Sugar Fix

I noticed that this trumpet vine (Campsis radicans, Bignoniaceae) was covered with ants the other day. Ants are usually on plants for one reason and that is to get a sugar fix.

Often they are getting their fix from aphids or other herbivorous insects that produce honeydew (see a video here). Sometimes they are getting the sugar from the flowers of the plants in the form of nectar, just like bees, butterflies, and hummingbirds do. You can see clearly in this photo that they are entering the flower's corolla to access the nectar inside. There is, however, another way for ants and other insects to obtain nectar from flowers.

As you can see, the ants are also foraging on unopened flowers and flower buds. This is because trumpet vines, like a surprising number of other plants, produce nectar in special glands outside of the flowers. These glands are called extrafloral nectaries. They are the little circular structures seen here on the calyx of the flower.

Extrafloral nectaries produce nectar that is attractive to a variety of insects, most of which are beneficial to the plant by defending it from its enemies.
The next time you see ants on a plant in your garden don't just assume that they are harming it. A closer inspection may reveal that they are actually defending it. If you see them tending aphids though, there may be cause for concern!

Yikes!