Deadly Portuguese man o’ war jellyfish, with tentacles as long as five London buses. People have been reporting these sightings all around the English coastline, prompting fears of invasion among conservationists. Normally living far from land in the ocean, experts from the Marine Conservation Society (MCS) say that the Society’s survey team has received many reports of them near the shoreline this year.

The venomous jellyfish, which can reach 160 feet in length and can be deadly. Even with their massive sive, swimmers and surfers are not always able to spot them before they are stung. And a single touch from this massive monsters can be deadly.

Last month, there were 30 reports from locals in the southern English counties of Devon and Cornwall of the aptly names barrel jellyfish drifting near the coast. Experts are saying that data suggests that a significant recent rise in the numbers of some jellyfish species in UK seas is underway.

But why is this happening? Some suggest global warming is to blame. Researchers have so far been baffled. In 2013 there were 1,000 reports involving hundreds of thousands of jellyfish in England. Last year the number of reports increased again to over 1,400 reports, and by July this year the survey had already recorded over 1,000 reports. August is usually a peak month for jellyfish sightings and so 2015 looks to be another record breaker.

The creature’s venomous tentacles can deliver a painful sting, similar to a cut with a knife, with rash-like symptoms developing immediately. However, the pain depends on the level of exposure.

The Marine Conservation Society said the rise in the number of jellyfish around the British coast can “no longer be ignored.”