An enormous mystery cloud has baffled US meteorologists this week who spotted the shape stretching over parts of Indiana, Ohio and Pennsylvania, but saw no rainfall.

The National Weather Service spotted the “conundrum”, and suggested it could be a swarm of “bugs”, however the altitude was so high, they were initially sceptical such a massive number of creatures could be flying so high.

NWS Wakefield said on Twitter: “No rain around the region with decent returns on radar. Usually we’d think we’re seeing bugs. Dual polarization radar products argue otherwise and some of these returns are above 10,000ft”.

The service added: “Migrating dragonflies is a possibility...they migrate in fall, usually prior to cooler weather arriving, and towards areas where more precipitation has fallen recently. That said, not sure DFs can fly that high or if they move in numbers great enough to produce these returns”

Another National Weather Service station in Cleveland also picked up the huge cloud and asked users on Twitter to guess what was causing it.

World's most endangered animals Show all 17 1 /17 World's most endangered animals World's most endangered animals Amur Leopard Endemic to the far east of Russia, the Amur Leopard has a population of around 84 and is critically endangered. Here follows every species that the WWF lists as critically endangered. Getty World's most endangered animals Sumatran Elephant The Sumatran elephant population now stands at only 2400-2800 Getty World's most endangered animals Yangtze Finless Porpoise Endemic to China's Yangtze River, the Yangtze finless porpoise has an estimated population of 1000-1800 Kenichi Nobusue World's most endangered animals South China Tiger When discovered in the 1950s, the South China tiger population was estimated to be 4000, by 1996 it was estimated to be only 30-80. Scientists consider the tiger to be "functionally extinct" as one has not been sighted for over 25 years World's most endangered animals Sumatran Orangutan The Sumatran orangutan was once found across the island of Sumatra and even further south on Java. Today it is found only in the island's north and its population stands at 14,613 Getty World's most endangered animals Western Lowland Gorilla Though it is the most populous of all gorilla subspecies, the western lowland gorilla is still critically endangered and its population has declined by 60% in the last quarter century Getty World's most endangered animals Sumatran Rhinoceros The Sumatran rhinoceros is the smallest of the surviving rhinoceros species. Only 80 are known to be living today. The last male Sumatran rhino in Malaysia died on 28 May 2019 Willem V Strien World's most endangered animals Sumatran Tiger There are fewer than 400 Sumatran tigers left today. They are severely threatened by deforestation and poaching Getty World's most endangered animals Eastern Lowland Gorilla Half of the rainforest of the Democratic Republic of Congo in which these gorillas live has been destroyed the past 50 years. There were 17,000 Eastern Lowland gorillas in the 1990s but scientists estimate their population has declined by over 50% since then Getty World's most endangered animals Vaquita The world's rarest marine animal has a population of only 30. They were discovered in 1958 and are endemic to Mexico's Gulf of California Paula Olson / NOAA World's most endangered animals Javan Rhino The most threatened of all rhino species, there are only an estimated 58-68 Javan rhinos left Reuters World's most endangered animals Saola The saola was first sighted in 1992, being the first large mammal to be discovered in over 50 years. Scientists have only sighted saola in the wild four times and it is considered critically endangered World's most endangered animals Malayan Tiger The Malayan Tiger population now stands at only 250-300 Getty World's most endangered animals Hawksbill Turtle The population of the Hawksbill Turtle has declined by more than 80% in the last century. They are threatened by black market poachers who kill them for their shell Getty World's most endangered animals Black Rhino The population of the black rhino dropped by 98% in the years 1960-1995 due to poaching, it stands today at around 5000 Getty World's most endangered animals Cross River Gorilla The population of the Cross River gorilla has been damaged by deforestation and poaching, it now stands at 200-300 Julie Langford World's most endangered animals Bornean Orangutan The population of the Bornean orangutan has been reduced by over 50% in the past 60 years, now standing at around 104,700. Their habitat has been reduced by at least 50% in the 21st century Getty

They later tweeted: “While we are not biological experts, we have determined (through input from our followers) that it’s most likely dragonflies mixed with other insects/birds!”

People on Twitter confirmed huge numbers of dragonflies were spotted in the region.

“I had so many in my yard. Felt like King Kong with all the planes around him,” wrote George Cheripko in reply to the NWS tweets.

“Definitely dragon flies,” said another person. “We have thousands flying around our yard and the field next to our yard.”

A common green darner dragonfly. The species is found from the northern US states down to Texas, Mexico and Panama. They are also found in the Caribbean, Tahiti, Japan and China (Getty)

Jason Dickhart added: “I saw a million dragonflies in my yard yesterday. Squirrels were going nuts.”

The species is reportedly the common green darner – named due to their resemblance to a darning needle. They fly south at the end of the summer, following their prey – mosquitoes and flies – to warmer climates in the southern states and central American countries.

Dragonflies were among the first winged creatures to evolve. Some enormous species emerged during the Paleozoic era, when oxygen levels were higher, with fossils recording individuals with wingspans of over two feet.