When water fleas detect certain predators lurking nearby, they grow tiny, sharp ridges below their heads called neckteeth. These predators—phantom midge larvae, also known as glassworms—are common in lakes worldwide. Now, scientists trying to learn how the neckteeth work have captured the first high-speed footage of a glassworm attack—and they have discovered that it is one of the fastest in the animal kingdom.
To document 48 attacks, the scientists each time placed three water fleas (Daphnia pulex) and a glassworm in an aquarium specially designed for high-speed filming. When a Daphnia meandered within reach, the glassworm ambushed it with long, jointed bristles that rapidly unfurl and contract (above) into a “catching basket.” The videos revealed how that capture works, showing the many bristles that prevent prey from escaping, including long upper lip hairs that fan out sideways during the attack. Other researchers had doubted these lip hairs could move, because they lack muscles. But they might be powered by the pressure of internal fluids.
The new videos also allowed the researchers to time the attack: The glassworm’s bristles reach the Daphnia in just 14 milliseconds on average, one of the fastest known strikes, they reported last week in PLOS ONE. (For comparison, the mantis shrimp attacks in just 4 to 8 milliseconds, and the record-holding trap-jaw ants and trap-jaw spiders take less than 1 millisecond.) After the glassworm catches the Daphnia in its basket, it needs just 43 more milliseconds to retract and start to swallow the prey.
The nature of Daphnia’s defenses remains a mystery. The neckteeth are likely interfering somehow with the action of the catching basket, the scientists say. Other experiments in more realistic conditions show that about 80% of Daphnia with neckteeth evade capture, compared with only half that lacked those defenses. For those that do not escape, though, at least the end is mercifully quick.