April 2013 Archives

Hi,

I'm developing some educational materials on ecology for high school students in western Montana. As a small part of the project, I'd like to help the students to expand their idea of "population" to organisms other than human. So I am including information on the number of people (~91000), cattle (~13200), trees (~1.2 billion), bears (still waiting on that number), and would love to include an estimate of the number of ants! This is an area in northern Montana (Flathead County), mostly forested, some urban, and some agricultural... also some sagebrush steppe. Can you suggest a way for me to estimate the ant population within a couple of orders of magnitude? More than a trillion, perhaps? Any guidance would be welcome. Thank you!

Jane

**********
Dear Jane,

Thank you for contacting AntBlog. We are glad to hear you are including ants in your ecology high school materials. Your question is related to a question we addressed regarding biomass:

http://www.antweb.org/antblog/2010/10/do-ants-really-have-the-largest-biomass-of-all-species-on-earth-laurie-usa.html

In summary, estimating the number of ants alive right now in Flathead County, Montana is likely impossible. But, you if you assume that all the ants alive today in Flathead County weigh as much (and likely more since Montana has a low population density) than all the humans in Flathead County, Montana. So if you calculated the average weight of a human and multiplied it by the number of humans and then took that number and divided it by the average weight of an ant, this would give you an estimate for the number of ants alive today. Here is my back the envelope calculations of this formula using average adult weight (which is likely a bit to high for the average of all humans if you include non-adults) and an "average" weight for an ant (which varies immensely between ant species - think of calculating an average weight of mammals from species as small as mice to as large as elephants - that is the equivalent in the size ranges of ants):

Number of ants in Flathead County, Montana:
91000 humans x 150 lbs. average weight of a human = 13,650,000 lbs. of humans in Flathead County, Montana

1.5 mg (= 0.0000033069 lbs.) average weight of an ant

13,650,000 all human weight / 0.0000033069 single ant weight =

4,127,732,922,072 ants alive in Flathead County, Montana today


Number of ants on Earth:
If we do the same exercise for all the ants alive on the planet, here is what you get:
7,077,551,385 human on the planet x 150 lbs. average weight of a human = 1061632707750 lbs of humans on Earth

1.5 mg (= 0.0000033069 lbs.) average weight of an ant

1061632707750 all human weight / 0.0000033069 single ant weight =

321,035,624,829,901,000 ants alive on the planet today


That is a lot of ants!


On a related note, you might be interested in this blog post (and many others - feel free to read through them) on why ants are important in the environment for your ecology materials:

http://www.antweb.org/antblog/2012/08/what-good-are-ants-david-panama-city-florida-usa.html


Best regards,
Corrie Moreau & the AntAsk Team


Hi,
I've just read your web article about ant communication, which interests me. When I was a child in Africa I saw two species of ants fighting in my garden - small black ants (that we called sugar ants as they were always after the sugar!) and much larger red ants (about 7 - 8 times the size of the black ants and with a fearsome bite). The black ants were attacking the red ant nest at a distance of about (I have to estimate this, but based on a wide turning circle for cars) 15 - 20 yards. As I bent over the red ant hole watching the battle I saw them bringing their queen up to the surface. I picked the queen up and carried it to the black ant nest to see what would happen. For a little while nothing happened; the black and red ants at the red ant hole continued their battle, and the black ants around their hole ignored the red queen completely. Then one of them "spotted" the red queen, and within 10 seconds or so a host of them came boiling out of their nest and began dragging the queen down their hole. At exactly that moment the red ants gave up the fight and turned and "ran for it" away from the black soldier ants. Now there must have been some communication from the red queen to her soldier ants, presumably a distress call, and possibly also communication between the black ants - but across a distance of at least 15 yards. That communication was too fast to have passed between ants travelling between the two, and anyway they were all black ants. I assumed at the time it must have been chemical pheromones, but it carried across a fair distance given the size of the ants, and I wonder if anyone else has any experience of anything similar?

RDL of the U.K.


Hello RDL, and thank you for this inquiry.

Given that childhood memories can be a little treacherous, I'll still take a try to respond to this as best I can. My first thought is that perhaps you conflated the "sugar ants" (I'm guessing the common human-associated ant Paratrechina longicornis) that abounded where you live, with a less common, small, dark-colored ant that may have been one of the lesser army ant species that inhabit much of Africa (genus Aenictus). Unlike the larger and more famous driver ants of the genus Dorylus, Aenictus workers are closer to a uniform size and lack the large-headed, saber-toothed soldier caste. These ants feed primarily on other ants' brood, and may also carry home stunned, live adults to be consumed by their colonies. I think that's the behavior you observed.

Okay, that was just guessing, but this part will be more based in science. Regarding your pheromone question, I think it may rest on the common, anthropomorphizing misconception that the queen is a sovereign that "rules" the colony. While it is true that the queen health and reproductiive state influence the health and behavior of the colony, she does not in any literal sense tell the colony, nor any individuals within the group, what to do. The presence of the queen in the nest is thought to be sensed by pheromones disseminated through the colony. Likewise, her absence is eventually sensed in the colony by the decrease, and finally, complete lack of her pheromones being spread through the population. It is possible that the colony of larger ants that was attacked by the smaller black ants sensed that their queen had gone missing, but I deem it rather more likely that their behavior was something apart, more on the order of an alarm/panic response to the invasion itself, and had nothing to do with the queen's presence, absence, or attempts to communicate with her daughter workers. It is not concurrent with what we know about ant communication by pheromones that a "distress call" was sent out, certainly not one that could be detected at a distance of 50 feet away by the workers. A common feature of the physical chemistry of fast-acting pheromones is that they diffuse very rapidly, and over very short distances, to the point where they quickly become no longer at suffcient concentration to elicit a response. Further, no ant seems to be able to aim peromones in a particular direction, least of all at 50 feet distance. On the other hand, ant colonies not uncommonly have an panic escape respone to invasion by army ants, or even to any other sort of ant that invade their nest em>en masse.

Best regards, James C. Trager of the Ask Ant Team