The forests of Denver, Colo., are currently under attack by an invasive insect species from Asia. So what is the scientists’ plan to stop this assault on trees? They’re going with the controversial move of introducing a second invasive species to destroy the first one. If it sounds like that children’s song about the old lady who swallowed the spider to catch the fly, that’s because it basically is. Unleashing a second non-native species might help to eradicate the first species, but it can also unleash a series of other consequences . Previous experiments in this invasive species vs. invasive species tactic have worked out with various degrees of success, as these four examples will show.

The forests of Denver, Colo., are currently under attack by an invasive insect species from Asia. So what is the scientists’ plan to stop this assault on trees? They’re going with the controversial move of introducing a second invasive species to destroy the first one.

If it sounds like that children’s song about the old lady who swallowed the spider to catch the fly, that’s because it basically is. Unleashing a second non-native species might help to eradicate the first species, but it can also unleash a series of other consequences. Previous experiments in this invasive species vs. invasive species tactic have worked out with various degrees of success, as these four examples will show:

1. Ash Whiteflies vs. Wasps

In the late 1980s, ash whiteflies started taking over southern California. The pests are known to devastate fruit crops, and once their population grew, they took a real toll on the region’s citrus production.

Initially, scientists thought the whiteflies had no natural predators, until researchers discovered that certain wasps loved to feast on the whiteflies larvae. Accordingly, entomologists released hundreds of wasps throughout the area to prevent so many whiteflies from hatching. Research published in the California Agriculture journal later deemed the experiment a “success” since it helped to decrease the populations of four (out of eight) species of whiteflies that were dominating in southern California.

2. Rabbits vs. Ferrets and Weasels

In the 1800s, New Zealand decided to intentionally import rabbits to its country from England. The idea was to have a new animal for people to eat and hunt, but the rabbits soon bred like… well, rabbits, and the population was out of control.

With too many bunnies destroying their crops, farmers advocated shipping in predators of the rabbits to keep the population in check. In the UK, ferrets and weasels naturally preyed on rabbits, so they brought in many of them. Unfortunately, this new invasive species didn’t do a good job of taking out the first invasive species. Instead, the ferrets and weasels found easier meals in the native New Zealand birds, many of which are flightless.

Now, New Zealand has a bunch of non-native species wiping out the native species. The country has set up a lot of traps to catch these animals in an effort to spare the actual New Zealand creatures. If they’re smart, they’ll stick to the traps and not try introducing any new animals. I bet tigers would eat weasels!

Read the other two examples at ENN affiliate, Care2.

Cane toad image via Shutterstock.