Small Eggar

Small eggar moths have a wingspan of 30–40 millimeters, and females are generally larger than males. Male and female adults have a gray-brown to reddish coloration with white spotting on their upper wings, however males tend to have darker, grayer coloration than females. Additionally, males antennae are bipectinate, or feather-like. Both sexes have setae on their bodies, but females have an extra grayish tuft of hair at the base of their abdominal region. Larvae are black and hairy, developing red coloration during the later larval stages. They can reach lengths of approximately 50 mm and often have yellow coloration along the sides of their bodies throughout development.

E. lanestris is found in scattered, patchy populations across the palearctic region, with most of its documentation in England, Ireland, and Wales. 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. The moth is only active from spring to mid-summer in the temperate region of the U.K. and Ireland.

E. lanestris is a highly social insect, particularly during its larval stages. Hence, small eggar larvae are categorized as gregarious caterpillars. 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.

Synchronous foraging. One benefit of the grouping behavior found in E. lanestris is increased foraging efficiency, which they achieve by foraging together in a large group. Colonies of caterpillars feed several times a day, leaving their tent as a group in search of food. 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. Unlike many nocturnal foragers, E. lanestris feeds both during the day and at night, so it runs the risk of detection by visually-oriented predators during daytime foraging forays. …

The small eggar only feeds during its larval stages of development, consuming leaves of blackthorn, hawthorn, and birch. Due to their high water and nitrogen content, young leaves, rather than more mature ones, are preferred by caterpillars. Caterpillars hatch around the time of leaf emergence in order to maximize feeding while leaves are still young and nutritious. The small eggar is a central-place forager, meaning it returns to the same nesting site after each foraging trip. This allows colonies of larval E. lanestris to communicate where the best feeding sites are located. However, as colonies develop, the closest food resources become too mature or are depleted, so caterpillars must venture further and further from their central site to feed.