Huge Nest of Huntsman Spiders Discovered in Box Built for Pygmy Possums

An Australian conservation group which set up nests for fluffy pygmy possums on a nature reserve was shocked to discover dozens of huge spiders had moved in instead.

The photo shared by Bush Heritage Australia shows a nest box on the Monjebup North nature reserve in south-west Western Australia, around 140 kilometers north-east of Albany, packed with huntsman spiders.

"Ever lifted up a lid to find an unexpected SPIDER lurking beneath? How about dozens?" the non-profit organization wrote alongside the image. Bush Heritage Australia ecologist Angela Sanders discovered the creepy crawlies, according to the post.

Unlike most spiders who are solitary, members of the delena cancerides species live in groups. This behavior earns them the name the social huntsman.

In January 2017, the organization set up 20 nest boxes for pygmy possums in the vegetation restoration area covering 450 hectares of former farmland, as part of the Gondwana Link conservation project.

Sanders explained in a blog post last month: "Pygmy Possums quickly took up residence in the nest boxes we erected in restored habitat at our Monjebup North reserve in southwest WA. What we didn't expect were the large colonies of social spiders that also moved in!"

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"It all started about the same time we were finding Pygmy Possums in the boxes, but on lifting the lids of some we found many huntsman spiders of all sizes whizzing around inside," said Sanders.

These spiders usually live under the dead bark of trees, and don't have webs. As there isn't much tree bark in the restoration area at the moment, the spiders moved into the wooden boxes instead, Sanders said.

In a Facebook comment, Bush Heritage Australia explained: "As these revegetation areas mature the habitat becomes richer and more complex and is able to support a higher diversity of species.

"There is now enough food for the huntsman spiders and pygmy possums, but the trees are not yet old enough to have the hollows, fallen timber and thick loose bark they need for shelter. So we've erected lots of nestboxes that both these species and others are competing for."

Colonies of social huntsman spiders feature a single adult female, who lays eggs. Instead of using webs to catch their prey like other spiders, these arachnids will stand and wait to grab their dinner, or chase after it.

"A single adult female lays eggs and the successive generations of siblings help each other out and share prey items," Sanders wrote. "This has several advantages for the spiders including faster growth. They're also heavier and healthier."

The photo got a lot of interest on Facebook, garnering around 1,300 likes, and 1,200 comments.

"Well. Isn't that just a big pile of NOPE!!!" joked one user.

Some users wanted to know what happened to the possums that the boxes were intended for.

Bush Heritage Australia explained: "there are plenty of boxes without spider colonies and with possums."

The possums sometimes live in nest boxes with a "few spiders." Although some huntsmen in Queensland hunt mice, these spiders aren't as big as those. In fact, the possums will probably eat the smaller huntsmen, according to the group.

Sanders told Newsweek: "We certainly [did] jump back a bit when we opened a box seething with spiders, as they do run up your arm if you're not quick enough!

"However, it's also a great feeling because huntsman spiders being in the nest boxes suggests improved ecosystem complexity. The spiders feed on insects and other invertebrates and lay their egg sac inside the box," she said.

She added: "Huntsman Spiders aren't harmful to humans and they're very useful in controlling insects like mosquitos and cockroaches."

This article has been updated with comment from Angela Sanders.

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A stock image shows a huntsman spider. A conservation group discovered the delena cacerides species in boxes intended for possums. Getty