Eucheira socialis, commonly known as the madrone butterfly is a lepidopteran that belongs to the family Pieridae.

Locally known as Mariposa del madroño or tzauhquiocuilin, it is endemic to the highlands of Mexico, and exclusively relies on the madrone (Arbutus spp.)

The species is of considerable interest to lepidopterists due to gregarious nest-building in the larval stages, and heavily male-biased sex ratio.

The adults have a black and white pattern on their wings, and the males are generally much smaller and paler than the females.

[4] The larvae do not undergo diapause and continue to feed and grow communally in the coldest months of the year.

[4] The distribution of E. socialis is restricted to the highlands of Mexico at elevations of 1,800 m (5,900 ft) in madrone habitats.

[4] Characteristic of all lepidopterans, E. socialis are holometabolous and go through four distinct developmental stages namely egg, larva, pupa and adult.

[4][5] The eggs are bluish-white and are laid in clumps on the underside of the host plant Madrone in the month of June–July.

The larvae then build their first communal nest by folding these consumed leaves and securing them with silken strands.

The larvae are a bright green and mildly fuzzy when they hatch, but turn brown and less pubescent as they grow.

[6] Despite extremely low temperatures in the winter, the larvae do not undergo diapause, and continue to feed and grow throughout the year.

It is speculated that the ovipositional behavior of the females has been under strong selection in the past to maximize social interaction among larvae.

The freshly hatched larvae forage and rest together, and aggregate in a loosely woven tent-like silk structure over the surface of the leaf.

[4] By the end of the growing season the nest walls can be thick enough to resist tear and hold water.

The nest plays an important role in thermoregulation by providing a cool shelter for the larvae on sun-intensive days.

[9] Therefore, it is proposed that communal nesting behavior evolved initially due to kin-selection, facilitated by a single oviposition event leading to an egg mass with high-relatedness.

But the maintenance of this behavior among non-kin could be due to high benefits of communal nesting such as predator avoidance and thermodynamic efficiency.

They feed gregariously on the leaves of the host plant until the early hours of morning, and return to the nest before sunrise.

[7] The nocturnal foraging is thought to be an evolutionary response to avoid day-active parasitoids, and predators such as birds and social wasps.

The high differentiation among sub-populations is thought to have been caused by weak adult dispersal, and patchiness of madrone habitats due to their restriction to higher elevations.

Such a ratio is thought to be evolutionarily maintained because of the selective advantage of male-biased groups in the communal nests.

Even though the days are much warmer than the nights in the winter, the caterpillars remain aggregated in their nests and venture out to forage strictly after sunset.

The oviposition of the eggs on the underside of the leaves, and nocturnal foraging of larvae decrease exposure to predators and other parasitoids.

[4] The silk nests built by the larvae are believed to have been used in the past for making a paper-like fabric[13] and small boxes.