The navies of the Byzantine Empire used Greek fire, a blazing concoction possibly of petroleum and phosphorus, to incinerate their opponents, and Renaissance tyrants despatched their foes with a range of poisons. But over the centuries mankind has made only limited use of chemical weapons - lat least until the release of mustard, chlorine and phosgene gases over the trenches in the First World War. But the animal world has for thousands of years had the ability to call upon a vast arsenal of gases, poisons, syringes, fluids, burning essences and appalling smells. The bombardier beetle, when provoked, fires a caustic cocktail at its attacker. It does so by means of a swivelling 'gun turret' in its abdomen that throws out 50 jets of irritant vapour, each with an explosive click, and at boiling point. Explosions and vapour are created in a thick-walled chamber in the abdomen. Darkling beetles squirt a foul-smelling liquid from their abdomens; but they are not as quick on the draw as the bombardier beetle and often get eaten before they can open fire. Lubber grasshoppers, when alarmed, ooze phenol and quinones, both insect repellents, and whip scorpions emit an acid vapour akin to gear gas. Giant millipedes have made an even more effective adaptation by spraying cyanide from pores along the sides of their bodies. Swallowtail caterpillars have the ability to exude a repellent smell if attacked; they carry this defence into their adult form and, when a number of swallowtail butterflies are together, in times of danger they can put out a powerful chemical miasma to protect the group.