Category: Ants and Plants

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Ants of Tucson, Arizona: Crematogaster opuntiae

There is a story on the Internet of a myrmecologist (unfortunately unnamed) finding 10 species of ants, including army ants, while waiting for a flight at the Tucson, Arizona airport. I had two hours in Tucson on Saturday morning, so I wondered if I could do as well. For the next few days we’ll see if I was up for the challenge.

The first ant I found was a worker of the genus Crematogaster, named for its lovely heart-shaped rear section or gaster. This cutie is Crematogaster opuntiae, a specialist often found feeding on the extrafloral nectaries of cacti. This particular cactus is a cholla, Cylindropuntia.

Although Crematogaster opuntiae workers are known for chasing herbivores away from cacti in defense of the extrafloral nectaries, they are also predators of other insects, such as termites.

For more information, try:

Charles H. Pickett and W. Dennis Clark. (1979).The Function of Extrafloral Nectaries in Opuntia acanthocarpa (Cactaceae) American Journal of Botany. 66(6):618-625.

Discover Life has a photograph of Crematogaster opuntiae raiding termites

Alex Wild also has some fabulous photographs

Finally, if your French is good, Fourmis et Cactus à Nectars Extra-Floraux


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Cactus Bud Ants

You wouldn’t think there would be much to attract ants to a cactus. They have waxy stems covered with spines.

There is one structure in this photograph, however, that is highly attractive to ants.

Do you see it yet? No, it isn’t the clusters of extrafloral nectaries.

It’s a bud.

What are the ants doing?

In case you aren’t familiar with the relationship between ants and cacti, the ants are visiting to obtain a sugary liquid produced by the plant. It would appear that the softer, quickly growing tissue of a bud is more susceptible to being eaten by plant-feeding caterpillars or beetles. It is likely the ants will defend their free “soda fountain” and chase these sorts of pests away.

Those of you who have seen extrafloral nectaries on cacti, do you agree that those yellow bulges between the spines above the bud are extrafloral nectaries?

Here’s an ant visiting an extrafloral nectary on a barrel cactus.

Any ideas why the two separate structures?

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Myrmecodia tuberosa – An Ant Plant

Last month when we visited the Denver Botanical Garden, I had to get a photograph of this lovely specimen.

That was because it was identified by a sign as Myrmecodia tuberosa, a commonly known “ant plant.”

What is an ant plant?

Certain types of plants, like this one, have special chambers or cavities within the walls of their swollen stems. The chambers are called domatia from the Latin word domus (house). The plants are called myrmecophytes or ant plants because ant colonies commonly take up residence in the domatia.

Why would plants provide living quarters for ants? In exchange for a place to live, the ants provide protection from herbivores and cleaning services to remove plant parasites and fungi. The ants may also pick up and disperse the plants’ seeds in some cases.

Often plants associated with ants are epiphytes, which means plants that are normally found growing on other plants or structures rather than in the soil. In these cases, the ants may provide essential nutrients in addition to their protection services. The ants store their trash in special areas within the domatia where it becomes composted and the plants absorb the nutrients from it. Scientists have actually given the ants food labeled with radioactive compounds and found the radioactivity ended up in the plants shortly after.

Ants can provide other services to plants, as well. In the tropical rain forests, certain species of ants take the seeds of unusual plants and purposefully plant them on their nests. The plants grow to cover the ant nest, protecting it. The ant garden plants, as they are called, supply nectar to the ants through extrafloral nectaries. The ants supply nutrients and protection to the plants. The plants the ants choose do not grow anywhere else, but only on ant nests.

This particular specimen did not appear to house ants. Maybe I should offer the curators some help with that. 🙂

Have you ever seen an ant plant full of ants? Do you know what kind?

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Ants and Spurge Part 2: Nectar and Pollination

Have you ever heard a gardener comment, “Spurge plants always have ants,” and wondered if it was true? I admit searching ground spurge (Chamaesyce prostrata) for ants when I find the weeds, and I am often rewarded. Ants are attracted to spurge seeds (previous post), but is there more to the story?

Let’s take a look at a spurge with numerous ants milling around it. Most are Forelius.

The ants seem to be visiting the complex structures that pass for flowers in ground spurge.

In this photograph the ant on the right appears to be visiting the flower. But there is also an aphid on the same plant.

Yes, there are aphids on the plant.

The ants are also collecting honeydew from the aphids.

This leads to the question, how significant are the two sources of sweets? Ants are known to regularly visit the nectaries of the invasive weed, leafy spurge, but I wasn’t able to find out much about ground spurge.

Another question arises about whether ants might be capable of pollinating ground spurge. Ants are thought to pollinate certain low-growing plants with small flowers that are tight to the stem, and ground spurge certainly fits the bill.

Selleck, et al. 1962 reported that leafy spurge was pollinated by ants. After reading their evidence, however, it might be a shaky conclusion.

What is up with ants and spurge? Do ants visit spurge where you live? Do the ants gather nectar? Any evidence of pollination?

Reference:

Selleck, G.W.; Coupland, R.T.; Frankton, C.(1962). Leafy spurge in Saskatchewan. Ecological Monographs. 32:1-29. free .pdf.