Tag: The Consult-ant

Posted on

Memory in Ants

Mike wrote to the “Consult-Ant” with a number of questions about ants. I am going to try to answer each one in a separate post. For the original list of questions and links to all answers, visit here.

6) So ants have pheromones they lay to provide trails to sources of food, but I’ve read somewhere that ants have memory. Can you explain more about that? A ‘leader’ ant would teach a ‘follower’ ant towards a food source. Is that true? with only certain species?

Although their brains are obviously very different from ours, we do have some evidence that worker ants do have memories. For example, James Hare and Thomas Eisner showed that workers ants that had been exposed to moth eggs (Utetheisa ornatrix) full of nasty alkaloids would still avoid moth eggs days later. But not just avoid toxic eggs. In an elegant study, Hare and Eisner were able to rear moths that did not contain the alkaloids, producing eggs that were perfectly edible. Ants with no previous exposure to the alkaloid-laden eggs would eat the alkaloid-free ones readily. It was the workers with previous experience (up to 33 days prior!) that would avoid both kinds of moth eggs.

In a paper in Myrmecological News, Dornhous and Franks give an overview of cognition in ants, and other insects. They report that foraging ants use memory to find food sources, and can even remember times of day the food sources are available. Ants can also remember where they have looked for new nests. Wood ants apparently memorize visual “snapshots” of landmarks as they travel about. Although chemical cues are important, if an ant is dropped into its environment in a place with no chemical trails, it might be able to orient back to the nest using visual cues. Ants have been known to be able to learn to move through mazes since Schneirla’s work in the early 1940’s, so are able to improve their performance of certain tasks.

Ant running a maze.

Dornhous and Franks point out that most of the studies of cognition in insects have been carried out with honey bees and fruit flies, for various reasons. There is still a lot of work to be done on ants.

As for the leader and follower ants, would you believe that ants could be teachers? When researchers looked at how ants lead their nest mates to new sources of food or a better nest, they found that the experienced ants actually taught the others where to find the target during a process known as “tandem-running.” Tandem running is when one ant follows another closely while running.

To discover whether or not the ants were actually teaching each other, first the investigators needed a solid definition of what it means to be a teacher. They decided that to be a true teacher, the ant must change its behavior when it encounters an inexperienced ant. At a cost to its own ability to perform the task, it must set an example so that the untrained ant can learn more quickly than it could have without training.

Sure enough, teacher ants approached uninformed nest mates and literally showed them the way to the food or new nest by running ahead. The follower gives feedback to the leader by continuous touching with her antennae. By teaching others the path to take, the teacher ant ran slower than it would have without a follower, but the pupil ant found the target in two-thirds the time it would have taken without help.

To learn more:

Dornhous, A. and N. R. Franks. (2008). Individual and collective cognition in ants and other insects (Hymenoptera:  Formicidae). Myrmecological News. 11:  215-226.

Franks, N.R. and T. Richardson. (2006). Teaching in tandem-running ants. Nature. 439:  153.

Hare, J.F. and T. Eisner. (1993). Pyrrolizidine alkaloid deters ant predators of Utetheisia ornatrix eggs: effects of the alkaloid concentation, oxidation state, and prior exposure of ants to alkaloid-laden prey. Oecologia. 96: 9-18.

R. Josens, C. Eschbach, and M. Giurfa. (2009). Differential conditioning and long-term olfactory memory in individual Camponotus fellah ants. J. Exp. Biol. 212:1904-1911 Retrieved from http://jeb.biologists.org/cgi/content/abstract/212/12/1904

Nowbahari, E. (2007). Learning of colonial odor in the ant Cataglyphis niger (Hymenoptera; Formicidae). Learning & Behavior, 35: 87-94. Retrieved from http://lb.psychonomic-journals.org/content/35/2/87.abstract ( free .pdf available)

Y. Provecho and R. Josens. (2009).Olfactory memory established during trophallaxis affects food search behaviour in ants. Journal of Experimental Biology. 212: 3221-3227. Retrieved from http://jeb.biologists.org/cgi/content/abstract/212/20/3221 (.pdf available)

Schneirla, T.C. (1943). The nature of ant learning II. The intermediate stage of segmental maze adjustment. Journal of Comparative Psychology. 35:  149-176.

