Have you ever stared out over an estuary in winter? This stark, flat habitat is often heaving with birdlife. What’s the big attraction? What are they probing for? Well, lots of things, but worms are a popular treat and one in particular is worth a closer look: the estuary ragworm (Hediste diversicolor) is as beautiful as it is fascinating.
Popped in a tray of sea water, this odd, stringy creature immediately animates and transforms. The greenish sheen of its body gives way to the scarlet of the haemoglobin in its blood vessels, and a fringe of limbs shimmers in a rainbow of reflected colours.
How big is a ragworm?
Its head, thrashing left and right, sports four black eyes and six furtive, fleshy feelers that suggest the whiskers of a Chinese dragon puppet. A large worm might measure 12cm long and comprise over 200 segments, each with a pair of limbs called parapodia, which sport bristles, or setae.
Where do ragworms live?
Ragworms spend their lives in U- or J-shaped burrows in the rich estuarine mud, extracting nutrients from their surroundings in various ways. A pair of hard pincer-like jaws (paragnaths) are used to grab living prey and slice through carrion and plant material. When their burrows are submerged, the worms will reach out for edible morsels, sometimes even leaving their holes completely to hunt for food on the surface of the mud and under rocks.
What do ragworms eat?
They set traps too. A net of mucous is cast around the burrow entrance, which traps water rich in plankton and other organic material. The worm undulates its body and fans its parapodia, drawing a current of water down into its lair. It then rolls up this nutritious carpet of mucous and food and swallows the lot.
There is evidence that our humble worm is also a gardener – of sorts. Juvenile worms create an environment suitable for the growth of bacteria, which they can feast on without compromising their security. Larger worms, meanwhile, have been recorded collecting the inedible seeds of cord grass. They pull them into the mud before letting them germinate into a softer, more appetising meal. Evolved behaviour? Maybe. Or it could be simply a fortunate byproduct of a snatch and grab lifestyle.
How do ragworms reproduce?
Over the winter, the worms prepare for the finale of their lives. First, both sexes turn green, but a backdrop of white sperm in the male’s transparent body makes him appear brighter. The pigment is caused by the breakdown of their blood as they divert their energies to producing eggs and sperm.
Then the female signals her readiness to males with a ‘worm perfume’ wafted from her burrow entrance. The couple don’t meet, he simply releases his sperm outside her front door and she sucks it into her burrow. Spent, he then dies, but she has one last, bizarre, thing left to do. Her body ruptures, releasing thousands of fertilised eggs. Even then, she limps on, undulating her body to oxygenate the burrow until her larvae hatch and she eventually succumbs.
There ends a generation of humble ragworms – a surprise beneath the mud, quietly going about their business of turning scraps and invisible morsels into a meal for birds, fish and crustaceans.
So next time you find yourself at an estuary, look over the vast slick of smooth sediment before you and spare a thought for what lies beneath.
Main image © Peter David Scott/ The Art Agency
