Jellyfish-shaped robots made of magnetic ferrofluid can be controlled by light through an underwater obstacle course. Swarms of these soft robots could be useful for delivering chemicals throughout a liquid mixture or moving fluids through a lab-on-a-chip. Ferrofluid droplets are made of magnetic nanoparticles suspended in oil, and they can move across flat surfaces or change shape when coaxed in different directions by magnets. By immersing these droplets in water and exposing them to light, Mengmeng Sun at the Max Planck Institute for Intelligent Systems in Germany and his colleagues have now made them defy gravity. When ferrofluids absorb light – they are particularly good at that because they are dark – they heat up and any tiny bubbles within them expand.

A fleet of robotic jellyfish has been designed to monitor delicate ecosystems, including coral reefs. The underwater drones were invented by engineers at Florida Atlantic University and are driven by rings of hydraulic tentacles. The robots can squeeze through tight holes without causing damage. One expert praised the design but warned that the man-made jellyfish might be eaten by turtles. The flexible, 20cm-wide bots are modelled on the appearance of the moon jellyfish during its larval stage.