Mature larch sawfly drop to the ground and spin cocoons in the moss or duff. The ground snrface of tamarack bogs is usually uneven, and the moss is variable in moisture content. During hot dry weather the moss on the tops of hummocks in dry sites becomes dry, while that in the depressions remains moist. During periods of heavy rain, or in wet sites, the depressions may be filled with water, while the hummocks usually remain above the water.