The caterpillar is all but invincible. It has bright warning colours that deter any birds which might want to eat it. It releases foul odours that deter hunters like beetle larvae, which rely more on scent. And it carries toxins that would make good on its threats. It’s a shame, then, that this caterpillar is dead. Its defences are the result of the creatures that killed it—an alliance between a parasitic worm and a glowing bacterium.

When the nematode worm Heterorhabditis bacteriophora burrows into an insect, it vomits out thousands of glowing bacteria, Photorhabdus luminescens. These release toxins that kill the insect and break its tissues into a nutritious soup, which the worms consume. The bacteria also make amino acids