For more than 420 million years, plants, insects and their predators have co-evolved based on a chemical arms race including deployment of refined chemical defence systems by each player. Cyanogenic glucosides are produced by numerous plants and by some specialized insects and serve an important role as defence compounds in these intimate interactions. Burnet moth larvae are able to sequester cyanogenic glucosides from their food plant as well as to carry out de novo biosynthesis. Here we show that three genes (CYP405A2, CYP332A3 and UGT33A1) encode the entire biosynthetic pathway of cyanogenic glucosides in the Burnet moth Zygaena filipendulae. In both plants and insects, convergent evolution has led to two multifunctional P450 enzymes each catalysing unusual reactions and a glucosyl-transferase acting in sequence to catalyse cyanogenic glucoside formation. Thus, plants and insects have independently found a way to package a cyanide time bomb to fend off herbivores and predators.