(a,b) Caerostris darwini giant webs are suspended over rivers and lakes in Madagascar, such as the one in Ranomafana (a) and Andasibe (b); (c,d) large prey in C. darwini (c, with dragonfly) and Caerostris kuntneri (d, with beetle); (e) mating in C. kuntneri, highlighting sexual size dimorphism in Caerostris spiders (small male is on the right side on the female abdomen). Credit: Integrative Zoology (2025). DOI: 10.1111/1749-4877.70029

Dragline silk or major ampullate (MA) silk, the part of a spider’s web that forms the main frame and spokes, is one of the toughest materials known to science. That is, it can absorb massive amounts of energy from a sudden impact without breaking, outperforming most other natural materials and synthetic materials we’ve created, such as steel and Kevlar.

In a new study, scientists have examined silk toughness in two species of bark spiders (genus Caerostris) and found that females produce much stronger webs than males.

The research is published in the journal Integrative Zoology.

While it is known that silk toughness varies across species and that larger species tend to have tougher silk, little is known about variation within a single species across different life stages and sexes. Researchers chose to study bark spiders, which are native to Madagascar, because they produce the toughest silk, build the largest webs, and because adult females are often 10 to 100 times heavier than tiny adult males.

Stress-testing spider silk

The researchers collected egg sacs from wild spiders. They raised them in the lab, collecting silk from 40 individuals at different life stages and sexes (juvenile and adult females, juvenile and adult males). Then the silk fibers were stress-tested—stretched until they snapped—to see how much energy they could absorb.

The team found that only adult females produce truly exceptional silk that is significantly tougher and more resistant to initial stretching (stiffness). All males and juvenile females produce inferior silk that is much easier to stretch, meaning it isn’t tough enough to absorb the high energy of large prey.

"Our study shows that the exceptional toughness of Caerostris MA silk is limited to adult females and is not found in juveniles or males," wrote the research team in the paper. "The increased toughness in adult female Caerostris MA silk is consistent with the hypothesis that larger orb-weaving spiders, especially species with sparser webs, are under selection to produce webs that can capture larger prey."

The cost of quality

The findings are an illustration of ontogenetic plasticity, the way organisms respond to environmental change throughout development. So bark spiders change the properties of their silk based on their size and life stage. The researchers suggest that the differences exist because producing highly tough silk is metabolically costly. Therefore, juveniles and males avoid this cost by producing inferior silk that is still strong enough to catch and trap some prey.

But when females reach adult size, they switch on super-tough silk production to support their massive webs and the large prey they must catch.

Written for you by our author Paul Arnold, edited by Stephanie Baum, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You’ll get an ad-free account as a thank-you.

More information: Matjaž Gregorič et al, Extreme Silk Toughness in Caerostris Spiders Is Limited to Adult Females, Integrative Zoology (2025). DOI: 10.1111/1749-4877.70029

© 2025 Science X Network

Citation: Adult female bark spiders produce superior and tougher silk than males do (2025, December 9) retrieved 9 December 2025 from https://phys.org/news/2025-12-adult-female-bark-spiders-superior.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.