Why do neuropteran larvae have jaws that form a sucking tube?

In neuropteran larvae, the jaws are specialized to function as a sucking tube to facilitate their carnivorous diet. Because these larvae lack a true mouth, they must ingest liquid food directly into the pharynx.1

The sucking tube is formed by the mandible positioned above and the maxilla below; these two structures fit together but remain separable. By using a pharyngeal pump, the larva sucks the internal contents out of its prey, typically leaving behind only a hollow skin. This adaptation is a defining feature of the order Neuroptera, distinguishing them from related groups like Megaloptera and Raphidiodea, which possess more conventional mandibles.123