The mauve stingers, which invade Maltese waters every summer, are back, much to the dismay of swimmers who had gloated over the absence of these jellyfish over the past two months.

Abnormally large mauve stingers have been spotted floating in thick groups in various localities across the island, including Ċirkewwa and Żurrieq.

In some cases, the bell diameter of these jellyfish exceeded 10 centimetres. This means they were mature species seeking shallow depths to reproduce before dying.

Environmentalist Alan Deidun said the mauve stinger – pelagia noctiluca – usually sought shallow depths across the Mediterranean in December and January.

These jellyfish need to float up towards warmer waters to be able to reproduce and, most probably, bad weather and rough seas hindered the yearly cycle.

Once the sea calmed down, they scurried towards the surface to reproduce. The offspring will transform into a medusa – and, therefore, become dangerous for swimmers – in six weeks.

The mauve stinger started increasing in numbers in the early 1980s and gained dominance over the years until it “out-competed” the other species.

Although it inflicts a nasty painful sting, hospitalisation is rarely needed if a person is attacked. Those who end up in hospital are usually people who suffer from allergic reactions.

Sightings can be reported to the Spot the Jellyfish team on www.ioikids.net/jellyfish or ioi-moc@um.edu.mt or by phoning 7922 2278.

The mauve stinger. Photo: Daniel Jones