Do ants really have the largest biomass of all species on earth?
Like many questions in ecology, this question has a few different kinds of answers: short, long, and "are you asking the right question?" I'll give them to you in order, as best as I can.
Long: In their book "Ant Ecology," Lach, Parr, and Abbott (2010) quote Holldobler and Wilson (1990) in saying that "The estimated 10,000 trillion individual ants alive at any one time weigh about as much as all human beings combined." But the main reason the answer to your question is "no" is that ants are not a single species (please see an earlier post about how many species of ants there might be). Ants are a taxonomic family with more than 14,000 described species and subspecies, so it's really unfair to compare their biomass with, say, leopards or bull frogs. Or humans or Antarctic krill.
There are several studies out that indicate that ants are a very important part of ecosystems where they occur. The biomass of ants in tropical rainforests is thought to often be greater than that the biomass of all vertebrates in the rainforest combined. But the measurements necessary to make claims like these were really only taken in a few studies. (one such study, Fittkau and Klinge 1973, is linked here, and a study that assesses ant prevalence in tropical rainforest canopies, Davidson et al. 2003, is linked here ) It is very time-consuming to count all the dead ants that fall out a tree after you have fogged it with insecticide, so comparable studies have not been done in many parts of the world.
It is important to note (much as it pains me, as a myrmecologist) that the world-wide population of termites has been estimated at about 27 times higher than the ant population in a paper by Zimmerman et al. 1982. (linked here) Although I don't know what the average biomass of a termite is, I suspect that it is not 27 times less than your average ant, so termites are also in the running for insect group with the most mass. I think that the population estimates and biomass estimates for both insect groups, however, are very rough, and either could be off by a decimal place here or there. Because this is AntWeb, I'll say that the issue of who has more biomass, ants or termites, is up for debate. A more isoptera-centric blog might argue otherwise.
Worldwide biomass estimates for individual species are very difficult to come by. The most rigorous estimates are for humans and domesticated animals. There are probably a little more than 6.7 billion humans alive right now, and together, we might weigh as much as 335,000,000,000 kg (or 737,000,000,000 lbs.) This figure is based on an average human weight of more than 100lbs, though (50kg, to be exact). I don't know how accurate this estimate is, especially considering that about 1/3 of us are children. There are supposedly around 1.3 billion cattle in the world, and, put together, they may weigh almost twice as much as our species.
The only non-domestic, super-abundant species for which serious attempts have been made at estimating biomass is a type of shrimp that lives in the cold waters around Antarctica: the Antarctic krill, Euphausia superba,. They are the primary food for many fish and baleen whales (suborder Mysticeti). In a really interesting study (click here for more) Atkinson and colleagues (2009) calculated the world biomass of krill to be between 117 and 379,000,000,000 kg (note that the upper estimate is slightly above what people have suggested for the total human biomass). Truly, these organisms are successful. They might be the only wild species that could compete with Homo sapiens for the title of "species with the most biomass."
However, we can't forget that as much animal biomass as there is, there is even more plant and bacterial biomass. Probably at least ten times as much as the biomass of all animals put together. Scientists still argue about which has more biomass on earth: bacteria or plants. Worldwide, they both probably have about the same amount of Carbon, but Bacteria probably contain about 10 times more Nitrogen and Phosphorus (read more here ) Like ants, though, there are many many species of bacteria and plants, and I don't know of any studies that attempt to estimate world-wide biomass for a single species of either.
"Are you asking the right question?" In ecological studies, there has been a lot of emphasis placed on using biomass as an indication of an organism or group of organism's importance in the ecosystem. However, what is at least as important is how quickly organisms use resources. For example, because they have higher metabolisms, a million ruby-throated hummingbirds will consume much more food than one African Elephant, even though both have about the same biomass (3,000kg, or 3.3 US tons). Thus, ants, as a group, may actually consume more resources per year than antarctic krill, even though both may have roughly the same biomass, because ants tend to be smaller, and live in warmer environments. Although there may be about 10-15 times the biomass of termites than cows in the world, studies have suggested that termites might produce almost 30,000 times as much methane per year because of their faster metabolism. Humans are larger than ants and krill, and so should have slower metabolisms, but I'm sure we have a much larger ecological footprint than either species, and thus have much more of an impact on our environment. When you factor in all of the oil and coal we use in industry and our daily lives, we are definitely the most ecologically significant animal taxon.
I hope this helps. Sorry if it got a little preachy towards the end.
Jesse Czekanski-Moir & the AntAsk Team