Within the last twenty years, researchers have made several discoveries involving the butterfly genus Celastrina, the azures. Several years ago, there was only one recognized species in the eastern United States, the Spring Azure (Celastrina ladon). Now that scientists can look at DNA sequences, it has become clear that there are several distinct species in this region. As I have mentioned in previous posts, there are five species that are commonly found in eastern Pennsylvania. The Northern Spring (Lucia) Azure (Celastrina lucia) is the first azure to appear in spring. This species is most common in the mountains from the Kittatinny Ridge and north from there. The Northern Spring Azure primarily eats the leaves and stems of blueberries (Vaccinium) as caterpillar.
The second species to emerge in spring, often in the first week of May, is the Spring Azure (Celastrina ladon). Almost identical to the previous species, the Spring Azure is the common azure for the first few weeks of May. In the Lehigh Valley, which is located south of the Kittatinny Ridge, this seems to be the predominant azure species. The Spring Azure's primary caterpillar food plant is flowering dogwood (Cornus florida), a common tree of deciduous forests.
Beginning around the third week of May, a new batch of azures can be found in the woods and forest edges. At this point, many Spring Azures are worn and dull, as they have been flying for a few weeks, so they can be separated from these new Cherry Gall Azures (Celastrina serotina). This species uses Wild Black Cherry (Prunus serotina).
The longest-lasting of the azures is the Summer Azure (Celastrina neglecta). This species is the most distinct of any of the species already mentioned. The spring species are usually well-marked with dark spots, but Summer Azures are often very very pale and chalky white rather than blueish gray. As a caterpillar, the Summer Azure may use several shrub species including silky dogwood (Cornus amomum) and meadowsweet (Spiraea latifolia). Since these plants are commonly found along woodland edges and brushy fields, this butterfly is often found in these habitats rather than woodlands.
The fifth and rarest species is the Appalachian Azure (Celastrina neglectamajor). This large, pale azure flies at the same time as the Summer Azure, but only feeds on black cohosh (Actaea racemosa; syn. Cimicifuga racemosa). The female Appalachian Azure lays her eggs on the unopened flower spikes of this cohosh. Once the caterpillar hatches, it feeds on the flower buds and stems (Pavulaan & Wright, 2000).
In Pennsylvania, this species is primarily found in the southern half of the state. A few years ago, I learned that this species had never been found in my home county. After learning this, and after finding a large patch of the host plant, I kept an eye out for any azures in that area. In 2009 and 2010, I checked the plants for eggs and caterpillars, but was unsuccessful. This year was different. While I was in the woods, I spotted an azure flying just above my head. I followed the azure in an attempt to get a better look. I followed the blue speck until it led me to the patch of black cohosh and finally landed--on the host plant for the Appalachian Azure. Until this point, I had assumed that this was another one of the ubiquitous Summer Azures. I immediately checked the flower spike of the closest cohosh plant. Sure enough, I found two azure eggs situated between the flower buds! This was the first sighting and documented record of Appalachian Azure in Monroe County, which could be a sign of range expansion since these butterflies were not observed at this location in previous years. In the next week or so, I hope to return to the patch of cohosh and count the number of eggs present and hopefully get photos of adults and caterpillars.
Pavulaan, Harry and David M. Wright. "The Biology, Life History, History, and Taxonomy of Celastrina neglectamajor (Lycaenidae: Polyommatinae)." The Taxonomic Report. 2.5 (2000): 1-19. pdf.