Male grasshoppers (Glyptobothrus maritimus) in roadside habitats have increased stridulatory sound-producing organs.

Anthropogenic noise disrupts animal communication, often prompting shifts toward higher-frequency signals to avoid masking by low-frequency noise. While such changes are typically attributed to behavioral plasticity in vocal species, this may not apply to non-vocal sound producers. We tested whether male grasshoppers (Glyptobothrus maritimus) exhibit morphological changes in response to noise by examining stridulatory organ density and courtship signal frequencies across habitats with varying traffic noise. In the first survey year, grasshoppers from the noisiest habitats had 13.4% higher organ density-a trait that may favor higher-frequency signals-than those from the quietest habitats. However, this difference became unclear in the following year. Additionally, courtship signal frequencies showed no positive relationship with organ density or noise. These findings suggest that elevated sound levels can induce short-term developmental processes that generate variation in sound-producing organs in non-vocal animals, underscoring how neglecting morphological plasticity, independent of signal modification, constrains understanding of ecological noise impacts.