When we are not doing experiments, my son and I have been reading Animal Architects: Building and the Evolution of Intelligence by James R. Gould and Carol Grant Gould.
We have enjoyed the book so far. It is not an easy read, but the stories of the different animals are fascinating. The book is much more than a review of animal construction techniques, it is how different behaviors reflect an animal’s cognitive abilities. It also reveals how researchers interested in cognition measure an animal’s potential.
The only point that has disappointed us has been the relatively thin coverage of ant architecture. Aside from a brief overview of the nests of army and weaver ants, the Goulds pretty much skip the ants, giving the excuse that what ants do is mostly underground and hard to study.
If you are interested in animal architecture, there are ant nests that do deserve attention. Take a look, for example, at this leafcutter ant nest. It definitely rivals that of the fungus-growing termites in its complexity and size.
Another excellent example of elaborate engineering by ants is found in Holldobler and Wilson’s Superorganism book on pages 338-339. Harpegnathus saltator ants build a nest that comes complete with “wallpaper,” and is thought to withstand flooding that occurs during the monsoon season.
Ants are also capable of making decisions about potential new nests sites, a similar issue that faces honey bees when swarming. The nest emigrations of tiny acorn ants of the genus Temnothorax have been studied extensively. Evidence suggests that scout ants investigating potential new nest sites actually have a way to “measure” the interior of a cavity to determine if it is suitable.
Here’s an example experimental set up:
And finally, check out Alex Wild’s wonderful photographs of examples of ant architecture.
What do you think? Are ants capable of intricate architecture?
For those of you who didn’t get to see Mark Moffett’s presentation last evening at the Mesa Arts Center, here is an interview from our local radio station KJZZ. (There’s a gray square button in the upper left hand corner of the box below that turns off the audio.)
Dr. Moffett has a book coming out soon. Given his abilities as a photographer, I can’t wait to see it.
We have been inspired by books lately. In the last post, our inspiration was an adult-level book about katydids. Today it is the children’s picture book Little Black Ant on Park Street by Janet Halfmann and Illustrated by Kathleen Rietz. The book is the next installment in the excellent Smithsonian’s Backyard series. I reviewed the book at my Wrapped in Foil blog and putting up related hands on activities for children on my Growing With Science blog, but here I’d like to take a look at the biology of the species.
The little black ant, Monomorium minimum, is a relatively tiny species, native to North America.
The workers are black, uniform in size and only about 1/16th of an inch long (1.5 mm). The petiole has two segments.
Monomorium minimum belongs to the tribe Solenopsdini. The workers have antennae with a three-segmented club. Their fire ant relatives have a two-segmented club.
Unlike the stereotypical ant colonies with only one queen, colonies of little black ants often contain multiple queens.
Monomorium minimum workers feed on honeydew, and scavenge dead insects and other arthropods, usually during the warmest part of the day. When foragers find a suitable item, they recruit nest mates by releasing a pheromone. Once recruited, groups of workers cut up larger items or cart away smaller ones.
As described in the book, when workers of M. minimum run into other ant species that scavenge dead arthropods, the minimum workers raise their gasters, vibrate and release poison gland secretions to chase away any rival ants. This behavior is called “gaster flagging.”
Here’s a short video of gaster flagging in another species.
For a little ant, they pack a big punch. Monomorium minimum colonies can invade imported fire ant, Solenopsis invicta, colonies and take over.
Given that these little ants are so interesting and relatively widespread and common, I’m surprised how little information I was able to find on them. Perhaps this new children’s book will spark some scientific inquiry by the next generation of myrmecologists.
Eldridge S. Adams and James F. A. Traniello. 1981. Chemical interference competition by Monomorium minimum (Hymenoptera: Formicidae). Oecologia. Volume 51, Number 2 / January, 1981. pdf available
I’ve just been reading a book on katydids, which are insects renowned for their ability to sing. What about ants? Are they the strong silent types?
It turns out that ants can make plenty of music. They can squeak, drum and rattle as well. There is nothing quiet about ants. As Dr. Francesca Barbero of the University of Turin says, “Sound in information exchange within ant colonies has been greatly underestimated.”
