One of the most captivating spiders in existence is Darwin’s bark spider, found in the lush forests of eastern Madagascar. Although not discovered by Charles Darwin himself (it was actually found in 2009), it was named in commemoration of the 150th anniversary of the publication of “On the Origin of Species.”

The species is renowned for its remarkable web-building abilities. These spiders construct the largest orb webs in the world, with some spanning up to 2.8 square meters and stretching across entire rivers, reaching widths of up to 25 meters. These massive webs enable them to ensnare numerous river insects, particularly mayflies, in one go.

What makes these webs even more extraordinary is the material they are made of. Darwin’s bark spider silk is the toughest biological substance known to humans, surpassing all others by a factor of two. Its tensile toughness can reach up to 520 Joules per cubic meter, making it ten times stronger than Kevlar when comparing equivalent areas.

However, today we delve into the intriguing mating habits of Darwin’s bark spider, which feature an assortment of behaviors that are typically associated with other spider species but are uniquely combined in this particular species:

The male approaches a female who is at least three times his size. Given the potential risk of being eaten, males usually prefer females that have recently molted, as their exoskeleton is still soft and less agile, increasing the male’s chances of survival.

The male ensnares the female in his silk. This serves as an additional precautionary measure to reduce the likelihood of being devoured. However, the silk, in small quantities, tends to hinder the female more than it acts as a fail-safe restraint. The male’s survival is not yet guaranteed.

As an additional preventive measure, the male occasionally secretes saliva onto the female’s reproductive organs, known as the epigyne, using his palp organs located near the mouth. This saliva seems to have a calming effect on the female, reducing her aggression.

Copulation takes place, with sperm transferred via the palps. However, in approximately half of observed cases, the male’s palps break off and remain inside the female. This serves a purpose: the severed reproductive organs act as a plug, preventing other males from passing on their genes.

After mating, the male does something rather surprising. If his palps have not already detached inside the female, he self-castrates by chewing them off. This self-castration triggers a hormonal change, making the male more aggressive. He becomes better equipped to fend off rival males and protect his genetic lineage.

As you can see, the mating habits of Darwin’s bark spider are quite peculiar. While my previous answer touched on the species’ web-building and silk, leaving the mating behaviors for another discussion, today we have delved into the fascinating aspects of their sex life.