While I was taking photographs of the plant, I noticed some ants.
These kind of ants are called rover ants. They are not very big. What are they doing on the plant?
Here’s one in the flower. It is visiting the nectar-producing area or “floral nectary.”
The rover ants were also visiting an area under the flowers, on the sepals. Any ideas why?
Having some experience with cotton plants, I realized the ants were visiting some nectar-producing areas there as well. Nectaries outside the flower proper are called “extrafloral nectaries.” See that dimpled area the ant is facing? That is an extrafloral nectary.
As you can see, the extrafloral nectaries on the plant were very popular.
Many different plants produce nectar in various extrafloral nectaries and most of them attract ants and small wasps.
The most commonly-reported reason that plants have these structures is that the nectaries attract predators and parasites, which in turn attack the eggs and larvae of plant-feeding insects they encounter.
Have you ever seen ants visiting nectaries on plants? What kind of plant was it?
We got our package of lemon queen sunflowers (Helianthus annuus) in the mail, planted them and were pleasantly surprised when they started to grow like crazy.
This morning I’m happy to report the first bee. No, the flowers haven’t opened yet, but here is a tiny sweat bee resting on a leaf.
It is about the size of a pencil lead. It has been visiting nearby flowers. Can you see the pollen?
A parasitic wasp was also sitting on a sunflower leaf.
Are these insects merely resting in the warm sun?
A clue to what they may be doing comes from the black spots you see on the sides of the photos near the base of the leaves.
Those are ants.
What are the ants doing? Now, many people might think the ants are “eating the plants.” In a way the ants are, but not by chewing on leaves or harming the plant in any way.
It turns out sunflowers have extrafloral nectaries. As I explained in a previous post, extrafloral nectaries are structures on the plant in places outside of flowers that provide nectar for insects, often ants.
It is cold (for us) and windy this morning, and I wasn’t sure I’d be able to find a bug of the week. No fear, there’s always something going on in the insect world.
First I checked our barrel cactus, which is covered with yellow fruit.
As I got closer, I spotted a beige patch near the base of one of the fruit towards the right/center of the photograph. You’ll be able to see it more clearly in the next photograph.
The biege patch looked soft and furry, with some yellow and orangish bumps.
Ants were visiting those bumps in a purposeful way. First they would arrive looking slender.
After spending some time with their heads near the bumps their hind portion, called a gaster in ants, would start to swell up.
These ants are feeding at the extrafloral nectaries of the cactus. Nectaries are parts of a plant that produce the sweet juicy nectar. Many are found inside the flower of the plant. These structures are called extrafloral because they are outside of the flower.
Why does a cactus supply liquid sweets in the form of nectar to ants, especially in the desert where water is in short supply? There are several theories, including that ants increase the fertility of the soil around their mounds and ants are more likely to nest nearby when food is available, and/or that ants feed on insect pests while on the cactus. In any case, it is a fascinating example of just one of the complex relationships between ants and plants.
Thinking of sweets makes me want to have a cup of hot chocolate…