Study Reveals Why Bark Spiders Produce Exceptionally Tough Silk

Scientists have studied bark spiders to understand the conditions under which they produce their famously tough silk. The findings were recently published in the journal Integrative Zoology.

Species Studied

The research focused on two bark spider species found in Madagascar:

• Darwin’s bark spider (Caerostris darwini), known for spinning the largest orb webs ever recorded, and
• Its close relative, (Caerostris kuntneri).

Toughest Biological Material Known

One of the strongest materials on Earth is not factory-made but spun by a spider barely two inches long.

• The silk of Darwin’s bark spider has a tensile strength of about 1.6 gigapascals,
• Nearly three times stronger than iron, and
• Stronger and tougher than most human-made fibres, making it the toughest biological material ever tested.

However, scientists have found that not every individual spider produces silk of this exceptional quality.

Body Size and Silk Quality

Across spider species, body size is closely linked to silk quality.

• Larger spiders generally produce tougher silk to capture larger or faster prey.
• In orb-weaving spiders like C. darwini, evolutionary increases in body size have been accompanied by larger webs and stronger silk threads.

Role of Dragline Silk

Dragline silk is one of the most important types of spider silk:

• It forms the structural backbone of an orb web,
• Acts as anchor threads, safety lines, and emergency escape ropes, and
• Is nearly invisible to the naked eye.

High Energy Cost of Strong Silk

Producing dragline silk is metabolically expensive.

• The synthesis of silk requires specific amino acids,
• Some, like proline, are especially energy-intensive to produce.
• Darwin’s bark spider silk contains unusually high levels of proline, which gives it exceptional strength and elasticity.

Source; TH