The US National Weather Service released a report last week about a mysterious butterfly-shaped cloud sported over St. Louis. This discovery was made on the afternoon of Friday, Sept. 19. According to the report, the strange incident demonstrated a swarm of migrating monarch butterflies resembling a butterfly on radar. The monarchs are always said to fly between 1,525 meters to 1,825 meters (5,000 feet and 6,000 feet) above the ground.

When sighted, the clouds were small with fluttering wings and were headed towards the South of Mexico. Even though, no one saw the butterflies, the radar signals asserted that the ‘targets’ were flapping, flat and biological similar to the monarchs. This is unique compared to the ordinary hummingbirds that prefer travelling at treetop level. The height of the sighting also ruled out the Hitchcock-like situation.


Many similar scenarios have been witnessed in the past. For instance, in 2011, a strange radar image that resembled a startled flock of birds occurred in Arkansas and Beebe. This looked like a bird’s head and beak. In June 2003, radar image that baffled forecasters in Alabama and Huntsville turned out to be reflective particles used to test military radar. The butterflies-blob’s timing matches the recent monarch exodus from the Great Lakes region as reported by the nonprofit organization Monarch Watch.

Many scientists believe that the monarchs may have gathered due to favorable weather condition. The monarchs normally take advantage of the air currents to soar like birds, thus minimizing their energy loss during their two-month trip to Mexico. In some occasions, the butterflies fly in ones or twos, but swarms of dozens or hundreds of spectacular orange-winged insects have been sighted by researchers tracking their migration.

Must Read: Migrating Monarch butterflies formed butterfly shaped radar blob, report says

The National Weather Service said it believed that, despite the small size of mysterious butterflies, their fluttering wings are good radar targets. The changing of weather patterns and other ecosystem factors such as cold temperatures, exposure to drought and the pesticides along the migration routes may cause decline in monarch population.

Must Read: Migrating Monarch butterflies formed butterfly shaped radar blob, report says

In Mexico, the forests can at times contribute to the decline in monarch migration. The figures keep changing and can sometimes hit a record of below 33 million butterflies overwintering in Mexico as witnessed by the forecasters this year. The unique discovery has attracted many scientists and nature lovers who are keen to monitor the progress of the discovery and its significance.