Ants and Plants

Sometimes we get so used to seeing ants visiting extrafloral nectaries, it seems unexpected to see them visiting regular floral nectaries.

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Take this shrubby dogwood flower (probably gray dogwood, Cornus racemosa). The nectaries are the creamy yellow bands at the base of the female part of the flower (the pistil or carpel) in the center.

 

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Formica workers seemed to be visiting the plants most frequently, although other ants were in the area.

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Ants weren't the only insects attracted to the nectaries of the dogwood flowers.

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Along with the usual wasps, flies and bees, there were also more unusual true bugs and beetles.

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A number of the smaller butterflies stopped by, including hairstreaks and blues.

It turns out azure butterflies in particular are attracted to these types of dogwoods and lay their eggs on them. What happens next? Of course, the ants tend the azure caterpillars! Nature Posts blog has an incredible series of photographs and videos of ants tending azure butterfly caterpillars.

Interested in planting a garden for ants or butterflies? You might want to consider planting some of the dogwoods (Cornus sp.)

Have you ever seen azure caterpillars on dogwoods? I am definitely going to be looking from now on.

 

Have you ever been on the quest for something and discovered something else entirely?

Take my pursuit to capture a "calendar-perfect" photograph of ants visiting peony buds. People have known that ants tend extrafloral nectaries on peony buds for a long time. It is one place that you are sure to find ants sitting relatively still (for ants) out in the open. Taking some colorful photographs of ants posing on peony buds seemed much easier than trying to capture one scurrying on the ground.

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As I was looking through the shots, I began to notice something else.

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It was subtle at first, but it's there if you look for it.

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The one on the left will give you a big hint.

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Here's one on a peony flower.

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See it now?

 

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It seems like ants on peonies have more than their share of dents and missing body parts. If they were cars, you'd be sending them to the body shop.

I think it is conventional wisdom that foragers are the older ants in the colony and that older ants are probably more likely to be beat up a bit. It is possible, however, that tending peony buds is extra risky. What do you think?

Do you have a photograph of a "dented" ant? Leave us a link in the comments or share it on our Facebook page (No fair creating the dents yourself).

Did you recognize the big yellow flower from the Wordless Wednesday post with the carpenter bee? This might give you a hint:

It was from a luffa or sponge gourd, Luffa aegyptiaca (previously named L. cylindrica.)

Why were the ants on the underside of the flower in the last photograph of that post? It turns out that the luffa plant has been crawling with rover ants, even before it started to flower.

For a clue, let's look at the underside of the luffa leaves. What are those green bumps on the leaf surface between the veins?

You might wonder if they are the leaf openings called stomata, but the stomata are the smaller dots.

Close up the bumps look like tiny green volcanoes.

Those are extrafloral nectaries, or EFNs. Extrafloral nectaries are nectar-producing glands found in areas of the plant outside of the flowers. Extrafloral nectaries occur in at least 66 different plant species and vary in size, shape and placement. The type of found in luffa are called "button-shaped."

Like the nectar produced in the floral nectaries, extrafloral nectar is a liquid solution of sugar in water, with trace amounts of amino acids. The nectar attracts many different kinds of insects, but ants are often the most common visitors. The ants often chase away or capture plant-feeding insects, thus protecting the plant.

This means we can add luffas to the list of plants that might be useful for gardening for ants.

For more information, see:

Vivek Mohan Agarwal and Neelkamal Rastogi. 2010. Ants as dominant insect visitors of the extrafloral nectaries of sponge gourd plant, Luffa cylindrica (L.) (Cucurbitaceae). Asian Myrmecology, 3, 45–54. (free .pdf available at the "Read full PDF" link after the abstract.)

Have you seen the journal Asian Myrmecology? Currently the articles are offered for free online at the website.