Locusts What can strip a field of crops down to the soil in a few minutes (a swarm of locusts)? What is a locust (a type of grasshopper)? Where do they live (southern Europe, Africa, North and South America)? A swarm of bees is small, but how big is a swarm of locusts (can be 600 to 1,600 or more square kilometres: imagine a square 25 or 40 kilometres each side, and the area that it would cover locally)?

Migration Why do creatures migrate (looking for food; avoiding overcrowding; finding a better climate; breeding, eg, to lay their eggs)? What creatures migrate (locusts, beetles, birds in summer and winter, butterflies which will fly up to 100 kilometres a day)? Humans also migrate (emigration to America, Canada, Australia; simply going to a warm place for your holiday).

Pest control How can we control pests like locusts? Poisons, not a good idea as they pollute the environment; introduce predators, like locust birds, but this may also upset the balance of nature; protection, eg covering plants with sheeting; prevent pests from breeding.

Writing You are living in a hot country and a plague of locusts descends on your farm. Complete the story “I was standing in the field when suddenly the sky darkened...”

Ted Wragg is professor of education at Exeter University