These medium sized moths of the family Lasiocampidae exhibit sexual dimorphism, with the males being smaller with stubbier forewings. The males tend to be a darker reddish brown, and the females tend toward a reddish tan. Both sexes are darker in the medial area and have a simple pattern with slightly curved postmedial and antemedial lines, and no spots. The easiest way to differentiate Malacosoma californicum from M. disstria is that on M. californicum the transverse lines have a pale element outside the medial area, whereas the lines on M. disstria are uniformly dark. And in Malacosoma constrictum, which is only found near oaks, the forewing is a uniform color, as are the transverse lines.
Western Tent Caterpillar Moths can be found in wooded areas region wide. The larvae are generalists, feeding on the leaves of at least 15 genera of hardwood trees. During their first instars they live communally in their eponymous tents. This helps protect them from predators (safety in numbers) and may aid in thermoregulation. But during the last instars when their caloric needs are highest they are solitary eating machines. Occasionally large outbreaks occur, which may result in defoliation of trees, but the damage is seldom fatal to the tree. Adults do not feed and only live a few days after eclosure, which is usually in July and August.
https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5303047.pdf
Size- FW length 10-12mm in males, 15-19mm in females
Habitat- Deciduous woodlands
Range- Region wide
Eats- Larvae eat a wide variety of leaves; adults have only vestigial mouthparts and do not feed
Flight Season- July-August