Apart from a shark alarm, nothing clears a beach more quickly than a swarm of blue bottles drifting inshore. Blue bottles are often found on exposed ocean beaches after strong onshore winds, they more uncommon in sheltered waters.
Blue bottles (Physalia utriculus) are not jellyfish; they belong to the phylum Cnidaria, which include corals and sea anemones. Another very similar species is the Portuguese Man-Of- War (Physalia physalia)
Blue bottles are not single animals; they are siphonophores or colonies, which consist of 4 different types of zooids, each with a specific role to play.
The float or pneumatatophone is a single individual, which provides the basic structure that supports the rest of the colony. The float measures 3 - 15 cm and is an aerodynamic, muscular, blue bag that secretes its own gas. It is able to sail by using muscles to control its curvature and the shape of its crest. The blue bottle floats on the surface of the ocean, but it can deflate and submerge briefly if necessary.
The gastrozooids are concerned with digestion. These digestive polyps respond to the presence of food by fastening on to it with their mouths. Their mouths cover the surface of the food by expanding up to ten times in size. The polyps secrete digestive enzymes over the food and these break down the fats, proteins and carbohydrates into simpler components
The dactylozooids are the fishing tentacles measuring 15cm to 10m, they detect prey, usually small fish and plankton, which are then enveloped and paralysed by the tentacles and conveyed to the gatrozooids. There is a single main retractable tentacle and also smaller, shorter tentacles which hang from under the float. The tentacles contain rows of nematocysts, these are tiny (0.001mm in diameter) but complex structures. Each nematocyst is a hollow capsule containing a hollow coiled thread, which is armed with barbs or spikes. The capsule also contains a neurotoxin composed of phenols and protein. The small opening of the capsule is covered by a hinged lid held down by a trigger. When the capsule is stimulated the nematocyst thread shoots out, latches onto the flesh of the victim with its barbs and then toxin is injected into the victim through the pores in the thread.
The gonozooids are concerned with reproduction. The blue bottle is a hermaphrodite so gonozooids contain both male and female parts. The fertilised egg develops into planktonic larval form of blue bottle. The larval form reproduces itself asexually by budding.
Blue bottles sting approximately 10 to 30000 people per annum on the eastern coast of Australia No fatality has ever been recorded.
If stung, use tweezers or a gloved hand to remove any tentacles stuck to the skin. Do not touch or rub the stinging site – this will only fire up more stinging cells. Irrigate the area with salt or fresh water (vinegar is no longer recommended), apply ice to control pain. If pain persists or other symptoms develop medical assistance should be sought.