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
- 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
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.