Rapid Fire
Sexual Dimorphism and Spider Silk Quality
- 24 Jan 2026
- 2 min read
A study has revealed that only large adult female Darwin’s bark spiders produce the toughest silk ever recorded in nature, showing how evolution optimises energy use, body size, and ecological need.
- Darwin’s bark spider (Caerostris darwini), native to Madagascar, produces silk with a tensile strength of about 1.6 gigapascals, making it around three times stronger than iron.
- However, this ability is restricted to large adult females, not males or juveniles.
- Sexual Dimorphism and Silk Quality: The study found a clear link between sexual dimorphism and silk quality, as females are 3–5 times larger than males and face greater ecological demands.
- Researchers analysed dragline (major ampullate) silk, the main structural silk of orb webs, and showed that its exceptional strength comes from high levels of proline, an amino acid crucial for elasticity and toughness, making silk production metabolically expensive.
- To manage this energy cost, adult females produce ultra-tough silk only when necessary, building sparser webs with fewer but stronger threads, while males and juveniles spin denser webs made of cheaper, weaker silk.
- This super-tough silk supports gigantic webs built over rivers and lakes, allowing females to capture prey inaccessible to other spiders. The study concludes that silk quality is adaptively regulated, and extreme strength evolves only when it provides a clear survival advantage.
- Notably, silk elasticity remains constant across all individuals, indicating it is a genetically conserved trait.
| Read more: New Genus of Jumping Spiders |
