Plants that kill can often cure (plus exercise)

Plants are chemical factories. From simple starting points of water, carbon dioxide, oxygen, nitrates, a few trace elements and many enzymes, they can manufacture intricate chemical compounds.

Some of these chemicals are produced to protect the plant from grazing animals or other plants that may try to grow too near and compete for light or nutrients. If the plant does not have a physical way of protecting itself - by spines, hairs or thick coverings, for example - it is very likely to have survived by its chemical wits.

Here are examples of how plant poisons foil pests:

* Tomatoes and potatoes make a chemical that prevents creatures from digesting their food, and these pests starve to death.

* The wild potato pretends to be a frightened aphid by producing a chemical these insects use to signal fear to one another. Believing fellow aphids are in danger, these pests run away.

* Chemicals called limonoids, produced by citrus fruit, may taste bitter to us, but they kill or stunt the growth of insect pests.

* Members of the carrot family produce a sneaky poison. A pest chewing leaves in the shade of the plant is safe. But once out in the sun, the chemical changes into a deadly poison.

Aspirin, quinine, opium, curare and hundreds of other drugs have evolved in plants as chemical weapons against pests. The drugs work because they change the body’s chemistry. When a small creature - say, a beetle - eats a meal containing a drug, the animal may get a big enough dose to drive it mad, make it ill, prevent it from having babies, even kill it. As we are so much larger than a plant’s intended victim, if we take a beetle-size dose, our body chemistry changes but not so drastically.

Medicines are derived from chemicals that form plants’ chemical warfare. So medicines are by nature poisons. While drugs can be useful in treating disease and in surgery, these same chemicals may be harmful - even deadly - to humans in large doses.

Exercise

Look closely at an orange skin. Each dot on its surface holds a droplet of oil inside. That oil, when released, smells delicious to us, but it is deadly to insects.

Sniff the orange. Then, break the skin with your fingernail as Sniff the orange. Then, break the skin with your fingernail as if you were an insect trying to get into the fruit. Sniff again.

Grate the whole surface of an orange, and put the grated skin into a bottle. A lot of oil is released, and this can kill flies and many other insects within two hours.

Rub grated orange skin into your dog’s fur to kill its fleas. The dog will smell “grate” too!