Written by Joe Ballenger
— Suzanne Geiger (@slvrfnx) December 15, 2014
One of our first submissions asked what gnats do for the ecosystem. We originally answered this question on Twitter, and you can view the resulting conversation here.
It’s a difficult question to answer, because the word ‘gnat’ essentially means small fly. Flies are a really big and complicated group of insects, so it can mean a lot of things. Generally it’s used to refer to one of several groups of somewhat primitive flies, many of which feed on fungus or plants. These flies play an important role in the ecosystem as decomposers, or to regulate plant populations.
Other times it’s used to refer to any particularly small fly, usually those which swarm around people during the summer…but not always. The flies which swarm around people are typically males, and boy flies have a tendency to gather around tall objects which serve as a place for them to meet females. They’ll follow people around and will usually act as a harmless annoyance, unless they feed on eye exudates. These guys can vector pinkeye.
In the Wikipedia article, about one third of the flies known as gnats have a lot of species which feed on blood. These families include biting midges, sand flies, and mosquitoes. Although there are a lot of really neat flies, the bloodsucking varieties have been in the news as of late because of some plans to release transgenic mosquitoes in Florida.
This is actually a wonderful idea despite what the media says, and we’ve got a post in the works about this very topic. However, before we jumped into discussing the GMO mosquitoes, we wanted to talk a little bit about the ecology of parasites.
So…what do bloodsucking insects do for the ecosystem?
The majority of this article is a reiteration of this op-ed which appeared in Nature News awhile back. There are some major issues with the article, which we will discuss further at a later date, but the information about mosquito ecology is actually pretty solid. Mosquitoes and other biting insects play a huge role in the ecosystem. For instance…
Mosquitoes act as a taxation system
Bloodsucking insects, particularly mosquitoes and biting midges, play a really important role in most ecosystems by providing a kind of taxation service. They remove a lot of blood from animals, and transfer that blood into lower levels of the food chain. They also transfer this biomass into different environments. In effect carbon from grass eaten by a deer could end up back in a pond, thanks to a mosquito who fed on the deer and laid eggs in the pond. The larvae could then be eaten by a fish, which could then be eaten by a bird…they serve as a very important part of the food chain.
In addition to facilitating the transfer of biomass, diseases spread by bloodfeeding insects help regulate wild animal population. The Tsetse is a fly found in Africa which vectors Nagana, a form of sleeping sickness. This disease has decimated the livestock industry in many parts of Africa and has created so-called ‘green deserts’ where susceptible animals-including humans-can’t live. It’s estimated to cost livestock farmers in infested regions about $2.5 billion per year in a region that is recognized as one of the poorest in the world. Wild animals are important in the transmission of sleeping sickness, but are a bit more resistant than humans or domestic cattle.
Also…to reproduce, the tsetse gives birth to tsetse sized maggots which turn straight to adults. So there’s some interesting biology happening in this group of flies, as well.
Predators and pollinators
Not all mosquitoes are parasites. Toxorhynchites is a genus of non blood-feeding mosquitoes. The larvae are important predators, and play a significant role in regulating mosquito populations as a natural biological control. In fact, a male of this genus was used in the movie Jurassic Park when the scientists were looking for dinosaur DNA.
We’ve already discussed how some blood feeding insects are important to agriculture because of their role as pollinators in chocolate production. It should be mentioned that there is no mosquito species where males feed on blood. All male mosquitoes feed on nectar, and likely play at least a minor role as pollinators in swamp ecosystems.
Also at least one genus of mosquito, Wyeomyia, actually lives inside pitcher plants. It probably plays a role similar to the equivalent of an intestinal parasite by eating the contents of the pitcher plant’s ‘gut’.
Blood-feeders are an environment
As a final point I think something should be said about insects and their microbiota. Arthropods vector hundreds of diseases, from bacterial diseases like plague to animal diseases like lymphatic filariasis. It’s not uncommon for an insect to be exposed to more than one disease at a time, a process known as ‘superinfection’.
Surprisingly, superinfection does not always result in the insect vectoring more than one disease. More often, it seems one disease will outcompete the other. How this happens isn’t very well understood, but it’s thought that viruses compete for resources within the mosquito. There are also bacteria, like Wolbachia, which affect the mosquito’s ability to transmit disease by modulating the immune system. Gut bacteria can play a role in the transmission of malaria, as well.
So what does this mean? In addition to being an important part of the environment, bloodsucking insects are also an environment in and of themselves where microbial life-and-death struggles take place on a constant basis.
When all is said and done, I actually feel a bit of sympathy for these creatures. Not all mosquitoes carry diseases, and a lot of the ones that do aren’t native to the environments where they’re found. I even feel sympathy for the disease vectors, because the diseases they carry can make them sick as well.
They’re not our enemies per se, but they’re interesting animals which are held hostage by their illnesses. As annoying as they are, I can’t bring myself to hate them.
Mosquitoes and other blood feeding insects are an important part of the environment. They’re food for a lot of animals, and they help regulate animal populations. Some mosquitoes are even good at eating other mosquitoes. Within the mosquito, there are also entire microbial communities which compete with one another just like the mosquito competes with other animals for it’s survival.
Because mosquitoes are really important disease vectors, sometimes we need to control their populations. There are some new techniques which are being invented to do this in a smarter way, and we address this in our next post…The Truth About GMO Mosquitoes.