Photo worth seeing: Woodlouse spider with a unique selling point

Photo worth seeing: Woodlouse spider with a unique selling point
The Antarctic giant isopod spider (Colossendeis megalonyx) © R. Robbins

More than 1,300 species of water-dwelling woodlice spiders (Pycnogonida) are known worldwide. While most representatives of these spider-like invertebrates are smaller than a fingernail, very large isopod spiders can occasionally be found in colder seas such as the Antarctic Ocean. These can reach leg spans, i.e. the distance from the tip of one leg to the tip of the opposite leg, of more than 30 centimeters. However, so far little is known about the lifestyle and reproduction of these comparatively huge species of woodlice spiders.

“In most isopod spiders, the male parent takes care of the babies by carrying them around as they develop,” explains lead author Amy Moran from the University of Hawai’i at Manoa. “Strangely, despite descriptions and research going back over 140 years, no one has ever seen the giant Antarctic spiders brood their young.” That’s why Moran and her colleagues Aaron Toh and Graham Lobert headed to Antarctica in October 2021 to answer this question.

During their expedition, the research team gained insightful new insights into the reproductive habits and behavior of the Antarctic giant isopod spiders. To do this, they dived into the depths of the icy Arctic Ocean and collected groups of mating isopod spiders for detailed analysis in the laboratory.

To the researchers’ surprise, the woodlice spiders produced thousands of tiny eggs a few days after mating. However, these were not carried around by the parents until birth, as expected. Instead, one parent – likely the father – spent two days attaching the eggs to the rocky bottom of the pool, the team reports. There the offspring continued to develop until after a few months the small larvae hatched.

“In these giant isopod spiders, the males care for the offspring, but they do this differently and in a simpler way than with most other isopod spiders,” says Moran. Nevertheless, this reproductive strategy also appears to be successful. As the researchers observed, the eggs attached to the rocky subsoil are quickly overgrown by algae, which gives them excellent camouflage. Even for the experienced biologists, it was difficult to discover the eggs that had already been located, the team reports.

“We were so lucky to be able to see this. “The opportunity to work directly with these amazing animals in Antarctica meant we were able to learn things that no one had ever imagined,” says Toh.

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