Historically, only eusocial insects like ants, bees, and termites were thought to exhibit complex social organization and communication systems.

However, research since the late 20th century has found that E. lanestris, among a number of other phylogenetically related moth and butterfly species, demonstrates social behaviors as well.

Larvae spend nearly their entire development in colonies of about 200 individuals, and this grouped social structure offers a number of benefits, from thermoregulation to increased foraging success.

Landscaping practices like hedgerow cutting and intensive mowing destroy habitats and damage cocoons during pupation, leading to scattered populations and increased rarity.

Due to its preference for warm, dry weather, the small eggar has a more limited range, as it cannot function properly in the cold conditions found in the northern palearctic.

Host plants of the small eggar include blackthorn (Prunus spinosa), hawthorn (Cretaegus), and birch (Betula pendula).

E. lanestris prefers these plants due to their branching and twigging structure suitable for oviposition and larval tent construction (see below), along with the food resources they offer.

[6] Living in large groups may make larval colonies more apparent to visually-oriented predators, however this social structure has also allowed the small eggar to evolve a number of advantageous behaviors.

The exact mechanism by which larvae determine feeding times is unknown, but it likely has to do with the ability of the silk tent to transmit vibrations throughout the structure.

As caterpillars mobilize to leave the tent, others are alerted by the vibrations that it is time to feed, facilitating the movement of the entire colony, allowing for synchronous foraging.

However, by leaving the security of the tent en masse instead of solitarily, caterpillars are able to minimize their individual risk of predation and cooperate to locate and reach the best feeding sites.

During a synchronous foraging bout, larvae that are unsuccessful at first return to the tent and pick up fresh trails that were marked by a successful feeder.

In addition to indicating the best feeding sites, silk trails allow caterpillars to better grip the substrate over which they are traveling, which further increases foraging efficiency and success.

On sunny days when air temperatures may be lower than ideal, caterpillars congregate on the outer surfaces of the tent in direct sunlight.

The tent consists of layers of silk fibers that form air pockets which serve to insulate the nest and provide resting spaces for caterpillars inside.

Caterpillars form hard, brown, rounded cocoons, which are usually found concealed in low, dense vegetation of hedgerows and bushes, as well is in grass and brush.

[4] When females deposit eggs on the branches of their host plants, they secrete a protective cover of fluids and anal tuft hairs that hardens into a solid shell.

Birds prey on adult moths and have also been known to attack the tents in which larval colonies live and develop, which causes severe structural damage.

Reactions vary in severity, but typically present as an itchy rash that spreads from the area of contact and can develop red bumps and papules.

The moth's decreased abundance is attributed mainly to hedgerow trimming and intensive roadside mowing that directly harm the insect or destroy its host plants.