The natural world contains many creatures with remarkable abilities, and among the most intriguing are those known for producing silk. These “web spinners” encompass a diverse group of organisms that share the common trait of creating intricate structures from a protein-based fiber. This skill allows them to build shelters, capture food, and even travel.
What are Web Spinners?
The term “web spinner” most commonly refers to two distinct groups: the insect order Embioptera and, more broadly, spiders. Embiopterans, often called true webspinners or footspinners, are small, soft-bodied insects primarily found in tropical and subtropical regions. They are unique among insects for having silk glands located in the swollen tarsi (lower leg segments) of their forelimbs, allowing adults and larvae to produce silk. These insects are gregarious, living in subsocial colonies within their silken galleries.
Spiders, conversely, are arachnids, distinguished by their eight legs and the presence of spinnerets on their abdomen for silk extrusion. While all spiders produce silk, not all spin webs for prey capture. Unlike Embiopterans, spiders utilize a wider array of silk types and spinning behaviors. There are over 53,000 recorded spider species, inhabiting nearly every land habitat globally.
The Science of Silk Production
Silk production in web spinners involves specialized biological mechanisms. In Embiopterans, spherical secretory glands within the forelimbs produce the silk. Some species possess up to 300 silk glands, with 150 in each forelimb, enabling rapid and extensive silk creation. This silk, composed of a protein core folded into pleated beta-sheets, is thin, ranging from 90 to 100 nanometers in diameter, and features a water-repellent coating.
Spiders produce silk from multiple types of glands, each connected to a spigot on their spinnerets at the posterior end of their abdomen. There are at least six distinct types of silk glands, each yielding a different silk with specialized properties. The liquid protein hardens into a fiber not by exposure to air, but through the mechanical drawing process, which alters its internal structure. Spider silk exhibits strong mechanical properties, combining high tensile strength with extensibility, allowing it to absorb energy before breaking.
Diverse Uses of Silk Webs
Web spinners utilize their silk for a variety of purposes. Spiders employ their silk for capturing prey, constructing sticky webs. Beyond hunting, silk provides shelter, including retreats and egg sacs. Spiders also use silk for reproduction, creating sperm webs, and for wrapping prey to feed their young. Some young spiders use fine “gossamer” threads for dispersal, a process known as ballooning.
Embiopterans, or true webspinners, primarily use their silk to construct tunnels and galleries. These woven structures provide shelter and protection from predators like centipedes, and maintain temperature and humidity levels. These tunnels also facilitate foraging within their colonies, with some species camouflaging their galleries with leaf litter or other materials.
Web Spinners in Their Environment
Web spinners inhabit a range of environments across the globe. Embiopterans are predominantly found in tropical and subtropical climates, often residing in soil, under bark, or within leaf litter, in humid, warm conditions. Their silk tunnels can be observed on surfaces like rocks and tree bark. These insects play a role as detritivores, feeding on dead plant material, moss, lichens, and sometimes epiphytic algae.
Spiders, on the other hand, are adaptable and have established themselves in nearly every terrestrial habitat. Their ecological roles are diverse; many are predators, contributing to insect population control. The widespread presence and varied functions of silk production underscore the roles these creatures play in maintaining the balance of ecosystems.