Mosquitoes are the most dangerous animals on the planet. They cause no end of anxiety for people at risk of mosquito-borne disease. With the leap of Zika virus into the international public health spotlight this year, we’re reminded once more how threatening these otherwise fragile insects can be.
But a battle rages in Australian backyards each summer that all too often escapes our attention. There is a fight between the “good” and “bad” mosquitoes for our pot plant saucers and bird baths, our roof gutters and rainwater tanks – and, most importantly, our blood.
Mosquitoes are incredibly adaptable creatures. They’ve adapted to almost every aquatic environment on the planet, from coastal rockpools to snowmelt streams and polluted drains to pristine wetlands – everywhere, in fact, apart from the open ocean.
Not only will you find mosquitoes in all of these environments, but you’ll find some mosquitoes specifically adapted to these unique habitats.
There is no better example of the adaptability of mosquitoes than in our own backyards.
There’s a suite of mosquitoes found in tree holes and water-holding plants. They lay eggs at the edges of the small pools of water collected in the nooks and crannies of trees or in leaf axils (the tiny point where the leaf joins the stem). Some mosquitoes have even adapted to life in pitcher plants. While many of them are still found in these habitats, others have given up the swamps and forests for our suburbs.
As people intentionally, or unintentionally, started storing water around the home, mosquitoes took the chance to exploit these unoccupied niches. The plastic takeaway food container, the tyre, the bird bath and rainwater tank have all been embraced by mosquitoes, not only as homes but also as a way to hitchhike from one country to another.
There is little doubt that some mosquitoes arrived in Australia for the first time along with European explorers, their eggs hidden away in the cracks and crevices of water barrels. Mosquitoes have kept coming to Australia by air and sea, hidden as eggs on cargo and personal belongings.
The most recent arrival, Aedes albopictus, is a major cause for concern and may influence future mosquito-borne disease risk. However, some “home-grown” mosquitoes are already flourishing in our suburbs.
There are “bad” mosquitoes…
Australia has plenty of native mozzies but Aedes notoscriptus probably bites more Australians than any other mosquito. It is widespread across the country, from Darwin to Hobart and from Brisbane to Perth. We’ve even exported it to California! It is active most of the year, disappearing only in the particularly cold months.
It is found in close association with water-filled containers and water-holding plants (particularly bromeliads). The mosquitoes lay eggs around the edge of the water. Then, as water levels rise, the eggs are covered and the larvae (commonly known as “wrigglers”) quickly hatch out.
It may then take only a week for adult mosquitoes to emerge from the water. They don’t fly much more than 200 metres from their favourite habitats. So, if you provide a nicely shaded backyard with plenty of water-holding containers, there isn’t much need for them to move on.
This mosquito is rarely very abundant but it readily bites people. It tends to be more active in the mid- to late afternoon – perfect timing to disrupt backyard activities in the cooler parts of the day.
It has also been implicated in the spread of Ross River virus, so it’s more than just an annoying nuisance. It can even infect our pets with dog heartworm.
…but also “good” mosquitoes!
Pest mosquitoes such as Aedes notoscriptus may be annoying to us, but they’re a delicious treat to one predatory mosquito.
Toxorhynchites speciosus is as “good” a mosquito as there can be. First, it is a gorgeous creature. Almost four times the size of a typical mosquito, it is a large dark and shiny mosquito with bright metallic patterns. But they’re not just good-looking.
This is one of the few mosquitoes that don’t need blood. Unlike almost all other mosquitoes, the females of which need blood to develop their eggs, Toxorhynchites speciosus doesn’t bite.
It gets its energy from plant juices and nectar. Its long, curved proboscis is a giveaway to its sugar-feeding lifestyles, and is a friendlier visage than the needle-like proboscis of most other mozzies.
The good news doesn’t end there. Not only are they not pests themselves but the larvae of Toxorhynchites speciosus are predatory and feed on the wrigglers of other mosquitoes found in water-holding containers. In some parts of the world, a closely related mosquito is used as a biological control agent of the pests that spread dengue, chikungunya and Zika viruses.
While Toxorhynchites speciosus will chomp through plenty of wrigglers of Aedes notoscriptus each summer in Australian backyards, it is unlikely to make a huge difference in bites. However, next time you see a “giant mozzie” buzz by, think twice before you squish it.
If you want to keep the pest mosquitoes out of your backyard, make sure you get rid of any water-holding containers. If you can’t throw them out, keep them covered.
Check to make sure your roof gutters and drains are clear of leaves and other debris so they flow freely. Check your rainwater tank is screened to stop the mozzies entering. And try not to kill the good guys who help keep the other mozzies at bay!