Cave creatures found in the Amazon are unable to make sounds.See unique new species

Whether for an awkward silence or on a quiet summer night, there is one animal that can be counted on to fill the void with noise: crickets.

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The notoriously loud insects rub parts of their body together to create the well-known chirp, chirp, chirp.

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However, in a cave deep in the Amazon rainforest, one species of cricket hops around in the dark in complete silence.

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Called Zebragryllus aphonus, the surprisingly discreet cricket was recently discovered as a new species in Cana dos Carajs, in northern Brazil, according to an April 24 study published in the European Journal of Taxonomy.

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The dark brown insect has small stripes running the length of its body and legs, confirming its place in the Zebragryllus genus, named for the zebra patterns found on the species, according to the study.

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Before this find, all known species of Zebragryllus were known to have stridulatory apparatus on the tegmina, or hind wing, of males, researchers said.

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Stridulatory apparatus are a series of ridges on the wings of the crickets that can be rubbed together to create sound, according to Advances in Insect Physiology. They play a crucial role in crickets reproductive behaviors.

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But when researchers examined the species found in the cave more closely, they saw it was missing these ridges, meaning the crickets would be incapable of producing sound, according to the study.

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The unique feature was matched with a lack of development of the tympana, or internal membrane of the ear, researchers said.

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These two characteristics may be adaptations to the caves in which they were found, researchers said.

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The silent crickets were found in both leaf litter and caves, suggesting researchers caught adaptation in action.

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The crickets were found foraging in the leaves during the night, then staying in the caves during the day, according to the study, giving researchers two possible reasons for their silent lifestyle.

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Animals of all kinds change physically when they move to a cave-dwelling life, according to the study, so the lack of sound-making ridges and hearing may be a complete adaptation for some of the crickets life spent in caves.

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Or, the cricket may be moving from a life spent primarily outside to one protected by the rocky holes, meaning the adaptation is the beginning of a morphological change in the species until it becomes entirely cave-dwelling, according to the study.

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Whether deep in caves or compressed under leaf litter and soil, the environment is dense, making it more difficult for sound to travel from one cricket to another.

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However, we still lack sufficient evidence, and the caves where this species was found are not extensively developed, often less than 10 meters in length, researchers said. Thus, only evolutionary studies and descriptions of yet-unknown species within this genus will provide a better understanding of these findings and validate some of these hypotheses.

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Researchers also described a second newly discovered species in the study, Zebragryllus mebengokre, which had the sound-making ridges and hearing membrane developed.

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