Hey Ducks - What's Under Those Leaves?

For some reason the ducks are in a foraging frenzy. All winter, they have shown little or no interest in foraging. Now, after a few warmer days, something -- bugs, worms, grubs? -- must be coming to life under the fallen leaves and dead crabgrass. I don't have a clue what it is, but they cannot be distracted from their mission. I hope this means they will start laying again.