What is she thinking?
What is she thinking?
Posted on

Questions About Ant Pheromones

Mike wrote to the “Consult-Ant” with a number of questions about ants. I am going to try to answer each one in a separate post. For the original list of questions and links to all answers, visit here.

4)      Besides making trails and setting alarms, are there any other kinds of unique pheromones? Such as, attracting the queen ant or inducing certain behaviors like digging.

Sure, there are a lot of different pheromones in ants. Ants use pheromones to

  • recruit to food sources,
  • mark the way to new nest sites during emigration
  • aggregate
  • mark territories
  • recognize nestmates
  • “call”- the release of pheromones by reproductive females to attract males
  • induce nestmates to defend the nest (alarm)

to name a few. Some queens release pheromones that induce workers to kill larval forms that would become reproductives, or that prevent virgin queens from shedding their wings. In carpenter ants, the males release a pheromone from their mandibular glands that signals to the female reproductives that it is time to fly from the nest and join the mating swarm. (Holldobler and Maschwitz 1965, as cited in LD Hansen and JH Klotz, Carpenter Ants of The United States and Canada).

Behaviors like digging can also be stimulated by non-chemical signals, such as stridulation (making sounds) by buried worker ants trying to get nestmates to dig them out.

Knowledge of ant pheromones a bit rusty?  Let me explain what we are talking about. Ants produce chemicals, in fact they are walking chemical factories. Bert Holldobler and E.O. Wilson wrote extensively about how ants use chemicals for communication in Chapter 7 of their book, The Ants (starting on page 227).

The term “pheromone” is defined as a substance released by an organism to the outside that causes a specific behavioral or physiological reaction in a receiving organism of the same species. [Nordlund, D. A. and W. J. Lewis. (1976). Terminology of chemical releasing stimuli in intraspecific and interspecific interactions. J. Chem. Ecol. 2: 211-220.]

For example, this video shows an ant laying trail pheromones. Other ants will detect the chemical in the trail and follow it back to the food.


All of these chemicals are made in exocrine glands found throughout the ant’s body.

In the head are the

  • mandibular gland – often produces alarm and defense compounds, extends all the way to the gaster in certain Camponotus
  • maxillary gland -source of digestive enzymes
  • propharyngeal gland – source of digestive enzymes
  • postpharyngeal gland – source of cuticular hydrocarbons (colony odor) and also food for larvae
  • antennal glands – found in Solenopsis fire ants

In the alitrunk are the

  • labial gland – equated with a salivary gland
  • metapleural gland (labeled in illustration) – source of antibiotic compounds, occasionally alarm pheromones/repellents

    • (Archetype has an awesome post about the structure and function of the metapleural gland.)

In the gaster, we find the

  • poison gland – source of defensive formic acid in Formicinae, recruitment to food in some myrmecines
  • rectal gland
  • sternal gland (Pavan’s gland) – trail pheromones
  • Dufour’s gland – often the source of trail pheromones
  • pygidial gland
  • etc.

ant-glands

The presence or absence of these glands, their structure and their contents varies between ant species, and even within individual caste members of a given species. The pheromones used and the message they contain are species specific by definition. That means what scientists learn about the pheromones of one species may not have general application to any other species, although some have been found to overlap.

To learn more about the chemistry of ant pheromones, try The Pherobase, a website of known pheromones, attractants, etc. You can search the database by animal taxon, or go directly to the Formicidae page.

There you can find out, for example, that the trail pheromone for Atta texana is me-4me-pyrrole-2-carboxylate, and what it’s structure looks like. Or the mandibular gland components of the exploding carpenter ants of Camponotis cylindricus group. Solenopsis invicta queens apparently produce (E)-6-(1-Pentenyl)-2-pyranone for recognition, that is so that the workers know she is their queen. This site is really cool if you are an ant geek.

5)      The ant uses their antennae to pick up ant pheromones, so if that’s the case, then do ants necessarily ‘smell’ food if the pheromone is blown towards the ant’s way? Essentially speaking, can ants smell their way to food?

