Fauna
Invertebrate

Sea Swallow

Glaucus atlanticus

Also known as Blue Dragon, Blue Sea Slug, Blue Angel, Glaucus

Sea swallows float upside down on the ocean surface, using a gas filled sac in their stomachs to stay afloat amidst pelagic winds and currents. Their dark blue underside faces upward toward the sky to blend in with the water, while their silvery backs face downward to camouflage against marine predators below. When feeding on colonial hydrozoans like the Portuguese man o' war, these tiny nudibranchs concentrate the prey's stinging cells into finger-like cerata to deploy as an intense defense.

PelagicVenomousColorful
Sea Swallow reference1 / 7
(c) Sylke Rohrlach, some rights reserved (CC BY-SA) · cc-by-sa
—observations
—countries
—peak records
Not EvaluatedConservation statusIUCN Red List categoriesLCNTVUENCREWEXNot Evaluated — not placed on the risk ladderRed List categories, explained →
Key facts
Diet & preyPortuguese Man o' War, By-the-Wind Sailor, Blue Button
Predators
  • Loggerhead Sea Turtle
ThreatsMarine pollution, oil spills, and ocean acidification
HabitatsPelagic open ocean surface waters
Life spanUp to 1 year
Classification
  1. OrderNudibranchia
  2. FamilyGlaucidae
  3. GenusGlaucus
  4. SpeciesGlaucus atlanticus
Range & activity
Range data is not available yet.
Safe observation
Interaction riskVery high
  1. Low
  2. Moderate
  3. High
  4. Very high
Why interaction risk is very high
Delivers a severe, painful sting by concentrating nematocysts from its prey; do not handle.
Why it is dangerous
Stores concentrated unfired stinging cells (nematocysts) from its hydrozoan prey, delivering a painful sting more potent than a Portuguese man o' war.
How to recognize a risky encounter
Look for a bright metallic blue and silver body with finger-like branching cerata floating upside down at the surface.
What to do
Never touch stranded or swimming specimens with bare hands; observe using a container or photograph from above without contact.
Responsible observation
  • Observe in water: Look for tiny blue and silver forms floating upside down near siphonophore colonies.
  • Never touch: Avoid handling stranded or swimming specimens because their concentrated sting is severe.
  • Check onshore winds: Search coastal beaches after strong offshore storms push surface life ashore.
Related species
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