by Jenny Edwards
There is nothing rare or endangered about bluebottles. They are about the most common animal we find washed ashore on our beaches and are relished by children who love to stomp on them.
Unfortunately it is not always possible for swimmers to avoid getting stung. If this happens pick off the tentacles and apply a cold pack and pain killers. Do not use vinegar.
Bluebottles (Physalia spp.) may not be everyone's favourite but they are worth a closer look. They are colonies. One individual swells up with gas and becomes the float. It is oriented at 45 degrees to the right or left of the rest of its colony and this means not all colonies will be blown ashore at once.
The underside of the float is an oval disc which secretes the gas, a slightly different composition in every bluebottle and different to the air. The oval disc also has a cavity which acts as a common stomach for all the other individuals in the colony.
The rest of the colony is made up of many groups of polyps suspended from the float. Each group has three polyps. One is a feeding polyp with a sucker-like mouth at the end furthest from the float.
Another is the fishing polyp. It is long and string-like with stinging cells that are triggered by touch, firing a barbed dart and poison into the small animals on which the colony preys. The fishing tentacles retract to deliver the catch to the feeding polyps which digest the food and share it with the colony.
The third polyp is branched with two types of branches. One type produces sperm and the other type eggs. A fertilized egg develops into a larval polyp which grows into a float for a new colony. Buds from it develop into all the other types of polyps.
Another common castaway on our beaches is the harmless (to us) by-the–wind-sailor (Velella velella, meaning little sail). It too is a colony, one of the most highly organized in the animal kingdom. Its disc-like float is chambered and has a sail above that, like bluebottles, is angled to right or left.
In the centre of the underside of the float is one large feeding polyp connected by a common "stomach" to the rest of the colony. Around the mouth are three rows of reproductive polyps and on the outer edge of the disc are three rows of short fishing tentacles. Velella can only catch very small prey, such as fish eggs, immediately below the surface and its poison is not toxic to humans.