Quantum dots – fluorescent nanocrystals – have a range of applications but they are not always easy to make. Now, Mark Green of King’s College, London, and colleagues have found an environmentally friendly way of making biocompatible cadmium telluride (CdTe) quantum dots. They spiked the ground where earthworms (Lumricus rubellus) lived with cadmium chloride and sodium telluride. Eleven days later, they were able to recover green fluorescent CdTe quantum dots from the guts of the worms. As a bonus, the dots came out coated with a passivating layer that makes them water-soluble. In addition to being a fabrication technique, understanding the biology and biochemistry involved could help in heavy-metal remediation