Humidity induces structural colour change and contributes to biogeographic colour variation in sweat bees
Madeleine M Ostwald1,2, Leslie Cervantes Rivera2, Jorge De La Cruz2
1School of Biological and Behavioural Sciences, Queen Mary University of London, London, UK.
Biology Letters
|April 22, 2026
Summary
Climate change impacts bee coloration. Humidity causes reversible color shifts in sweat bees (Agapostemon subtilior), changing from blue-green to coppery green. This demonstrates how environmental factors influence insect structural coloration.
Area of Science:
- Zoology
- Ecology
- Biophysics
Background:
- Dynamic coloration is crucial for animal communication, but climate's passive effects on baseline coloration are understudied.
- Reversible color changes are known in animal communication, yet humidity's influence on insect cuticle color is poorly understood.
Purpose of the Study:
- To experimentally demonstrate reversible, humidity-induced color change in bees.
- To investigate if climate, specifically humidity, influences wild bee coloration patterns.
Main Methods:
- Controlled laboratory experiments exposing sweat bees (Agapostemon subtilior) to varying relative humidity levels.
- Analysis of crowd-sourced field images to correlate bee coloration with ambient humidity across their range.
Main Results:
- Relative humidity significantly alters A. subtilior cuticle color within 24 hours, shifting from blue-green (low humidity) to coppery green (high humidity).
- Older bee specimens showed more pronounced color shifts, suggesting cuticular degradation amplifies humidity effects.
- Field data indicated ambient humidity weakly predicts coloration variation in A. subtilior, consistent with lab findings.
Conclusions:
- Climate, particularly humidity, modulates structural coloration in bees.
- Abiotic conditions play a significant role in shaping dynamic visual traits in insects.
- The observed color shifts may result from moisture-induced swelling of cuticular multilayer structures.
