum 3:15). Joel likened what would come on the earth in the day of the Lord to a locust invasion (Joel 1-2). The locust is a symbol of destruction throughout the Old Testament (cf. 1 Kings 8:37; Psalms 78:46). Yet the locusts John saw had the power to hurt people as scorpions can, which normal locusts do not. They also had a leader (Revelation 9:11), which normal locusts do not (Proverbs 30:27). Probably these are demons who assume some of the characteristics of locusts. [Note: Moffatt, 5:406; Mounce, p. 194; Ladd, p. 131.] Spirit beings later appear as frogs (Revelation 16:13). A less literal interpretation has seen these locusts as "the forces of evil which are active in the world" and "memories of the past brought home at times of Divine visitation, which hurt by recalling forgotten sins." [Note: Swete, pp. 116, 118.]

"Should we assume the prophet saw something like a motion picture of the future in his vision and then attempted to explain it in terms of images he understood? Or did he see a picture precisely in the images he gives, images which paint reality rather than describing it? Which description of those options is ’more literal’? Is it the one that focuses on how it might look to us, so we explain what he meant in words and images very different from the prophet’s terms and images? Or should one focus on how it looked to the prophet and how it appears in the ancient text? We would thus attempt to understand his words in their literary character, both by examining the image in context and the Old Testament images and background(s) it evokes." [Note: Darrell L. Bock, "Interpreting the Bible-How Texts Speak to Us," in Progressive Dispensationalism, p. 91.]

The writer just quoted believed John saw locusts.