The eighth plague of Egypt was locusts. Before the plague, God informed Moses that from that point on He would "harden Pharaoh's heart," (as promised earlier in 4:21) so that Pharaoh would not give in, and the remaining miracles (the final plagues and the splitting of the sea) would play out.

As with previous plagues, Moses came to Pharaoh and warned him of the impending plague of locusts. Pharaoh's officials begged him to let the Hebrews go rather than suffer the devastating effects of a locust-swarm, but he was still unwilling to give in. He proposed a compromise: the Israelite men would be allowed to go, while women, children and livestock would remain in Egypt. Moses repeated God's demand that every last person and animal should go, but Pharaoh refused.

God then had Moses stretch his staff over Egypt, and a wind picked up from the east. The wind continued until the following day, when it brought a locust swarm. The swarm covered the sky, casting a shadow over Egypt. It consumed all the remaining Egyptian crops, leaving no tree or plant standing. Pharaoh again asked Moses to remove this plague and promised to allow all the Israelites to worship God in the desert. As promised, God hardened Pharaoh's heart, and he did not allow the Israelites to leave.