At the most basic level, I enjoy this photograph because the pink, green, and yellow colors are pretty to look at. The butterfly itself is clearly visible, but not immediately obvious, which adds a bit of interest. I also enjoy looking at the complex texture of the thousands of spines on the thistle leaves. I also framed and cropped this image to reveal a tall, narrow curve of the shape of the thistle flowers with the butterfly placed at the peak of the curve. This line serves to encourage the viewer to continue scanning up and down the image.
But, I also like this photograph because I just spent the past hour learning about monarch butterflies and thistle. I learned about the Mullerian mimicry between the monarch and the viceroy, and how it used to be believed to be a case of Batesian mimicry. That's what I learned as a kid, although I didn't know the term. I also learned that milkweed is the preferred food for the monarch, but it will eat thistle, too. The monarch population is declining rapidly, due in part to the decline of the milkweed population from herbicides. One study estimated a 90% decline in monarchs since 1996. And, I learned that thistle is classified as a noxious weed by the Maryland department of agriculture, and that various varieties of thistle are classified as pests by at least 35 states. I think this photograph shows Canada thistle. If I'm wrong, then it's most likely Bull thistle. Canada thistle is not native to Canada, or anywhere else in North America. It is native to the Mediterranean region and is believed to have been carried to North America by European colonists during the 1600s.