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Humidity mediated performance and material properties of orb weaving spider adhesive droplets
Brent D Opell1, Hannah Mae Elmore1, Mary L Hendricks1
1Department of Biological Sciences, Virginia Tech Blacksburg, VA 24061 United States.
Acta Biomaterialia
|June 18, 2021
Summary
Spider web glue droplets adapt their stiffness to match the humidity of their environment. This adaptation ensures optimal insect capture for over 4,600 orb weaver species across diverse habitats.
Area of Science:
- Biomaterials Science
- Ecology
- Evolutionary Biology
Background:
- Orb spider webs utilize viscoelastic glue droplets to capture insect prey.
- These bioadhesive droplets rely on a hygroscopic aqueous layer, making their properties humidity-dependent.
- The adhesive performance and material properties of these droplets are crucial for spider survival.
Purpose of the Study:
- To test the hypothesis that natural selection has tuned orb spider glue droplet properties to species-specific foraging humidity.
- To characterize the humidity responsiveness and material properties of glue droplets from twelve orb spider species.
- To explore the biomimetic potential of these natural adhesives.
Main Methods:
- Tested adhesive properties (stiffness, toughness) of glue droplets from 12 species across a 70% relative humidity (RH) range (20-90%).
- Measured droplet extension lengths per protein core volume at different RH levels.
- Correlated droplet properties and humidity response with species' habitat and foraging behaviors.
Main Results:
- Significant inter-specific variation in stiffness (1088-fold) and toughness (147-fold) observed at 55% RH.
- Droplet extension peaked at lower humidities for species in dry habitats and higher humidities for those in humid or nocturnal habitats.
- Species-specific optimal stiffness achieved by tuning droplet hygroscopicity to foraging humidity.
Conclusions:
- Natural selection has optimized orb spider glue droplet properties for specific environmental humidities.
- An inverse relationship exists between droplet hygroscopicity and species' foraging humidity, ensuring optimal adhesive stiffness.
- These findings highlight the remarkable adaptation of spider silk glue and its potential for biomimetic applications.
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