US embassy in Cuba
© AFP / Yamil LageThe US embassy in Cuba, where mysterious ‘attacks’ on US embassy staff were reported.
Just two years ago, the U.S. Embassy in Havana was bustling with U.S. personnel sent by the Obama Administration to restore diplomatic relations with Cuba. Today it is nearly empty. In late 2016, diplomats started hearing a loud, piercing noise. Two dozen of them reported symptoms such as ear pain and dizziness, and were diagnosed with injuries consistent with a concussion. Suspicions of politically motivated "sonic attacks" soon followed. The U.S. State Department recalled most personnel from Cuba and reduced its embassy staff in Havana to a skeleton crew. Cooperative measures between the two governments stalled amidst conspiracy theories of high-tech attack. Despite ongoing investigations by American and Cuban government agencies, and extensive coverage of the study by major news outlets, the source of the strange noise provoking the crisis has remained an enigma.

But a new study indicates that the culprit behind this debacle is in fact... a cricket. According to Alexander Stubbs, a scientist in the Department of Integrative Biology and Museum of Vertebrate Zoology at the University of California, Berkeley, the mysterious noise is actually the echoing call of the Indies short-tailed cricket (Anurogryllus celerinictus). Stubbs will present his findings this week at the 2019 Annual Meeting of the Society for Integrative and Comparative Biology in Tampa, Florida, based on a paper that was just released through the bioArxive online database.

The suspicious noise had been recorded by U.S. personnel stationed in Cuba. One of these recordings was released to the public through the Associated Press (AP). Stubbs listened to the recording and was reminded of insect calls that he had heard while doing field work in the Caribbean. He decided to investigate further, reasoning that if an insect were responsible for the noise, it should be possible to identify the particular species based on the unique acoustic signature of its call.

Stubbs analyzed the acoustic power of the mysterious noise as a function of frequency. Using publicly available field recordings, Stubbs did the same analyses for hundreds of insects and found a few potential matches. But the nuances of the pulse structure in the AP recording did not perfectly match any of the insect recordings made in the field.

Then Stubbs realized that the U.S. diplomats may have made the recordings indoors, with the pulses of sound echoing off the walls. To mimic these conditions, Stubbs played the insect calls on indoor speakers, recorded the echoing calls, and performed the analyses again. The new results were noticeably different. Stubbs found that the echoing call of the Indies short-tailed cricket (A. celerinictus) was a near perfect match to the AP recording in pulse structure. Further tests in collaboration with bioacoustics expert Fernando Montealegre-Z at the University of Lincoln (UK) showed that the characteristic frequency decay within each pulse is consistent with the biomechanics of this cricket's sound production.

The possibility of an insect causing the strange noise had actually been proposed previously. A group of Cuban officials submitted a report to the U.S. government in 2018 suggesting that the noise came from the Jamaican field cricket (Gryllus assimilis). But the report was perhaps disregarded by U.S. officials because the short chirp of the Jamaican field cricket does not match the grating, continuous sound in the diplomats' recording from Cuba. The cricket species suspected by Stubbs and Montealegre-Z, in contrast, has a continuous call that precisely matches the echoing sound in the AP recording.

Why was the Indies short-tailed cricket not implicated before? A. celerinictus has only been documented in Jamaica and Grand Cayman and is not known to occur in Cuba. But it's possible that this cricket was actually in Cuba all along. A. celerinictus used to go by a different name: A. muticus, another species that is nearly identical, and that does occur in Cuba. An entomologist at the University of Florida, Thomas J. Walker, distinguished the two species from each other in 1973 based on the frequencies of their wing strokes. But the distinct geographic ranges of the two crickets went unnoticed for over 40 years - until Stubbs used Walker's field recordings of the crickets, which Walker had made available on his website, to investigate the strange recording from Havana. It is possible that the Cubans actually found the organism responsible but simply mis-identified it.

These findings add fresh intrigue to an ongoing and heated political controversy. Some factions still blame a hypothetical "sonic weapon" for the jarring noise, whereas others have suggested microwave- or ultrasound-based devices. Meanwhile, several medical professionals have questioned the methods used to diagnose the afflicted U.S. personnel, raising the possibility that some or all of the reported symptoms could have been psychogenic rather than physically manifested from hearing the noise. These new findings may promote deeper investigation into the possibility that the shrill sounds that emptied the U.S. Embassy in Cuba resulted from cricket calls. Regardless of the outcome, this study demonstrates the practical importance of organismal biology research and open source scientific data.