Stridulation
Detail of the pars stridens (in yellow) on the forth abdominal tergite in a Pachycondyla villosa worker (Scanning Electron Micrograph, Roberto Keller/AMNH)
Ants with underground nests occasionally get buried when a tunnel collapses. Scientists have shown trapped ants of certain species can make sounds by rubbing sections of their rear section or gaster together. On one segment of the gaster there is a patch of tiny ridges like a file. On the petiole is a curved ridge called a scraper. The ant produces a squeaking sound when she rubs them together, which known as stridulation. You can produce a sound in a similar way by rubbing a craft stick across a comb. When other workers detect the sound, they rush to help dig out the trapped ant(s).
Researchers have been able to record sounds from individual ants. The sounds are in the audible range for humans and can be heard distinctly when amplified. Listen to the sounds of a fire ant stridulating at Stridulation Sounds of Black Fire Ants by Dr. Robert Hickling. (The link is broken, so I found some more recordings -later post).
Stridulation has other functions as well. Male and female harvester ants sing to one another as they take off on their mating flights. Mated females also stridulate to signal to pursuing males that they are no longer interested. In other species, foragers may stridulate when they find food to attract help, although they often release pheromones as well.
Leafcutter ants are known to stridulate while cutting pieces of leaf. It appears the noise the cutting ants make attracts other ants to come take the pieces of leaf to carry them back to the nest. Some ant scientists have suggested that the vibrations improve the ants’ ability to cut smoothly through the leaf. Leafcutter ants also produce sounds while building their nests in the soil.
Example video of Acromyrmex ant stridulating
Some other insect species associated with ants also stridulate to attract the ants’ attention. The caterpillars of the beautiful Imperial blue butterfly have “teeth” on their abdomen, which they scrape against a series of grooves to produce grunts and hisses. They can also make a drumming sound. All these different calls seem to be used for different situations, but not all the details are clear yet. What is known is when scientists glued up the noise-producing organs with shellac, the ants took longer to find the caterpillars and spent less time with them than with the ones who had not been silenced.
As I mentioned in the post about blue butterflies, Rebel’s large blue (Maculinea rebeli) larvae have recently been shown to mimic the sounds produced by the queen ants of their hosts to elicit food, care and even rescues, at the expense of the colony’s own offspring. Go to “Caterpillar noise tricks ants into service” article at Science News to actually hear the sounds the caterpillars and ants make. Edit: Hear the audio links here at Science.
Drumming
I studied carpenter ants, and whenever I opened a nest, I could hear the ants react. The workers strike their mandibles and gasters on the surface of the tunnels in their wooden nest to create a drumming sound. Ants deeper in the nest rush to the site of the disturbance and assist their sisters with defending the nest.
Rattling
The rattle ants of Australia also tap their gasters when they encounter an enemy intruder, such as a bird feasting on their nestmates. They live in leaf nests high in trees. The leaves may be slightly dry and the tapping produces an audible rattling sound that gives these ants their name.
Rattan ants of Asia live in thorny rattan vines. When an intruder gets too near their nest the ants hit their mandibles against the stem of the plant. Because they hit in a synchronized way, the sound pulses. (I was interested to learn that some katydids also drum or vibrate the plants, especially species that stay hidden deep in foliage. )
Where are the ants’ ears? No one knows for absolutely sure how it all works. Some ants have ways to detect surface vibrations in their legs. It is also likely that certain ants use hair-like sensors in the tips of their antennae. When the hairs are displaced the ants detect signals that are called nearfield. Those are signals from sources that are extremely close. The ants remain completely unaware of sounds produced by far objects, like us shouting at them for example.
In any case, as our human sound equipment becomes refined, I’m sure we will be hearing more from ants.
Bug Bytes, the USDA Sound library of Richard Mankin, has a number of ant recordings.
References:
Barbero, F., J.A. Thomas, S. Bonelli, E. Balletto, and K. Schönrogge. 2009. Queen Ants Make Distinctive Sounds That Are Mimicked by a Butterfly Social Parasite. Science 323 (5915) 782.
Donato A. Grasso, Marco Priano, Gianni Pavan, Alessandra Mori, Francesco Le Moli. 2000. Stridulation in four species of Messor ants (Hymenoptera, Formicidae). Italian Journal of Zoology, Volume 67, Issue 3: 281 – 283
