What Is a Webspinner?

The insect

The insect: order Embioptera

Embioptera — commonly called webspinners or footspinners — is a small order of mostly tropical and subtropical insects, classified under the subclass Pterygota. The order has also been called Embiodea or Embiidina. More than 400 species in 11 families have been described, and it is estimated that there may be around 2,000 species alive today.

The name Embioptera comes from the Greek embios, meaning "lively", and pteron, meaning "wing" — "lively wings". It has not been considered a particularly descriptive name for this group of fliers; it may instead refer to their remarkable speed of movement, both forward and backward.

Every webspinner looks much the same: a cylindrical, long, narrow and highly flexible body, short sturdy legs, kidney-shaped compound eyes, no ocelli, and long thread-like antennae with up to 32 segments. Most are brown or black, some range to pink or reddish shades, and they measure roughly 15 to 20 mm (0.6 to 0.8 in) in length. The body form is completely specialised for the silk tunnels and chambers in which they reside.

Because the morphology is so similar between taxa, telling species apart is extremely difficult. For that reason, the main form of taxonomic identification used in the past has been close observation of the distinctive copulatory structures of males.

The trick that names them

Silk from their feet

The common name webspinner comes from the insects' unique tarsi on their front legs, which produce multiple strands of silk. In both males and females the legs are short and sturdy, with an enlarged basal tarsomere on the front pair containing the silk-producing glands. It is these silk glands on the front tarsi that distinguish the embiopterans.

The silk is produced in spherical secretory glands in the swollen tarsi of the forelimbs, and can be produced by both adults and larvae. Unlike silkworms and other silk-producing members of the Lepidoptera and Hymenoptera, which have only one pair of silk glands per individual, some species of embiid are estimated to have up to 300 silk glands — 150 in each forelimb. These glands are linked to a bristle-like cuticular process known as a silk ejector, and their exceedingly high numbers allow individuals to spin large amounts of silk very quickly, creating extensive galleries. The silk web is produced throughout all stages of the embiopteran lifespan, and requires modest energy output.

Webspinner silk is among the thinnest of all animal silks, being in most species about 90 to 100 nanometres in diameter. The finest of any insect are those of the webspinner Aposthonia gurneyi, averaging about 65 nanometres. Each thread consists of a protein core folded into pleated beta-sheets, with a water-repellent coating rich in waxy alkanes.

The gallery

Life in silk tunnels

The galleries produced by embiopterans are tunnels and chambers woven from the silk they produce. These woven constructions can be found on substrates such as rocks and the bark of trees, or in leaf litter. Some species camouflage their galleries by decorating the outer layers with bits of leaf litter or other materials to match their surroundings.

The galleries are essential to their life cycle: they maintain moisture in the environment and offer protection from predators and the elements while the insects forage, breed and simply exist. Webspinners only leave the gallery complex in search of a mate, or when females explore the immediate area in search of a new food source.

They continually extend their galleries to reach new food sources, and expand existing galleries as they grow. The insects spin silk by moving their forelegs back and forth over the substrate and rotating their bodies to create a cylindrical, silk-lined tunnel. Older galleries have multiple laminate layers of silk. Each gallery complex contains several individuals, often descended from a single female, and forms a maze-like structure extending from a secure retreat into whatever vegetable food matter is available nearby. The size and complexity of the colony vary between species, and can be very extensive in species that live in hot and humid climates.

Webspinners are gregarious, living subsocially in these galleries. Members of a colony are often related females and their offspring; adult males do not feed and die soon after mating. Males of some species have wings and are able to disperse, whereas the females remain near where they were hatched. Newly mated females may vacate the colony and establish a new one nearby. Others may emerge to search for a new food source to which the galleries can be extended, but in general the insects rarely venture from their galleries.

Two sexes, two fates

Males, females and wings

All females and nymphs are wingless, whereas adult males can be either winged or wingless depending on species. Where present, the wings occur as two pairs that are similar in size and shape: long and narrow, with relatively simple venation. They operate using basic hydraulics — before flight, chambers within the wings inflate with hemolymph, making them rigid enough for use; on landing, these chambers deflate and the wings become flexible, folding back against the body. The wings also have a crosswise crease, allowing them to fold forwards so the male can dart backwards without the wings snagging the fabric of the gallery.

The abdomen has ten segments, with a pair of cerci on the final segment. These cerci, made up of two segments and asymmetric in length especially in the males, are highly sensitive to touch and allow the animal to navigate while moving backwards through the gallery tunnels, which are too narrow to allow the insect to turn round.

