Month: June 2010

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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.

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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.

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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?

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Question 1. Ant Digestion

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.

Question 1)      I’m interested in the ant’s digestion process and its role in the colony. I’ve read that some ants, the fully mature ones that is, can’t digest solid food due to their narrow waists. So is it true that the ants would take the solid food back to the colony and give them to their larvae where, there, it is digested and converted into a liquid form? I’m guessing that the larvae have the enzymes to digest the solid food. But does this process apply to ALL ants in terms of species?

I actually tackled this topic to some extent in my post about ant larvae, but I’ll re-state some of the high points here.

Because the petiole is so narrow and constricted, ants do have a specialized digestive system. When an ant eats, the food goes into a special pouch called the infrabuccal pocket in its mouth, which acts like a food strainer. The infrabuccal pocket prevents large particles from continuing into the digestive system. Probably the size of the particle allowed through varies from species to species, but in the carpenter ant, Camponotus pennsylvanicus, particles larger than 100 microns are excluded from entering the alimentary canal . The liquid and tiniest particles that can move through the narrow petiole are sucked into a tube and pass through into a special reservoir in the gaster called the crop. The ant spits out the leftover bits that were too big to go through the food strainer. The rejected bits are called infrabuccal pellets.

Scientists have long known that the worker ants feed all solids to the larvae first for processing. The larvae were thought to chew up, swallow and predigest the food, using enzymes, as you guessed. The larvae then regurgitate it back to the workers to distribute throughout the colony.

Recently, however, researchers have shown that in one species of bigheaded ants (Pheidole) the workers actually place the food on the surface of the belly of the larvae in a special groove (larvae lay on their backs). The larvae spit out the enzymes onto the food, basically drooling on themselves. After a few hours, the workers come back and pick up the slime that results, feeding some of it to the larvae and taking some for themselves. According to videos of the larvae processing bits of fruit fly, the larvae very rarely sip any of the gooey liquid while the food is dissolving; they wait patiently until the food is done and let the worker ants feed them.

Probably the most surprising aspect of ant larvae is that not only do worker ants bring them food, but the larvae are often sources of food themselves. Certain species of ant larvae have special structures that allow the workers to access the internal body fluids (hemolymph), a sort of pump or “tap.”

The so-called Dracula ants take things a step further. These rare ants get their name from the fact that they cut holes in the sides of the larvae and suck out hemolymph. Although this sounds pretty gruesome, the larvae survive having holes bitten into them and later become workers themselves.

Another odd behavior of this group is that the workers carry the larvae to their food and place them on it, rather than carrying the food to the larvae, as most other ants do. For example, instead of cutting up a caterpillar or millepede into chunks and carrying it into the nest to feed the larvae, Dracula ants carry the larvae out to the caterpillar. Once they have fed, the larvae become food themselves.

If you think about it, the adult ant’s weird digestion system does work because adults don’t need a lot of protein for growth, they mainly need carbohydrates for energy. The same is true for some birds. The adult birds may drink sap or nectar, but feed protein-rich insects to their growing chicks.

Anyone else have anything to add?

References:

Gotwald, W.H, Jr. 1969. Comparative morphological studies of the ants, with particular reference to the mouthparts (Hymenoptera:  Formicidae). Cornell University Agricultural Experiment Station. Memoir 408.

Hansen, L. D., and J. H. Klotz. (2005). Carpenter ants of the United States and Canada. Ithaca, NY: Comstock Publishing Associates. This book has an excellent chapter on ant morphology.

Keiichi Masuko (1986). Larval Hemolymph Feeding: A Nondestructive Parental Cannibalism in the Primitive Ant Amblyopone silvestrii Wheeler (Hymenoptera: Formicidae). Behavioral Ecology and Sociobiology, Vol. 19, No. 4: 249-255

Keiichi Masuko (1989). Larval Hemolymph Feeding in the Ant Leptanilla japonica by Use of a Specialized Duct Organ, the “Larval Hemolymph Tap” (Hymenoptera: Formicidae). Behavioral Ecology and Sociobiology, Vol. 24, No. 2: 127-132

Keiichi Masuko (2008). Larval stenocephaly related to specialized feeding in the ant genera Amblyopone, Leptanilla and Myrmecina (Hymenoptera: Formicidae). Arthropod Structure & Development Volume 37, Issue 2: 109-117

D. L. Cassill, J. Butler, S. B. Vinson and D. E. Wheeler (2005). Cooperation during prey digestion between workers and larvae in the ant, Pheidole spadonia. Insectes Sociaux Volume 52, Number 4: 339-343.

Nectar and honeydew are good choices of food for adult ants.
Nectar and honeydew are good choices of food for adult ants.