Ants and Plants

Looking for ants? Sometimes it is only a matter of finding the right plant.

Most people know ants come to the extrafloral nectaries on peony buds and we've talked about sandmat before, but are there any other plants that regularly attract ants?

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The umbel flowers of wild parsnip (Pastinaca sativa) might be a good place to look for different kinds of ants.

wild parsnip leaf

Wild parsnip grows in wet areas, such as along creeks or streams.  It can also be found growing on roadsides. At four to five feet tall, the flowers are right at eye level for many people. Be careful when visiting the plant, however, because contact with the sap can cause burns to the skin when exposed to sunlight.

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Ants, flies, wasps and other insects can be readily found visiting the large nectaries of open flowers.

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Although these particular ants were fairly small, large ants such as Formica and Camponotus were also seen on wild parsnip flowers.

What are the ants doing on the plants besides collecting nectar? Wild parsnips are considered to be invasive weeds in many areas. Therefore, ants feeding on nectar might considered to be favorable if they interfere with the plants' success or might be unfavorable if the ants protect the plants from herbivores. Jing Yang and Dana Dudle from the Biology Department at DePauw University studied the effects of ants on the reproductive success of wild parsnip by excluding flying versus crawling insects from certain flowers. In their limited investigation they found no differences in plant fitness whether ants were present or not, but suggested further studies needed to be done.

Regardless, if you are interested in watching ants you should keep your eye out for wild parsnip flowers.

Ave you ever seen ants on wild parsnip?

When you are searching for ants, what plants do you look for?

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What do you think is going on here?

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These are Forelius ants visiting the flower buds of a common landscape tree in the Southwest, the desert willow, Chilopsis linearis.

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Desert willows are not really willows at all, but belong the plant family Bignoniaceae, making them relatives of catalpa trees.

The trees have large, tubular flowers that attract hummingbirds and bees. Some varieties have dark magenta flowers,

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whereas others have delicate, light pink flowers.

Forelius

Forelius are heat-loving desert ants. Many of the Forelius in this area are Forelius mcccooki (key to US species). They nest in the ground, but commonly forage on plants where they are known to gather sweet fluids from nectaries.

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Which leads us back to the question:  what are these Forelius workers doing on the desert willow flower buds?

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Both catalpa and desert willow are known to have extrafloral nectaries on the leaves. (Rico-Gray and Oliveira in 2007 defined extrafloral nectaries as sugar-producing glands found on the leaves, stems or stipules of plants.)

extra-floral-nectaries-desert-willow_0160Here are some buds from a desert willow tree that lacked ants. See the green spots?

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Do you think the light green structures (circled) are possibly what Rico-Gray and Oliveira define as circumfloral nectaries, that is nectaries around flower structures that are not attracting pollinators?

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Interestingly, a number of the flower buds on the tree without ants showed damage. What do you think caused this damage?

Looking into the literature, Ness (2003) found Forelius pruinosus workers attacked Ceratomia catalpae caterpillars on catalpa trees after visiting extrafloral nectaries. Ness also showed that leaf damage increased the sugar flow of nectaries within 36 hours. This supports the classic idea that plants attract ants to help fend off herbivores.

On desert willow, however, things might be even more complicated. Carey, Visscher, and Heraty (2012) found that an Eucharitid parasitoid of ants, Orasema simulatrix, laid its eggs in the extrafloral nectaries of desert willows, where the planidia had access to big-headed ant workers feeding there. The article has some fabulous photographs of extrafloral nectaries, by the way.

So, do you think the Forelius were visiting circumfloral nectaries? Have you seen any other ants visiting similar plants?

What do you think of Rico-Gray and Oliveira's separation of exrafloral nectaries from circumfloral nectaries? Is there a clear need to make a distinction? Would circumfloral nectaries have more likelihood to contribute to successful seed production than extrafloral nectaries?

References:

Carey B., K. Visscher, and J. Heraty. (2012) Nectary use for gaining access to an ant host by the parasitoid Orasema simulatrix (Hymenoptera, Eucharitidae). Journal of Hymenoptera Research. 27: 47-65. (Retrieved online)

Ness, J. H. (2003) Contrasting exotic Solenopsis invicta and native Forelius pruinosus ants as mutualists with Catalpa bignonioides, a native plant. Ecological Entomology. 28 (2): 247–251. (Retrieved online as .pdf)

The Ecology and Evolution of Ant-Plant Interactions (Interspecific Interactions) by Victor Rico-Gray and Paulo S. Oliveira, particularly pages 115 - 123.

Paperback: 320 pages
Publisher: University Of Chicago Press; 1 edition (July 15, 2007)
ISBN-10: 0226713482
ISBN-13: 978-0226713489

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The incredible relationships between ants and pitcher plants have been in the news lately, so it might be time to summarize some of the most recent discoveries.

 

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Ant drinking nectar from the peristome of an upper pitcher of Nepenthes rafflesiana. Bako National Park, Sarawak, Borneo. Photograph from Wikimedia.

 Pitcher Plants - An Introduction

Pitcher plants are part of a group of carnivorous plants that are known to capture arthropods, particularly insects. There are many different species, and some are not all that closely related.

