While the plant doesn't offer any nectar in its flower, it has this special way to secrete honeydew through these tiny (a couple of mm) nobs on its stems. The belief is that this attracts predators, especially ants, that will protect it. The plant can supposedly decide to make honeydew available when it wants to or not. I have watched some plants that rarely seem to have honeydew. This image, from last year, was from a plant that would put out the welcome sign mid-morning and remain open through late afternoon. Our meadow is very dry this year, and the Senna is wilting. As it is, our meadow is drier than it would prefer in a typical year. I suspect it might be having supply chain problems for candy production, but there are also fewer predators around. This is a Myrmica sp ant on Senna marilandica.