Earlier this year, South Australia’s wheat growers in the Yorke Peninsula had one of the worst mouse plagues on record. Thousands of mice ate seeds that had been sown by farmers. The areas to the south and east of Australia are the worst places in the world for mouse plagues.
Have you ever had a mouse in your house? Maybe you keep them as pets. They live in nests close to food, and can fit through a hole the size of a pencil by nibbling at the edges and squeezing their body through the small space.
Having lots of mice is a problem. They can spread diseases that cause food poisoning and they chew through furniture. On farms, they can cause big problems because they mainly eat seeds, such as wheat.
“They do massive damage throughout the farming year,” says Steve Henry from CSIRO. “If they are there when crops are sown in autumn, they eat the seeds out of the ground so there are no plants. If they are there at harvest time, they will actually climb up the stalks and eat the grain. They can also damage stored grain.”
A mouse plague is when more than 1000 mice are found in a hectare of land, that’s 10 000 square metres. If conditions are right, a few mice one year will multiply into a huge horde the next. Mice breed really fast, a mouse can have up to ten pups every three weeks!
The best way to battle a plague is to stop it before it starts. For that, we need to notice when mice numbers first start rising.
Last month, a new website was launched to let farmers map mouse activity from their field with their mobile phone. MouseAlert combines the data from the local area and shares it with people across Australia, as well as researchers.
“The MouseAlert website provides us with data to better predict mouse plagues,” says Steve. “If we can predict plagues better, people can put mouse bait out before it gets bad.” Other ways to control mouse numbers are to store grain safely and keep the farm clean from spilled grain. As spring begins in Australia and mice start breeding, we need to keep an eye on their numbers. A few small mice might be the start of a big problem.
Mouse plagues in the grain-growing regions of Australia cause problems for farmers and communities. Image: Grant Singleton, CC-BY
Quiz questions
How is explosive trinitrotoluene better known?
Which body part do butterflies use to taste?
What is photonics the study of?
Which country owns Antarctica?
Approximately how much of the human body is water? Is it a) 25 per cent, b) 60 per cent, or c) 90 per cent.
Try this: Growth game
You will need these things.
Start with two chocolates on the plate.
Roll the dice. If you get a 4, 5 or 6, double the chocolates on the plate. Keep a record of how many chocolates or 'mice' you have.
Keep rolling the dice and adding or removing chocolates, according to the rules.
When you run out of chocolates to add to the plate, you lose!
You will need
Pen and paper
Dice
Chocolates such as Smarties or M&Ms
A plate or tray. Optional: Decorate it to look like a farm
Rules
Roll a 1 – Farmer puts out mouse traps. Remove five chocolates. Roll a 2 – Farmer stores grain safely. Do nothing. Roll a 3 – Patch up holes in grain storage area. Do nothing. Roll a 4 – Great harvest. Double the number of chocolates. Roll a 5 – Extra rain. Double the number of chocolates. Roll a 6 – Mice get into grain storage. Double the number of chocolates.
What to do
Make two columns on your piece of paper. Title one column as ‘month’ and the other as ‘mice’.
Start off by putting two chocolates on the plate. This represents two mice in the field. Keep a note of this on your piece of paper by writing the number 1 in the month column and the number 2 in the mice column.
Write the number 2 in the month column, and roll the dice to see what happens to the farm in that month. Follow the rules above and change the number of chocolates on the plate. Keep a note of the number of chocolates in the mice column.
Keep playing the game, adding a month and rolling the dice each time. If you get rid of all the mice, you win! If you put all the chocolates on the plate, there’s a plague of mice and you lose!
To extend this activity, draw a graph to show how the number of mice changed over the months.
What happens if you, the farmer, notice a plague starting and act fast? Try changing the rules. Now when you roll a 2 or a 3, the farmer puts out mouse bait. Remove five chocolates.
What’s happening?
This is a model of a mouse plague. Plagues are more likely to start after a great harvest of wheat, or if extra rain falls between April and October. Farmers can prevent plagues by storing grain carefully, cleaning up any spilled grain in the fields and making sure mice can’t get into the store rooms.
When the number of mice is small, you may be lucky and roll a 1 to win the game. But once the number of the mice is high, it becomes very hard to win. Doubling the number of chocolates soon adds up. From 2 to 4 to 8 to 16, 32, 64, 128, 256, 512 ... then you’re over a thousand and unless you’ve got a huge bag of chocolates, you’ve lost! This is called exponential growth. It starts slowly, and the bigger the population gets, the faster it grows.
Applications
Mouse plagues occur in the southern and eastern grain belts of Australia. During a plague, there are over 1000 mice in a hectare of land. They can do a lot of damage to crops and spread diseases.
By noticing when there are a lot of mice and recording sightings on the MouseAlert website, people can take quick action to stop a plague before it starts.
Other examples of exponential growth include the number of bacteria in a Petri dish, and the number of people in the world.
After ten years of flight, the spacecraft Rosetta has arrived at the comet 67P/Churyumov-Gerasimenko. In November, it will release a lander onto the surface of the comet to study what the comet is made of. The European Space Agency recently announced the landing site. Get the latest updates on the Rosetta blog.
See it!
Snow-capped mountains sleep as the northern lights paint the sky in green. See the winners of the 2014 Astronomy Photographer of the Year, by the Royal Museums Greenwich.
Watch it!
Cats, dogs and birds see the world differently to people. The RiAus investigates vision in the animal kingdom in A Week in Science.
Quiz answers
Trinitrotoluene is also known as TNT.
Butterflies taste with their feet.
Photonics is the study of light.
No country owns Antarctica. It is considered a scientific reserve.
b) Approximately 60 per cent of the human body is water. It varies between people, but tends to be between 55 per cent and 75 per cent.
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