 

 

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The pitcher plants are named for their bottle-shaped structures that hold fluids. Insects and other arthropods roaming nearby often slide into the fluid and drown, not because they are particularly clumsy, but because the inside upper rim is very slippery. The slipperiness may be due to waxes or due to special hairs (trichomes), as with the example below.

 

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Some pitchers serve simply as passive traps that capture anything wandering by, whereas others produce nectar at the lip (called the peristome) to attract even more prey.

Ants and Pitcher Plants

Unlike most other arthropods, ants have some special relationships with pitcher plants. Many of these relationships are not well understood yet.

In this video we can see the ants can run around on this particular pitcher plant without falling in, although a sawfly has already been captured. A related video (link comes up onscreen towards the end of this video) shows a woodlouse falling right into the same trap. The ants do not appear to be feeding on nectar in this case.

 


 

Dr Ulrike Bauer from the University of Bristol, UK and her colleagues have been studying how insects are captured by certain pitcher plants which supply nectar. They found that when the traps of these pitcher plants are dry, ants can walk on them easily. When the traps are wet, then the ants fall in and drown.

 

 

Bauer and her colleagues have recently taken their work a step further further and suggest that pitcher plants may benefit from being alternately wet and dry. More ants are recruited to pitcher plant nectar when the pitchers are dry. When the traps become wet again, the ants fall into the traps in greater numbers than if the pitchers had been constantly wet (2015).

Probably the most intriguing discovery has been the relationship between Camponotus schmitzi carpenter ants and the fanged pitcher plant, Nepenthes bicalcarata (object of the famous photograph by Mark Moffett).

These tiny carpenter ants nest in the tendrils of the pitcher plant. Remarkably the carpenter ants are able to swim through the fluid in the pitcher plant that drowns other insects. In fact, the worker ants swim around in the pitcher to remove insects as food for themselves and also catch pupae of a species of fly that lives in the pitcher plant fluids.

Some early workers thought the ants might be ripping off the plants by taking their food, but later work has shown the carpenter ants provide a number of services to the pitcher plant.

The ants:

  1. Clean the rim of the peristome, making the pitcher a better trap.
  2. Chase away some herbivores that might attack the pitcher plant
  3. Capture fly pupae, which helps keep valuable nutrients available to the plant.
  4. Knock arthropods into the trap when they are protecting the pitcher.
  5. Remove large carcasses that might rot/putrify the pitcher.

All of these services mean that Nepenthes bicalcarata pitchers are long lived and so not need to be replaced as frequently.

This video shows Camponotus schmitzi carpenter ants in action. It is based on the work of Thornham et al. from their 2012 paper  in Functional Ecology.


 

Amazing!

Have you ever seen ants around or in pitcher plants? Do you know what kind?

References:

Bauer, U., M. Scharmann, J. Skepper, W. Federle. 2012. 'Insect aquaplaning' on a superhydrophilic hairy surface: how Heliamphora nutans Benth. pitcher plants capture prey. Proceedings of the Royal Society B: Biological Sciences, 280 (1753): 20122569 DOI: 10.1098/rspb.2012.2569 (free .pdf available)

Bauer U, Federle W, Seidel H, Grafe TU, Ioannou CC. 2015 How to catch more prey with less effective traps: explaining the evolution of temporarily inactive traps in carnivorous pitcher plants. Proc. R. Soc. B 282: 20142675.
Downloaded from http://rspb.royalsocietypublishing.org/ on January 15, 2015

Scharmann, M., D.G. Thornham, T.U. Grafe & W. Federle 2013. A novel type of nutritional ant-plant interaction: Ant partners of carnivorous pitcher plants prevent nutrient export by dipteran pitcher infauna. Plos One 8(5) e63556. (Article available)

Thornham, D.G., J.M. Smith, T.U. Grafe & W. Federle 2012. Setting the trap: cleaning behaviour of Camponotus schmitzi ants increases long-term capture efficiency of their pitcher plant host, Nepenthes bicalcarata. Functional Ecology 26:11-19. (Article available)

2 Comments

Last week I flipped over a rock about six inches square and found this:

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Okay, it doesn't look like much until you zoom in closer.

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The grayish-mound is a solid mat of oval, wrinkly seeds. Apparently they had been gathered and stored by the Southern fire ants (Solenopsis xyloni) you see running around. The ants were in full defensive mode.

The seeds were both on the ground and on the underside of the rock, so there was quite a mass of them.

 

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Seeing the seeds reminded me of an earlier time (above photograph) I had found a similar cache of seeds under a rock . At the time I didn't know what plant they were from, but now I have figured it out.

These seeds are from a type of ground spurge, Chamaesyce prostrata. Another common name is sandmat. (See post about Southern fire ants and sandmat).

The University of Arizona has an illustration of the plant in their older weed manual under the name Groundfig Spurge, Euphorbia prostrata. See the seed labeled "d" in the illustration?

A quick search of the internet revealed the UC IPM website states "Weed seeds, particularly spurge, may attract the ants away from the bait..." This statement is referring to Southern fire ants in almond groves.

Seems like there might be something worth investigating going on here.

Have you ever seen Southern fire ants with seed caches? What kinds of seeds did you find in them?