Don't eat the cane toad! Kesler Science Weekly Phenomenon and Graph

Australia's yellow-spotted monitor is a lizard you wouldn't want to mess with. It stretches out to 5 feet long, has a vicious, venomous bite, and sits on top of the Australian desert food chain as an apex predator. 🐊 So why are their population numbers plummeting? 🤔

To answer this question, let's go back to the 1930's. A lucrative crop grown in Australia at that time was sugarcane. The sugarcane was under attack by beetles native to the area. This type of beetle would lay eggs and hatch as larvae underground, damaging the root systems of the plants. This made it tough to exterminate the pests using traditional methods. 

A plan was made to bring in a species of animal that would find just such a beetle a tasty treat. Enter Bufo marinus, or the cane toad of South and Central America. Unfortunately, what started off as a clever plan to avoid chemical pesticides turned into an ecological problem that spiraled out of control. 

The cane toad's biggest adaptation is it's ability to produce a deadly toxin as an adult. This bold toad will not run away from predators, almost defying them to take a bite. When predators like the yellow-spotted monitor do consume the cane toad, it doesn't take long for the toxin to take its lethal toll. The monitor lizard is not the only predator suffering the effects of the invasive toad species. Scientists have noticed that native birds, turtles, and even crocodiles are dying off due to the toxic toad. 

What's wild is, within the 90 years that the cane toad has been living in Australia, it has had some major adaptations. Cane toad legs have been growing larger, which allows them to travel up to 37 miles during migration. In 2023, a behemoth female cane toad was uncovered and brought to a museum. The monster was affectionately called, "Toadzilla," weighing in at 6 pounds!!

What started off as several thousand toads in the 1930's has ballooned into a population of more than 200 million. The worst part? There has been no noticeable difference in the sugarcane beetle population. 😖

Scientists aren't really sure on how to tackle the cane toad problem in a humane way. Ideas like introducing sterile males to compete for resources or genetically modifying the toads have all been proposed, but nothing has been put into motion yet. 

The good news is that there's hope for the predators like the yellow-spotted monitor. These lizards are smart, and scientists have been experimenting with training the monitors. They expose the monitors to cane toad eggs and tadpoles which have just enough toxin to make the lizards sick, but not enough to kill them. Monitors in the experiment learn to avoid the adult cane toad and seek out other prey instead. 

Australia is no stranger to invasive species. The government faces the cost created by these organisms, costs caused by trying to get rid of those species and by fixing the damage they cause. Check out the graph below:

If I wanted to bring this graph to my students, I'd prompt them with questions like:

💡Which is the most expensive Australian invasive species to deal with according to the graph? Why do you predict this is the case? Cats rack up the highest bill at almost $19 billion. This may be because of harm to bird populations or efforts to control feral cat populations. 

💡Which insect is the most costly? Fire ants are the most expensive insect.

💡Why might governments spend money to deal with invasive species? Students might predict that money is spent to protect crops, avoid fires, or to prevent native species from dying off. 

Your students might be shocked to see the impact of invasive species on the ecosystem AND the economy!