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The Science of Self-Preservation: Chemical Defence in Plants

11 Feb 2020 | By Author Thornybush | Wildlife

During your South African safari with Thornybush, you’ll discover more amazing facts about survival than you ever would have imagined. They’re not all about the Big Five either.

While plants are hardly sentient beings, some of them know their stuff when it comes to beating off the bad guys. Some species have developed ways to make themselves pretty unappealing to would-be browsers and grazers, with chemically-based tactics to rival First World armies.

What are Chemical Defence Mechanisms?

A chemical defence mechanism is an inbuilt characteristic of a plant that is activated by a specific event such as touch or movement. When activated, these cells release chemicals that are either distasteful, harmful or poisonous to the offender.

For example, bitter almonds and apple pips both release hydrogen cyanide when crushed. This is extremely distasteful and can be lethal in large enough doses. Any animal or insect that bites into these items has no choice but to let go fast, and won’t try their luck again.

Chemical Warfare in the Bush

For other plants like the Tree Euphorbia it’s all fun and games until you get just below the surface. The sap inside this plant is so poisonous that the san bushmen use it to tip their arrows. This puts the tree euphorbia off the menu for any kind of browser, except the black rhino. Tree euphorbias are a favourite treat for these tough creatures and they are totally immune to the poison.

Other broad-leaf savanna plants take a less aggressive approach. The high concentration of tannin in their leaves make them distasteful to many insects and browsing animals.

For the wild potato plant, defence is the preferred means of attack. Several species of this plant can release compounds that mimic the aphid alarm pheromone. One whiff of this warning signal sends aphids scuttling for cover, far away from the plant.

Chemistry in Every Day Life

These kinds of insect-repelling tactics can be harnessed by organic gardeners to control pests without resorting to harmful chemicals. Marigolds and chrysanthemums are known for their insect-repellent properties which are used by vegetable gardeners worldwide to defend their crops.

Waging biological warfare on unwanted insects is a cheaper, safer and more environmentally friendly way to do things.

Ask your game ranger if they can point out any examples of plants that employ chemical defence mechanisms on your next game drive. They’re sure to know about a few more.

Get in touch to book your South African safari with Thornybush and get to learn more about the mysterious ways of the natural world.