It is dawn in a European forest, and gypsy moth caterpillars are looking for somewhere to hide. With early birds starting to rise, the caterpillars will spend the day in bark crevices or buried in soil. But one of them is behaving very strangely. While its peers head downwards, this one climbs upwards, to the very top of the highest leaves. It has come to die.

At the top of its plant, the caterpillar liquefies. Its body almost seems to melt. As it does, it releases millions of viruses, dripping them onto plants below and releasing them into the air. These viruses are the agents that compelled the caterpillar to climb, and eventually killed it. They are baculoviruses, and they