The eggs hatch into nymphs that resemble small, wingless adults. After a short period of parental care, the nymphs moult a total of four times before reaching adult form. Adult males never eat, and leave the home colony almost immediately to find a female and mate. Those males that cannot fly often mate with females in nearby colonies, meaning their chosen mates are often siblings or close relatives. In some species the female eats the male after mating, but in any event the male does not survive for long. A few species are parthenogenetic, producing viable offspring without fertilisation of the eggs — reproductive security when a female cannot find a mate.

After moulting and mating, the female lays a single batch of eggs either within the existing gallery or after wandering away to start a new colony elsewhere. Because the females are flightless, their potential for dispersal is limited to the distance a female can walk.

Range and menu

Where they live and what they eat

Embiopterans are distributed worldwide and are found on every continent except Antarctica, with the highest density and diversity of species in tropical regions. Some common species have been accidentally transported to other parts of the world, while many native species are unobtrusive and yet to be detected. Some species live underground, or concealed under rocks or behind sections of loose bark. Others live out in the open, either swathed in sheets of white or blue silk, or hidden in less-conspicuous silken tubes, on the ground, on the trunks of trees or on the surface of granite rocks.

Largely restricted to warmer locations, webspinners are found as far north as the state of Virginia in the United States (38°N), and as high as 3,500 m (11,500 ft) in Ecuador. They were absent from Britain until 2019, when Aposthonia ceylonica, a southeast Asian species, was found in a glasshouse at the RHS Garden, Wisley.

The diet varies between species, with available food sources changing with habitat. Nymphs and adult females feed on plant litter, bark, moss, algae and lichen. They are generalist herbivores; during his research, Edward S. Ross maintained a number of species in the laboratory on a diet of lettuce and dry oak leaves. Adult males do not eat at all, dying soon after mating.

Most, if not all, embiopteran species are gregarious but subsocial. Typically, adult females show maternal care of their eggs and young, and often live in large colonies with other adult females, creating and sharing the webbing cover that helps protect them against predators. Maternal care starts with the placement of the eggs: some species attach batches of eggs to the web structure with silk, others form the eggs into rows in grooves excavated in the bark, others fix them in rows with a cement formed from saliva, and many bury them in a mass of silk. The majority guard their eggs, some actually standing over them. After hatching, mothers resume their gregarious behaviour, and in a few species parental care even involves feeding the nymphs with portions of chewed-up leaf litter and other foods.

Deep time

Evolution and fossils

Fossils of webspinners are rare. The group probably first appeared during the Jurassic; the oldest known, Sinembia rossi and Juraembia ningchengensis, both in a new family Sinembiidae created for them, are from the Middle Jurassic of Inner Mongolia and were described in 2009. The female of J. ningchengensis had wings, supporting Ross's proposal that both sexes of ancestral Embioptera were winged.

Species such as Atmetoclothoda orthotenes, possibly the first fossil member of the Clothodidae to be discovered — a family sometimes thought to be "primitive" — have been found in mid-Cretaceous amber from northern Myanmar. Litoclostes delicatus (Oligotomidae) has been found in the same locality. The largest number of fossils have been found in mid-Eocene Baltic amber and early-Miocene Dominican amber, and flattened compression fossils interpreted as webspinners have been found in the Eocene/Oligocene shales of Florissant, Colorado.

The external phylogeny of Embioptera has been debated, with the polyneopteran order controversially classed in 2007 as a sister group to both Zoraptera (angel insects) and Phasmatodea (stick insects). The internal phylogeny of the group is not yet fully resolved: a 2012 analysis by Miller and colleagues examined 96 morphological characters and 5 genes for 82 species across the order, and found four families robustly monophyletic — Clothodidae, Anisembiidae, Oligotomidae and Teratembiidae — while the status of Embiidae, Scelembiidae and Australembiidae remains uncertain. No single phylogenetic tree can be taken as definitive from that work.

Field notes

Webspinners in the wild

A few more faces from the order — pink, black, and one from Luzon.

The other meaning

Webspinner, the company: why the name

Webspinner is a company based in Portland, Oregon. It builds AI you own outright instead of renting — sovereign AI that runs on home-office hardware, under your control, on your desk. It also offers a free course that has anyone build a working language model in an afternoon.

The name is not decoration. A webspinner is an animal that spins its own silk from its own body and builds and extends its own world — a gallery it lives in, maintains, and grows as it grows. That is the model for the company's work: AI you create and own, rather than AI you subscribe to and inhabit. The insect does not rent its tunnel. It makes it.

Learn more at webspinner.com.

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