Speaking of Nature: A quick lesson on butterfly anatomy: Inspecting the gray hairstreak, an unexpected treat
Published: 08-29-2023 2:53 PM |
By the time you read this column, my summer break will officially be over. It has been an eventful summer for me with new birding records being set in both July and August (more on that next time) and I have taken thousands of nature photos that will now have to be sorted and filed in the cold months to come. Capturing the essence of the season is not always an easy thing to do, but I have a photo today that I think will do the trick.
Here is the setting: It is a warm sunny day in August and the sounds of crickets fill the air. There are birds around, but they are very quiet. Only the finches really seem to have much work to do as they try to feed their chicks and the excited, demanding calls of young American Goldfinches adds a rhythmic counterpoint to the slow droning of the insects. There is a lovely breeze blowing and I am standing in front of an untamed natural garden of wildflowers.
The soil here is shallow and rocky and the plants are weedy and bright. Fleabanes, asters, knapweeds and members of the mint family are the most numerous. I see none of the crickets that continue to sing, but I do see many bumblebees and several different species of wasps that are visiting the different blossoms. There are so many individual insects that it is difficult to choose which one to focus on, but that all changes with the arrival of a very beautiful butterfly.
This particular specimen is an example of a gray hairstreak (Strymonmelinus) and it would be generally described as “small.” The problem with this description is that it is rather vague, so let me give a quick lesson on butterfly anatomy. I am going to focus on the wings, of which there are four.
On each side of the body there is a “forewing” and a ”hindwing.” When the butterfly opens its wings, we will tend to see the forewing most prominently, but when the butterfly has its wings closed (as in this photo) we will see the hindwing most prominently.
Since there is never any guarantee about how any one particular butterfly will be viewed, it is not always fair to discuss wingspan. The easier measurement to talk about is something called the “costal margin.” In layman’s terms, this refers to the leading edge of the forewing. In the case of the gray hairstreak, the costal margin is 10/16 inches. This, I think, is worthy of the small category. The flowers that this hairstreak is so intently working on appear to be those of a plant called a bugle (Ajuga reptans). Each of the individual blossoms is about 1/2 inch in length and you will notice that a slender “stamen” projects out beyond the upper lip of the irregular flowers. Stamens are those portions of a flower that support the pollen-producing “anthers” and you can imagine that no butterfly will be able to encounter a bugle flower without picking up some pollen. This is the great trade upon which all flower-pollinator relationships are based; I give you food and you transport my pollen to the next plant.
Although I would characterize this particular individual as “uncooperative,” there did come a moment when it struck a perfect profile pose. I snapped a picture and now we can examine all of the field marks of a gray hairstreak. On top of the head (between the eyes) there is a small patch of orange.
Along the first 1/3 of the costal margin there is a faint frosting of the same orange color. The forewing has a band of delicate black and white marks that cross each cell of the wing. But the real show starts on the hindwing.
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Notice that the black and white markings are bolder on the hindwing. Also notice that there are hints of that orange with them as well. Together, these are the lines for which the “hairstreaks” get their name. On the outer edge of the hindwing we see two orange spots with smaller black spots inside them. The exact size of the black spots can vary from one individual to the next, but they are standard markings.
And finally, we come to those gorgeous filaments extending from the outer margins. They almost look like a second pair of antennae. This individual is a female. Males have orange on their abdomens.
I can’t believe how quickly I have run out of room, but there are a few last details that I want to share.
Gray hairstreaks will feed on a wide variety of flowers, but the females prefer to lay their eggs on legumes. In western Massachusetts, this means clovers and trefoils. Since these are both very common plants there is still time for you to find a gray hairstreak of your own. Just make a picnic in a lawn that has been unmowed for a week and look for these beautiful little butterflies around the clovers. I can’t really think of a nicer excuse to sit in the sun and enjoy the sounds of late summer.
Bill Danielson has been a professional writer and nature photographer for 26 years. He has worked for the National Park Service, the US Forest Service, the Nature Conservancy and the Massachusetts State Parks and he currently teaches high school biology and physics. For more in formation visit his website at www.speakingofnature.com, or go to Speaking of Nature on Facebook.
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