Which butterfly is a Silvery Blue?
- Left
- Right
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The Silvery Blue is on the right!
The Silvery Blue has an unmarked gray outer margin to their wing and bold black spots ringed in white on their submarginal line. They are primarily be out from the end of May to beginning of July in Vermont. You can find them near their host plants: legumes, especially our various vetch species, and they will nectar on lupine. The Silvery Blue prefer open, moist habitats but can be found in wooded areas as well. They are a northern species that has been spreading southward since at least the 1960s following vetch plantings along highways.
One particularly fascinating adaptation of the Silvery Blue is their relationship with ants. Females lay eggs on plants near a black ant nest. When the caterpillar hatches, they emit a pheromone chemical that summons and pacifies the ants, who then guard the caterpillar as it feeds. A threat from a predator elicits the release of mimic ant alarm pheromones. But the ants are not providing security services for free - the caterpillar emits a sweet, rich “honeydew” that the ants use for food.
The Northern Azure on the left has a greater range of host plants with some preference for heath shrubs like blueberry. While the Northern Azure can be identified from the Silvery Blue by the presence of dark markings at the margin of the wings and lack of distinct white ringed spots, the variation in wing patterning can be difficult to identify from other species like the Cherry Gall Azure and Spring Azure. This is in part because the field markings to identify the three species have not been resolved by experts. Read more about this dilemma from Bryan Pfeiffer’s article Getting the Blues. They typically fly from mid-May to mid-June.
Silvery Blue by Bruce Cook (iNaturalist)
Northern Azure by Kent McFarland (iNaturalist)
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