Mournful Duskywing

The spherical eggs are laid on the terminal end of a hostplant. While initially yellow, the eggs will turn deep orange with maturation. Rather than being laid in clusters or groups, females will lay their eggs singly in separate locations. Once the egg progresses to the larval stage, the larvae are gray-green, covered with white spots throughout its body, and has lateral yellow stripes. The head has a brown coloration. The pupa are gray-green and are hairy. The majority of the vestiture on the wings of the adults consists of primarily a brown coloration, with black spots on the part of the wing closer to the body. Adults have scales with a white coloration on the fringe of their hindwing that distinguishes them from most butterfly species. This white coloration typically reaches to the base of the scale. Its appearance is similar to Erynnis funeralis, which is the only other species of the Erynnis genus that also has a white fringe on the hindwing. Furthermore, Erynnis funeralis and Erynnis tristis significantly overlap in spatial distribution in California and Arizona. However, Erynnis funearlis has a longer and more narrow forewing than Erynnis tristis. Erynnis funeralis typically grows to a wing span size of 33 to 38 mm, while adults of Erynnis tristis are 28 to 31 mm in length. …

E. tristis prefers forest clearings and oak woodlands. E. tristis has an urban presence as well, representing its adaptation and flexibility to human disturbances. In Palo Alto, E. tristis was observed frequenting primarily open-space recreation areas, with a smaller presence in nature preserves and office parks. This represents a disconnected distribution in the urban gradient, where E. tristis was not found in residential areas or golf courses.

The butterflies practice the hill-topping mating system, in which males will wait on various perches for receptive females to mate with. The males have been observed perching on various plants, including foothills paloverde (Parkinsonia microphylla), barrel cactus (Ferocactus wislezni), and creosote (Larrea tridentata). Though the perches are commonly plants and shrubs, males have also been observed perching on boulders as well. The butterflies have been observed periodically flying around the perch and landing at the area prior to the flight. Males will leave their perch either to pursue passing butterflies, or to chase rival males in a competition for the perching location. The interaction with two males includes a descending flight to the ground, where the butterflies turn about one another. The butterfly lower to the ground will fly away from the other male and the perching location. With a receptive female, the male will fly behind the female. Subsequently, the two will then land and mate on the ground. In contrast, females that reject the male's advances to mate will fly vertically. It was observed that 98% of the females at the perches are virgins, indicating that the females visiting the perches primarily do so to mate. …