When it comes to self defence, if you don’t have fast feet, the next best thing is a chemical weapon. From venom to noxious smells to complex poisons, chemistry gives nature’s slowpokes a fighting chance for survival. And plants, rooted in the soil, are sitting at the bottom of the food chain. But, not all plants...

It was 401 BCE and Greek general Xenophon’s bad day was about to get a lot worse.

First, in 67 BCE they placed their toxic honeycombs in the path of the invading Roman army. This time they didn’t stand back and watch, but massacred the ‘drunken’ soldiers as soon as they were incapacitated.

A thousand years later, Olga of Kiev led her followers against the Russian occupation. But first, they provided the enemy army with several tons of mad honey – then slaughtered five thousand soldiers.

His Persian campaign had been a complete failure and he was on his way home with 10,000 hungry, demoralized soldiers in tow. They were crossing the Caucasus Mountains, prime rhododendron country, when the starving soldiers raided the local beehives, gorging themselves on the honey inside. It was a huge mistake: as he watched in horror, his soldiers first started to drool, then stumble around the fields disoriented and vomiting, finally collapsing, weak as kittens. As if they hadn’t been humiliated enough.

It’s called ‘Mad Honey’ and it’s produced by bees collecting the pollen of the rhododendron variety r. ponticum. It also became one of the world’s first bio weapons. Those Caucasian farmers applied the lesson they learned from the greedy Greek soldiers twice more.

The Russians then turned around and used the honey against a Tartar invasion: leading soldiers to an ‘abandoned’ camp where casks of mead, a drink of fermented honey, were consumed by the soldiers – with deadly results.

But, as chemistry is infinitely complex, so not all ‘mad honey’ is created equal. Long before it was used as a weapon of war, priestesses on the cliffs of Mount Parnassos drank a mead made from rhododendron honey before delivering their prophesies. The intoxicating effect of this particular honey was well known to barkeepers for centuries. Both English and Scottish tavern owners imported it to give their brew an extra kick. Happy patrons knocked it back well into the 18th century.

Plants may be trapped by their roots, but chemistry gives them a fighting chance in the struggle to survive. Rhododendrons’ unique biology makes them members of a very special club: plants that have changed the course of human history.