The Madrone Caterpillar (Eucheira socialis)
      (Pieridae)
 

Overview

Trail Making and Foraging Behavior

Shelter Building and Thermoregulation

References

Overview

The madrone caterpillar is found in the high mountainous regions of Mexico where its host tree, the madrone (Arbutus) occurs. The caterpillars are present from early summer unit late the following spring.  The caterpillars that comprise a colony, which may number 200 or more, are siblings and they remain together throughout their lifetime, pupating and eclosing to the adult en masse. The larvae construct a silken, bag-like nest, within which they rest between bouts of feeding.  Adults emerge from an opening at the bottom of the nest in June. Recent studies indicate that some populations of the caterpillar are strongly gender biased with as many as 80% of the caterpillars being male.
 
 
 
 
 

Trail Making and Foraging Behavior

Eucheira caterpillars leave their nest to feed only under the cover of darkness. The caterpillars become active soon after darkness sets in in the early evening. They follow silk trails to distant feeding sites, where they forage throughout the night and early morning, typically returning to the tent just before sunrise.  In the winter, the catepillars forage at very cold temperatures and are able to remain active even when temperatures hover about 0^oC.  Occasionally the caterpillars are immobolized by sub-zero overnight temperatures and can not return to the bolsa until the sun comes up and warms their bodies.

The larvae of Eucheria mark their trails with a pheromone secreted from the tips of their abdomens and, like tent caterpillars, are highly responsive to 5b-cholestane-3-one.  Unlike tent caterpillars, however, the madrone caterpillars do not recruit to food-finds.
 

Shelter Building and Thermoregulation

The caterpillars construct their shelter entirely from silk.  The walls of the nest are so densely woven that the nests will hold water and can only be penetrated with a sharp knife. There is usually only one exit hole which is found at the bottom of the structure. The nests trap the heat of the sun and warm to temperatures in excess of the ambient temperature.  The caterpillars move about the nest adjusting their body temperature by seeking warmer or cooler areas.  In the winter, studies indicate that the caterpillars may keep their body temperatures relatively cool during the day to prevent adaptation of their enzyme systems to warm temperatures. Such adaptation would hinder their ability to locomote on cold evenings.  Occasionally, the caterpillars are immobolized by sub-zero overnight temperatures and can not return to the bolsa until the sun comes up and warms their bodies.
 
 

Fitzgerald, T. D. and D. L. Underwood. 2000. Winter foraging patterns and voluntary hypothermia in the social caterpillar Eucheira socialis. Ecological Entomology 25:1-10.

Fitzgerald, T. D. and D. L. A. Underwood. 1998. Trail Marking by the larva of the Madrone butterfly Eucheira socialis and the role of the trail pheromone in communal foraging behavior. J. Insect Behavior 11:247-263.

Fitzgerald, T. D. 2001. Night Life of Social Caterpillars. Natural History Magazine 110: 38-42

Underwood, D. L. A. and A. M. Shapiro. 1999. Evidence for division of labor in the social caterpillar Eucheira socialis  (Pieridae: Lepidoptera). Behav. Ecol. and Sociobiol. 46: 228-236.

Underwood, D. L. A. and A. M. Shapiro. 1999. A male-biased primary sex ratio and larval mortality in Eucheira socialis  (Pieridae: Lepidoptera). Evol. Ecol. Res. 1: 703-717.