If you think that plants are real pushovers, incapable of defending themselves against their enemies, you couldn’t be further from the truth. Plants are no wimps! Though they do not have strong teeth to tear predators apart, or speed to escape from their enemies, they do possess effective weapons to protect themselves and even their neighbours.

Since plants are unable to escape from those who feed on them, they have to rely on other means to defend themselves. In general, plants have two main defence mechanisms – poison and armour.

Intruders, Beware!
When an intruder or enemy is detected, plants send out very clear distress signals to protect themselves and even their neighbours.

Recent research by scientists from Kyoto University in Japan found out that the Lima bean plant emits chemicals to warn all its neighbours of danger. This is the signal for all the plants to get their defences ready and operational.

When an antelope or other large animals chew on the leaves of the African acacia tree, the tree may issue a warning to its neighbours. How does it do this? First, the tree pumps nasty chemicals into its leaves to make them taste bad. Then, it may send out a special gas through its leaves to warn its neighbours of danger. As this gas drifts to other acacia trees, it “tells” those trees that a hungry animal is on the prowl. Then the trees will begin to pump the nasty chemicals into their leaves. Soon, the antelope will find the leaves of the first tree too yucky to eat. It moves on to the next tree and the next but all of the trees taste equally yucky. The antelope may have to wander more than 45 metres away to find a tasty meal!

The sweet potato kills its enemy softly. The plant possesses a trypsin inhibitor which prevents the insect that is feeding on it from absorbing the proteins from the plant. Without the proteins, the insect will not be able to develop properly and may never be able to reproduce. Eventually, the insect will die. Tricky!

Other plants such as chillies, spices and herbs produce chemicals that give the leaves and stem a strong taste or smell. These substances either discourage or even kill insects and other animals that try to eat the plants.

A Thorny Issue
Some plants do not possess poison or chemicals to protect themselves, but they have other prickly ways of fighting back.

For instance, thistles, roses and many other plants are covered with sharp thorns. When an animal tries to bite them, you can imagine how much it hurts!

In the Galapagos Islands, cacti grow thick stalks of more than two metres tall, putting the tender leaves well out of the reach of giant tortoises.

Nettles deliver stinging blows to those who dare to try and eat them. They have tiny hairs covered with chemicals that can inflict pain. The hairs work like needles. If an animal tries to eat it, the hairs give the animal’s mouth an “injection” of those chemicals. Ouch!

Survival of the Fittest
Plants “care” for their neighbours as the Lima bean plant and African acacia tree show, but they may also fight amongst themselves for survival. For example, radishes produce a chemical substance which slows the growth of spinach. Similarly, walnut and apple trees cannot grow together because chemicals released from the walnut tree will kill the apple tree.

Now, do you still think plants are weak and defenceless? In fact, they are a lot tougher than we think.