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If you have a pool, you know that most insects don't have a chance if they fall into the water. Here at Wild About Ants, however, we know ants often do the seemingly impossible. To prove it, let's look at the ability of certain species of ants to swim.

Camponotus-pennsylvanicus-very-cool

In a recent article in Myrmecological News, Gora et. al. reported on their investigation into swimming by the carpenter ant, Camponotus pennsylvanicus. They found carpenter ants use vision to find escape platforms from the water. One hundred percent of the control ants placed in the water of the test apparatus were able to swim to the edge and get out of the water successfully. Ants with their vision occluded, on the other hand, failed to exit the water.

Although this study focused on ants swimming as a method to escape from water if they fall in accidentally, some Camponotus ants in pitcher plants are able to actively swim to capture mosquito pupae for food. In this video you can see how they move all six of their relatively short legs to push through the liquid.

As you might expect, ants that live in areas that are regularly flooded by tides, such as ants living in mangrove swamps, are particularly good at swimming.

This video from Life in the Undergrowth shows mangrove ants running across shallow water and then at about 1:02 minutes actively swimming in the water. Notice how the swimming ant holds its hind legs out behind it like a rudder.

Yanoviak and Frederick tested 35 species of tropical forest ants to see how many had the ability to move through water in a directed way. Of those, ten species were able to show rapid directed movements and ten more exhibited slower, but directed movements. The remaining species apparently needed tiny life jackets.

The bottom line is that although different species of ants vary in their ability to swim, some are quite adept at it.

Previous Posts at Wild About Ants:

References:

Gora, E.M., Gripshover, N. & Yanoviak, S.P. (2016) Orientation at the water surface by the carpenter ant Camponotus pennsylvanicus (De Geer, 1773) (Hymenoptera: Formicidae)  Myrmecol. News 23: 33-39. (Let me know if the link doesn't work and I'll find it for you.)

S. P. Yanoviak, D. N. Frederick (2014) Water surface locomotion in tropical canopy ants. Journal of Experimental Biology 217: 2163-2170; doi: 10.1242/jeb.101600

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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)