By-the-wind sailor (Velella velella)

What are they?

By-the-wind sailors, unusually, are also recognized throughout the world by their scientific name, Velella velella. They are tiny blue-coloured relatives of the Portuguese man-of-war (Physalia physalia), but instead of the float having a bladder, it has a flat disc with a diagonal sail. Like the Portuguese man-of-war, each ‘individual’ is composed of groups of polyps, specialised for feeding, breeding and catching prey.

By-the-wind sailor (Velella velella) floating in a pool
Photograph by Malcom Lee

Why are they called By-the-wind-sailors?

The sail gives the animal both its scientific (i.e. from velum, a sail) and its common name, 'by-the-wind-sailor'. They exist in two forms, either left - or right - handed. The wind tends to distribute them into groups, depending whether they are either left - or right - handed, so strandings tend to be made up of one group.

What is their life-history?

Remains of a By-the-wind sailor (Velella velella)
Godrevy 28th Sept 2004
Photograph by David Williams

Where do they normally live?

On the surface of warm seas world-wide.

What do they feed on?

Creatures in the plankton, relative to their size.

What feeds on them?

Sea slug (Fiona pinnata), sunfish (Mola mola) and violet sea snail (Janthina janthina) are probably their main predators.

Do they sting?

They do have very low stinging ‘batteries’ sufficient to help them capture their prey. At most, humans would feel only a tingle if they had sensitive skin, or handled them in large numbers.

What size are they?

Up to 10 centimetres.

Has this species become commoner in the past few decades?

In the 19th century this species was considered to be rare. Presumably the warmer sea temperatures have enabled by-the-wind sailors to flourish and breed further north than the Bay of Biscay. Flotillas occur throughout the warmer seas of the world, blown hither and thither by the vagaries of the wind. Onshore winds blowing continuously over a period always pose the threat of a wreck. On the British and Irish coasts, it is the dominant westerlies combined with the North Atlantic Drift that directs them up into the Celtic Sea/Irish Sea much more abundantly than the English Channel.

A solitary By-the-wind sailor (Velella velella) in the sand
Photograph by Malcom Lee

Research ideas

• report the proportion of left-sailing (north west) to right-sailing (south-west) animals. The left –hand ‘sailors’ should be much commoner. Take careful note of the beach, its aspect and the wind direction of the last few days.
• report the largest and smallest that you can find on any one beach.
• report any ‘fellow travellers‘ e.g. Portuguese man-of war, (one has been reported this year); violet sea snails that feed on by-the-wind sailors; buoy barnacles (Lepas fascicularis), a goose barnacle that forms its own float; and of which many have been found this year.

Stella Turk

Classification:

By-the-wind sailors are members of the Cnidaria (stinging animals) in the sub-group Hydrozoa (hydroids, Portuguese man-of-war etc). The other main sub-groups in the Cnidaria are the Scyphozoa (jellyfish) and Anththozoa (sea anemones and corals).

Other items that may be of interest:

• Marine Strandings in Cornwall
• Marine sightings in Cornwall
• Marine Conservation in Cornwall