Caterpillars are the larval stage of moths and butterflies, a phase of rapid feeding and growth. They consume plant material, accumulating energy for transformation. During this period, caterpillars undergo several molts, shedding their outer skin as they increase in size. This stage is part of their complete metamorphosis, leading to pupa and adult forms.
Caterpillar Silk: A Fundamental Tool
Caterpillars do indeed produce silk, a versatile protein fiber. This silk is extruded as a liquid from specialized glands, known as labial glands or sericteries, located near their mouths. Upon contact with air, the liquid protein, primarily fibroin, solidifies into a strong and flexible thread. This material is distinct from spider silk in its origin and chemical composition, yet it serves as a highly adaptable construction material for caterpillars.
Purposes of Caterpillar Webs
Caterpillars utilize their silk for a variety of protective and functional purposes. Silk structures provide shelter from predators and harsh environmental conditions, such as extreme temperatures or rainfall. Many species construct silken shelters for safe spaces during molting. For moth caterpillars, silk is also used to spin cocoons for the pupal stage of their metamorphosis.
Beyond static shelters, silk also facilitates movement and escape. Caterpillars often lay down silken trails as they move, which can help them navigate and find their way back to a communal nest or food source. If disturbed by a predator, many caterpillars can drop from a leaf on a silk safety line, allowing them to suspend themselves safely away from danger and then climb back up. Some even use silk to manipulate leaves, rolling or tying them together to create concealed feeding and resting sites.
Diverse Web-Spinners in the Caterpillar World
The application of silk varies widely among different caterpillar species. Not all caterpillars construct large, communal webs; some use silk in more subtle ways, such as creating small silk pads for attachment or single strands for movement. For instance, many butterfly caterpillars create a silk pad to attach themselves before transforming into a chrysalis, which is their pupal stage, rather than spinning a full cocoon.
Prominent examples of web-making caterpillars include the communal tent caterpillars and fall webworms. Tent caterpillars build noticeable silken tents in the forks of tree branches, using these structures for communal living and protection, often leaving to feed and returning to the tent. Fall webworms, conversely, create extensive, looser webs that enclose entire branches, feeding within these silken enclosures. The domesticated silkworm, the larva of the Bombyx mori moth, is perhaps the most famous silk spinner, constructing a dense, single-strand cocoon that can be hundreds of meters long. Other species, like leaf-rolling or leaf-tying caterpillars, utilize silk to reshape leaves into personal, camouflaged shelters.