How do caddisfly larvae make silk underwater?

Caddisfly larvae produce silk using specialized glands located on their lower lip, known as the labium.1

This silk is used by various species to construct protective structures, such as tubular cases, webs for catching food, or protective lairs. When building cases, the larvae often incorporate materials like sand grains or vegetable debris into the silk to provide additional rigidity and protection. Because these glands function underwater, the larvae are able to spin these protective coverings directly within their aquatic environments.1