What does Exodus 10:15 mean?
Egypt was threatened with an eighth plague (Exodus 7:21; 8:6, 17, 24; 9:6, 10, 24) if their king still refused to free the Hebrews slaves (Exodus 1:11–14; 10:4–6). Scripture now describes what happened when this unimaginable cloud of insects arrived (Exodus 10:14). The claim that there was nothing "green"—meaning not a single uneaten stalk or leaf—fits with the behavior of large locust swarms.Locusts are a phase of common grasshoppers. Under certain conditions, they breed a generation with a slightly different appearance and drastically different behavior. Normal grasshoppers prefer to be alone. Their locust form is compelled to close grouping, is much more aggressive, eats more, and breeds faster than the standard version. A "small" swarm of a square kilometer, or less than one half of a square mile, can eat as much every day as thirty-five thousand people. As vegetation is consumed, locusts will eat virtually anything they can chew. In extreme cases, that has included leather, fabric, softer woods, paint, and the corpses of fellow locusts.
Locust devastation of crops is disastrous. Yet major swarms create many other problems. A locust's bite is not dangerous, but it is painful and irritating. The insects make a loud, raspy buzzing noise in addition to the sounds made when flying and bumping into things. They produce waste that contaminates food and water. Since they fly and land everywhere, those who are crushed leave a mess, in addition to the bodies of those who die. They invade buildings and homes, bringing all the same problems.
A late-nineteenth century locust plague in North America was estimated to cover an area the size of California. That nation-sized cloud was estimated to contain as many as twelve trillion insects: twelve thousand million locusts. Here in the book of Exodus, Egypt faces a swarm so dense and wide that it blocks out the sun and covers every surface. The insects also get into homes, polluting and eating everything inside. The only other biblical account similar to what happens in Egypt is found in a combination of prophecy and history recorded in Joel chapters 1 and 2 (Joel 1:4, 7, 13–20).
Pharaoh's advisors were already terrified to face a locust swarm (Exodus 10:7) after hail destroyed so many crops (Exodus 9:31–32). This is even worse than they imagined. It's no surprise that the king scrambles to correct his mistake (Exodus 10:16–17).