Invertebrates
Bobbit Worm
Eunice aphroditois · also called bobbit worm, sand striker
The bobbit worm is a predator that hides almost its entire body in the seafloor, leaving only its antennae and jaws above the sand. When a fish brushes past, it strikes upward fast enough to cut prey in half, then drags the pieces underground. Buried individuals can exceed three metres.
Overview
Bobbit worms live on sandy and gravelly seabeds of tropical and warm-temperate oceans worldwide. Commonly about 1 m but recorded over 3 m buried, they are iridescent, many-segmented worms that ambush fish and invertebrates from a burrow.
A strike that slices
Waiting buried with only its antennae and jaws exposed, it strikes upward so fast and hard that prey is sometimes cut cleanly in two, then dragged down into the burrow.
Hidden for life
It spends nearly its whole life inside a mucus-lined burrow, extending only a few centimetres to hunt — which is why its true length so often surprises divers.
Status
The bobbit worm is Not Evaluated, widespread across warm seas with no known specific threats.
Bobbit Worm: common questions
How does the bobbit worm catch its prey?
It is a pure ambush predator that spends its life buried in the seabed inside a burrow, with only the front tip of its body, carrying five sensitive antennae and its jaws, protruding above the sediment surface. When a fish or other prey animal swims close enough to brush against the antennae, the worm launches an extremely rapid upward strike, seizing the prey with its curved, blade-like jaws, and in the most forceful strikes the prey can be sliced partly or entirely in two. The worm then drags whatever it has caught down into its burrow to feed, safe from other predators and out of sight.
How big can a bobbit worm actually get?
Because they spend nearly their entire lives buried, with only a few centimetres of body exposed, the full size of a bobbit worm is rarely apparent until one is deliberately excavated. Commonly encountered individuals are around a metre long, but specimens well over three metres in length have been recorded when dug out completely, despite the body being only about 2.5 centimetres wide, giving large individuals an extraordinarily long, ribbon-like proportion. Their hidden lifestyle means many divers who have seen only the exposed hunting tip of a bobbit worm are surprised to learn how long the rest of the animal is.
Is the bobbit worm dangerous to humans?
It is not considered dangerous to people in any serious way, since it is an ambush predator adapted to catching fish-sized prey rather than defending itself against large animals, and it has no interest in anything as big as a human. However, its jaws are genuinely sharp and powerful for their size, and there are anecdotal reports from aquarium keepers of painful bites when a hand was placed near a hidden worm, so divers and aquarists who encounter one are generally advised to look but not touch. Some accounts also mention that its bristles can cause skin irritation on contact.
How did the bobbit worm get into home aquariums?
Bobbit worms and their relatives sometimes arrive unnoticed as tiny juveniles hidden inside pieces of live rock, the natural reef rock used to seed and populate marine aquariums, and can then grow for months or years concealed within the aquarium's rockwork before being discovered. Aquarium owners frequently only realise they have one when fish and other tank inhabitants begin disappearing overnight with no obvious cause, and locating and removing a well-established bobbit worm from a reef tank can be a difficult and destructive process because the animal retreats deep into the rock and burrow structure when disturbed.