Azure Versus Eastern Tailed-Blue

Here are a couple small butterflies that can be distinguished, though not at a glance. It's one of our azures and an Eastern Tailed-Blue. This 2 butterflies are similar enough in appearance to suggest some level of relatedness, and they're in the same tribe. (A tribe is a taxonomic level between family and genus.) Let's take a minute to distinguish between these guys.

First I'll mention that butterfly watchers will sometimes give you a behavioral identification; if they see 1 of these butterflies flying low to the ground and only moderately fast, they'll identify them as Eastern Tailed-Blues. And if the butterflies are zippier and away from the ground, they're inclined to identify them as one of the azures. (Exactly which azure was a topic in another posting.)

While behavioral IDing might work a high percentage of the time, I have seen it fail too. You probably shouldn't argue with such an ID unless you get good looks at the butterfly when it's stationary.

So let's get to the stationary butterfly identification. Below is an azure, and you can identify it by what it lacks:

  1. The back wings don't have a little piece sticking out at the back, a feature called a tail even though it's actually just a part of the wing.
  2. And there are no small, orange, crescent-shapes on the back wing either. (This distinction you can only see when the wings are up and you can see the underside of the wings.)

June 15, 2023 at Sourland Mountain Preserve
Photo 300991654, (c) jpviolette, some rights reserved (CC BY-NC)

Next take a look at the Eastern Tailed-Blue. In this picture you should be able to see:
  1. A small projection sticking out of the back wing. (Okay, maybe you'll need to expand the picture to see it, but it's there.)
  2. And there are small, orange crescent-shapes on the back wing too.
While there are even more subtle differences in the wing patterns, why try and use subtle clues when the obvious clues are so much easier to see?

June 15, 2023 at Sourland Mountain Preserve
Photo 300992502, (c) jpviolette, some rights reserved (CC BY-NC)


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