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Apple Snails & Tiger Mosquitoes

Apple Snails & Tiger Mosquitoes Photo Credit: James Gathany/CDC

In Florida, invasive, disease-carrying tiger mosquitoes are breeding in the shells of an invasive snail.


Transcript

Invaders exploiting invaders. I'm Bob Hirshon and this is Science Update.

In Florida, Asian tiger mosquitoes are getting a leg up from an invasive South American apple snail. This according to entomologist Nathan Burkett, of both the University of Florida and the University of South Florida. He's found the tiger mosquitoes breeding in the empty shells of the invasive snails. What's more, they're doing it in habitats very unlike their usual haunts in their native Asia.

Burkett:
One of the remarkable things from the aspect of the biology of this mosquito is this is a peri-urban mosquito. It is accustomed to living and breeding in close association with human beings. And some of these locations that I surveyed, I had to get to by kayak.

These mosquitoes seem drawn exclusively to the apple snail shells, which native mosquitoes in the same area ignore. It may be the first known case of two species from different parts of the world developing such a relationship in a third location. I'm Bob Hirshon for AAAS, the Science Society.


Making Sense of the Research

An “invasive” species is a species that isn't native to a particular ecosystem, but came to it from another place. They often disrupt the balance of life in the area they invade. For example, they may prey on native plants and animals that have no defenses against the invaders. 

Invasive species aren't a new phenomenon; as long as humans have traveled the world and traded with other cultures, some creatures have hitched a ride on the journeys, sometimes gaining a foothold in a completely new territory. However, over the past century, species' invasions have become far more common than ever, thanks to factors like great increases in global travel and shipping, climate change (which drives or forces some species beyond their usual range), ecological damage (which may destroy a species' natural habitat), and more. 

The two species involved here are a snail and a mosquito. Both came to Florida and the American Southeast from very different places: the apple snails hail from South America, while the tiger mosquitoes come from Asia. So far, the snails haven't caused any obvious problems, but the mosquitoes are responsible for spreading exotic viruses and parasites that were previously unseen in the United States. 

The snails are passive partners in this relationship, since their shells become useful to the mosquitoes only after the snail gets eaten. Typically, they're eaten by a native, crane-like bird called the limpkin, which itself has been venturing far beyond its usual Everglades habitat to feast on the invasive snails. Limpkins nab the invasive apple snails from the water, bring them up on land, and eat them, often leaving a pile of snail shells behind.

Burkett's team found that the invasive tiger mosquitoes breed in tiny pools of water that collect in these empty shells. Other, native types of mosquitoes in the same area breed in other small objects that collect rainwater, from tree holes to soda bottle caps. But Burkett found that the native mosquitoes ignore the invasive snail shells, while the invasive snails avoid the native mosquitoes' breeding areas. 

Furthermore, the invasive mosquitoes are taking advantage of these shells far out of the comfort zone that they generally stick to in their native Asia. There, the tiger mosquitoes are found mainly in cities and their immediate surroundings. In Florida, though, they're breeding in remote areas far from human habitation. 

Relationships like this are found all over the animal kingdom. But this may be the first known case of two invasive species, each from a different part of the world, finding each other in a third part of the world and developing an interconnected life cycle. The fact that this one exists, though, suggests there may be others we don't know about.

Now try and answer these questions:

  1. What is an invasive species?
  2. What are the two invasive species in this story? Where are they each from?
  3. How does the invasive tiger mosquito depend on the invasive apple snail? Why is this unusual?
  4. What else is unusual about the way Asian tiger mosquitoes have adapted to life in Florida?

You may want to check out these related resources:

The Science Updates Giant Snail Invasion and Everglades Pythons tell about two invasive species wreaking havoc in Florida.

The Science Update Litter Life describes how some invasive species may be reaching distant shores by riding on ocean trash.

In the video BioBlitz BobCast 2: Controlling Invasive Plants, meet National Park Service biologist Jamie Evans, who's working to control invasive plants in Rocky Mountain National Park.


Going Further


For Educators

The Science Update lessons Giant Snail Invasion and Everglades Pythons tell about two invasive species wreaking havoc in Florida.

The Science Update lesson Litter Life describes how some invasive species may be reaching distant shores by riding on ocean trash.

In the video BioBlitz BobCast 2: Controlling Invasive Plants, meet National Park Service biologist Jamie Evans, who's working to control invasive plants in Rocky Mountain National Park.


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