Diplomats from the US and Canada in Cuba complained of bizarre symptoms in 2016. Some said the condition started after they heard a strange noise.

This prompted speculation about potential "sonic weapons ." The US eventually cut its Cuban embassy staff by 60%.

But a team of zoologists and biologists has concluded that the sound diplomats and their families heard is very similar to that of an Indes short-tailed cricket.

The new finding is the latest in a string of conflicting hypotheses about what might have happened in Cuba.

Forget rogue sonic attackers or microwave weapons — blame the crickets.

That's the conclusion of a group of scientists who performed a new analysis of the sounds that 24 US diplomats and their families stationed in Cuba reportedly heard in late 2016.

The noise in question — which only some of the affected American and Canadian diplomats reported hearing — was thought to be connected to physical symptoms they experienced, including hearing loss, speech problems, balance issues, nervous-system damage, headaches, ringing in the ears, nausea, and even some signs of mild traumatic brain injury.

That led to speculation about a "sonic attack" from some unknown weapon. Previous studies of the sounds suggested there might be a mysterious and dangerous brain-injuring force at work. Others mentioned the possibility that the chirps were produced by weapons that use microwave radiation.

But the new analysis suggests that, based on the recording of the noise released by the Associated Press (AP), the sound was likely nothing more than a cricket.

"The calling song of the Indies short-tailed cricket (Anurogryllus celerinictus) matches, in nuanced detail, the AP recording in duration, pulse repetition rate, power spectrum, pulse rate stability, and oscillations per pulse," insect researchers wrote in a scientific paper currently under review, published online as a preprint in bioRxiv on January 4.

Though the recording the AP released isn't exactly like the sounds bug-watchers hear in the field, the scientists think that the sound of crickets, when recorded indoors as it ricochets off walls, floors, and ceilings, is the culprit. To verify this, the scientists played an A. celerinictus field recording "on a high-fidelity loudspeaker" indoors. When they did, the pulse structures of the two recordings matched up almost perfectly.

"All I can say fairly definitively is that the AP-released recording is of a cricket, and we think we know what species it is," lead study author Alexander Stubbs from the University of California, Berkeley told The New York Times.

The authors noted, however, that "the fact that the sound on the recording was produced by a Caribbean cricket does not rule out the possibility that embassy personnel were victims of another form of attack."

Reports of mysterious chirping sounds

In their reports about the experience, some diplomats said the noise they heard was like a "loud ringing or a high-pitch chirping, similar to crickets."

The first person who came forward in Cuba complaining of health issues said that the noise he heard stopped abruptly when he opened his front door. Others said the sound stopped when they moved to a different area in the house. These changes could be related to the way crickets hush up if they sense danger.

Other reports about the bizarre sounds suggested that they waxed and waned with the seasons. (A cricket's chirping tends to get louder and faster as temperatures rise.) What's more, many diplomats complained they heard the sounds at night, which is a cricket's favorite singing time.

Adult domestic crickets. Visarut Sankham/picture alliance via Getty Images

The idea that the sounds could come from crickets wasn't new. One Cuban government report had previously suggested that a Jamaican field cricket might be responsible for the sound. But the scientists behind this new report say the Jamaican cricket call "would sound qualitatively different, even to non-experts," since the Jamaican cricket's chirp isn't continuous.

"It is understandable that US authorities met this explanation with skepticism," the scientists wrote in their report.

Diplomatic consequences

Not all the diplomats in Cuba described the same sound, however. One diplomat reported a "blaring, grinding noise" that woke him up, according to the AP, while others said they could walk "in" and "out" of loud noises that were audible only in specific spots. Some said they didn't remember seeing or hearing anything out of the ordinary at all before their symptoms started.

The US State Department eventually determined that the incidents were "specific attacks" and cut its Cuban embassy staff by 60%, despite Cuba's fervent denials of wrongdoing.

"Cuba has never, nor would it ever, allow that the Cuban territory be used for any action against accredited diplomatic agents or their families, without exception," the Cuban government previously said in a statement.

The US government also commissioned a team of researchers from the University of Pennsylvania's Center for Brain Injury and Repair to evaluate 21 of the patients who'd been in Cuba. The findings, published in March 2018, suggested that three months after the experience, 81% of people still had cognitive issues, 71% had balance problems, 86% had vision issues, and about 70% still reported hearing problems and headaches. Several doctors pointed out major flaws in that study, however.

A few months later, several US embassy workers in Guangzhou, China were diagnosed with similar brain injuries after reportedly hearing mysterious sounds, and at least nine were evacuated, according to a July 2018 report from the Wall Street Journal. (The cricket hypothesis doesn't immediately explain why diplomats in China reported eerily similar symptoms.)

The cricket is an incessant, ceaseless insect

Although many questions linger about why dozens of diplomats reported strange symptoms and where they came from, what's not in dispute is that the calls of short-tailed crickets can be nasty buzzing, ringing sounds to hear. The songs of A. muticus, which chirps around the Dominican Republic, were described by scientist H.A. Allard in 1957 as "powerful, penetrating, buzzing, almost ringing noises."

That short-tailed male's wing-rubbing creates, "a continuous ringing z-z-z-z-z-z- of tremendous volume and penetration which practically fills a room," he said.

(In case you were wondering, nature's loudest recorded insect is not a cricket, it's the North American Tibicen walkeri cicada.)

Here's the AP's original recording of the sound heard in Cuba:

As the bug researchers note, this isn't the first time we've confused nature's oddities for a human menace. A "yellow rain" that descended from the skies after the Vietnam War, for example, was at first thought to be a chemical weapon from the Soviet Union. But it turned out to be Southeast Asian honey bee poop falling from above.

Correction: A previous version of this story mistakenly referred to the Caribbean short-tailed cricket as the loudest North American insect. The North American Tibicen walkeri cicada is the loudest.