Oh, definitely yes. In a recent post I discussed how certain ants can even use odors as a type of chemical map to find their way around. Their way of orienting can be called a “topochemical” map. Of course ants may use a variety of cues to find food, including sight, but it makes sense that they can detect plant chemicals and even those of sources of honeydew like aphids and scales.

If anyone has posts or references that might be helpful to Mike, please let us know.

Posted on

Question 3 Ant Queens and Pheromones

Mike wrote to the “Consult-Ant” with a number of questions about ants. I am going to try to answer each one in a separate post. For the original list of questions and links to all answers, visit here.

3)      I’ve been meaning to catch an ant queen, but I’ve been curious about other methods of catching one. Are there ant pheromones that can basically attract queen ants to come out of the colony? I assume that each ant species would probably have their own type of pheromones, so I’ll have to find out which species I’m planning to catch, which leads me to the next question: Where can I get these pheromones? Can I synthetically make them on my own? What differentiates certain pheromones from another? Subtleties in molecular structure?

That’s an interesting idea, Mike, but it actually works in reverse. The queen produces pheromones to attract males during the mating flight (although some species have other signals, like harvester ant queens stridulate). Once she has started a colony, usually the pheromones she produces regulate the behavior of the workers, attracting them to her. She is the most important member of the colony after all. I guess it is possible that wafting an alarm pheromone into a nest might drive out the queen, but your chances of finding her amidst the other ants? I’m not sure.

Chemists have definitely synthesized pheromones for insects, usually for those with economic importance, for example gypsy moths. The chemistry is often quite complex. The chemical structure may vary by something as simple as chirality or as complex as being a totally different molecule.

If you want to catch a queen, nothing beats learning all you can about the life history of the species you are interested in and then going out when at the time of year when swarms occur (often depends on the weather) and look for mated queens. I find queens all the time because I’m looking for ants, and queens start their colonies where other ants are successful.

show-queen

Anyone else out there have any ideas for Mike?

Edit: In researching your next question I did find evidence that in carpenter ants, the males release a pheromone from their mandibular glands that signals to the female reproductives that it is time to fly from the nest and join the mating swarm. (Holldobler and Maschwitz 1965, as cited in LD Hansen and JH Klotz, Carpenter Ants of The United States and Canada). Although they would be unmated, that might be a way to entice them from the nest. The other problem I foresee is that the unmated queens would need to be physiologically ready to go on their mating flight or the pheromone wouldn’t work.

See the next post for more information on pheromones.

Posted on

Question 2 Ant Undertakers

Mike wrote to the “Consult-Ant” with a number of questions about ants. I am going to try to answer each one in a separate post. For the original list of questions and links to all answers, visit here.

2)      I’ve noticed that ants carry pick up their dead and move them. I’ve learned that they do this to basically ‘take out the trash’ for sanitary purposes. But I’ve also noticed that these ants also carry their dead when they’re far away from any ant hole. So, referring to my other question, if it’s true that ants do take the solid food back to their larvae, then are these ants carrying their dead back to their larvae for consumption? Assuming ants are cannibalistic, which I’m not sure of.

Recently I photographed some clues that might shed some light on your ant carrying mystery.

carrying-ant

This Forelius worker is carrying another ant.

carrying-ant2

She carried it right back to the nest and dragged it in. Notice, however, the dead ant has two “nodes.” It is a worker of Solenopsis xyloni from a nearby colony. The area around the Forelius nest was strewn with Solenopsis parts.

Many ants will carry fallen foes back to the nest as food, as well as the enemy colony’s pupae, larvae and eggs. In that way, ants are indeed cannibalistic.

It makes sense to process and eat healthy enemy ants. It does not, however, make sense to eat dead ants from the home colony because they may be diseased or have parasites.  Worker ants do carry their dead nestmates to the refuse heap, as shown by the famous ant scientist, EO Wilson in the 1950’s. Wilson figured out that chemicals were involved in the recognition of dead ants, particularly oleic acid. When he dipped oleic acid on a healthy, living ant, her sisters still dragged her off the the ant graveyard. The ants was not allowed back into the colony until she managed to clean herself up.

For the EO Wilson story, visit ‘Hey I’m Dead!’ The Story Of The Very Lively Ant by Robert Krulwich

Finally, worker ants sometimes carry live ants as well.

Comments?