Invasive Species

About 100 years ago, sugar farmers in Puerto Rico faced a big problem. Cane beetles were eating their sugar cane crops, and this was a problem in many places. To tackle the beetle problem, scientists introduced a large, bug-eating toad called the cane toad.

Cane toads are originally from tropical areas in Central and South America. These toads are poisonous and known for their big appetite. They usually feed on insects and small animals, like lizards and rodents. In the early 1900s, people brought cane toads to Puerto Rico to eat the cane beetles and protect the sugar cane crops – and it worked!

After success in Puerto Rico, cane toads were taken to many other countries, including Australia, to deal with pests. In Australia, thousands of cane toads were released over several years. Sadly, the cane toads didn't control the beetle population, and, even worse, they ate many important native species.

As invasive species, cane toads changed the native food web and outcompeted native toads for food. Few predators could eat them because of their poisonous skin, so their population kept growing.

Today, cane toads still pose a threat to native species in many countries and are seen as one of the most troublesome invasive species in the world.

More than 70 years ago, a small island called Guam was full of songbirds, lizards, and many other small animals. With lots of food and few predators, these animals had the perfect habitat! However, this all changed when venomous brown tree snakes accidentally came to Guam. 

Scientists hypothesize they probably arrived from Australia on a large ship. The brown tree snakes quickly moved across the island, causing lots of problems as their population grew. They ate a lot of native birds and lizards, causing many of them to become endangered or extinct. They crawled across power lines, causing the power to go out often. They also started living near people, putting pets and kids in danger because of their venom.

Since very few predators could eat the brown tree snakes in Guam, scientists and local people started catching and removing them. Scientists even dropped poisoned rats onto Guam to try to get rid of the brown tree snakes. Although these strategies helped reduce their population, brown tree snakes are still causing problems on Guam to this very day.

Today, the population size of brown tree snakes in Guam is shrinking mainly because they are running out of food. Still, scientists are working on ways to keep native birds and reptiles safe. They also use search dogs to find brown tree snakes on ships and planes to make sure they don't become invasive and cause the same problems on other islands.