Partridge pea is a small flower which is native to the tallgrass prairie areas of Iowa. Unlike most of the tallgrass prairie species, partridge pea is doing quite well, and can be found in moderately wet areas all over the state.
Partridge pea is typically about a foot and a half high, but I have seen some plants that were at least four feet high in an unusually wet year. It looks a lot like the domestic house plant which is called "sensitive plant", and in fact has some of the same characteristics. It has little rows of leaflets opposite each other, which fold up to touch each other at night. It is an annual plant, and has spectacular yellow blooms in late July.
On a nature walk I was on one time, a botanist friend pointed out to me that this flower has extrafloral nectaries. A nectary is a place on a plant that gives nectar. "Extrafloral" means that it is not a part of the flower. Therefore, an extrafloral nectary is a place on the plant, away from the flower, that gives out nectar.
Many plants have extrafloral nectaries. Scientists think that they are present in order to attract ants. The ants crawl all over the plant, and take the nectar whenever it is doled out. In the process, they attack all kinds of small insects that might be present on the stems and leaves. The plant therefore gains some measure of protection from insects which might eat the leaves otherwise.
I spent some time observing partridge pea and its ants. I found that in certain areas, all partridge pea plants had several ants present at all times. In certain other areas, there were no ants to be found. When there were no ants, a large variety of insects visited the nectaries. When there were ants, the insects that visited were not as successful, but I still saw a small fly that was able to steal nectar by distracting the ants, and then flying around to the nectary. That fly could be called a nectar thief.