Verses with the word swarms in the Old Testament (4 verses):

Exodus 8:21
Else, if thou wilt not let my people go, behold, I will send swarms of flies upon thee, and upon thy servants, and upon thy people, and into thy houses: and the houses of the Egyptians shall be full of swarms of flies, and also the ground whereon they are.

Exodus 8:22
And I will sever in that day the land of Goshen, in which my people dwell, that no swarms of flies shall be there; to the end thou mayest know that I am the LORD in the midst of the earth.

Exodus 8:29
And Moses said, Behold, I go out from thee, and I will intreat the LORD that the swarms of flies may depart from Pharaoh, from his servants, and from his people, to morrow: but let not Pharaoh deal deceitfully any more in not letting the people go to sacrifice to the LORD.

Exodus 8:31
And the LORD did according to the word of Moses; and he removed the swarms of flies from Pharaoh, from his servants, and from his people; there remained not one.