[2][3] Examination of the contents of the gut shows that Hediste diversicolor is a predator and generalist scavenger, able to adapt its diet to whatever is currently available.

It spins a mucus net at the entrance of its burrow in which it traps phytoplankton, zooplankton, diatoms, bacteria and other small particles.

When the availability of suitably-sized food particles is low it emerges from its burrow and hunts for small invertebrates, seizing them with its strong jaws.

[5] They also draw, otherwise not edible, cordgrass seeds into their burrows and let them sprout to produce high-quality food, one of the rare examples of “gardening” by animals.

At the same time, the females turn a duller dark green on the dorsal surface with their earlier orange-brown pigmentation still showing through.

[2] Synchronized spawning takes place in early spring, usually at the time of the new or full moon when the water has warmed up after the winter and attained a temperature above 6 °C (43 °F).

When tests were undertaken in southern England on establishing the seagrass Zostera noltei, it was found that efforts were more successful when the ragworm was excluded from the area of transplanted material.

In another planting trial, the pioneering cordgrass Spartina anglica, used to prevent coastal erosion, was similarly adversely affected.

It has also been used to evaluate the quality of marine sediment because it bioaccumulates certain heavy metals such as lead, cadmium, chromium and arsenic.