Bomber worm

(Swima spp.)

When danger approaches, it’s bombs away for this worm.

The midnight zone is a world of total darkness where predators lurk in the shadows ready to pounce on prey. The small bomber worm (Swima spp.) swims in the waters a few meters above the seafloor. A wriggling worm is exposed out in the open, but it has a secret weapon to avoid becoming a meal for a hungry predator. 

A bomber worm has eight sacs of bioluminescent fluid just behind its head. When disturbed, it releases a “bomb” that bursts with a green glow. While this light show distracts the predator, the little worm makes a quick escape and paddles to safety. Safe from harm, it regenerates its lost bombs so it’s ready to face its next threat.

MBARI researchers and their colleagues first discovered the green bomber worm (Swima bombiviridis) in 2009 and described a second species—the shining bomber worm (Swima fulgida)—two years later. While they’re relatively recent discoveries, these bomber worms aren’t rare, they just live at extreme depths below 2,700 meters (8,900 feet). These remarkable, but elusive, worms underscore how much we have yet to learn about the midnight zone.

Fast Facts

Maximum size: 30 millimeters (about 1 inch)

Depth: 2,700–3,600 meters (8,900–11,800 feet)

Habitat: benthopelagic, occurring in the waters just above the seafloor

Range: northeastern Pacific Ocean

Diet: unknown

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Research publications

Osborn, K.J., S.H.D. Haddock, F. Pleijel, L.P. Madin, and G.W. Rouse (2009). Deep-sea, swimming worms with luminescent “bombs.” Science, 325: 964. dx.doi.org/10.1126/science.1172488.

Osborn, K.J., S.H.D. Haddock, and G.W. Rouse (2011). Swima (Annelida, Acrocirridae), holopelagic worms from the deep Pacific. Zoological Journal of the Linnean Society, 163: 663-678. dx.doi.org/10.1111/j.1096-3642.2011.00727.x.

Osborn, K.J. and G.W. Rouse (2010). Phylogenetics of Acrocirridae and Flabelligeridae (Cirratuliformia, Annelida). Zoologica Scripta, 40: 204-219. doi.org/10.1111/j.1463-6409.2010.00460.x.

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