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(leaf-cutting bees and their allies), a family of insects of the order Hymenoptera. Unlike other bees, megachilids have a special pollen-collecting apparatus in the form of a dense brush of hairs on the lower abdomen. The females build their nests in the ground or in the hollow stalks of plants. The burrow is lined and partitioned into several cells with oval pieces of leaves, which the bees have cut with their jaws and have joined together with sticky secretions. A supply of food, consisting of a mixture of nectar and pollen, is placed in each cell, and then an egg is laid. Megachilids pollinate many plants. They cause some damage to leaves, however.