Ancient assassin spider, feared extinct after fires, has been discovered on Kangaroo Island

2021-11-17

An ancient species of spider, feared extinct after devastating bushfires tore through Kangaroo Island in the summer of 2020, has been found alive.

Key points:

• An adult female and a juvenile were found

• They were found in a small patch outside their known range

• The species recovery is still tenuous and will be up against genetic bottlenecks and habitat loss

The assassin spider, also called the pelican spider (Zephyrarchaea austini), was only known to live in the Western River Regional Protection Area on Kangaroo Island.

That area was razed in the massive bushfire that burnt through more than 200,000 hectares of bush and farmland across the island nearly 2 years ago.

But two individuals — a female and a juvenile — have been found in a small patch of leaf litter, according to Jessica Marsh, an honorary research associate at the South Australian Museum.

While the researchers are keeping the exact location under wraps, it was outside the previous known range of the spider on Kangaroo Island, Dr Marsh said.

“It was amazing! We’d been searching since the fires. [We] had just about given up hope.

“These spiders don’t disperse far, so it’s very unlikely they’ve moved there before the fires.”

The discovery was made at the end of September, but the announcement was delayed until DNA testing could confirm it was the same species of assassin spider.

The spider dates back to the Jurassic period, and is called an assassin for the way it hunts other spiders.

It’s considered to play a crucial role as a regulator of spiders within the food web.

Given that the spider has been found outside its known range, Dr Marsh said her team would keep expanding their search, which has been funded by the Landcare Led Bushfire Recovery Grants Program.

“I’m not confident that we’ve got all of them,” she said.

“I think there may be other pockets out there and we’ll keep searching.”

She said the focus at this stage would be on locating and protecting any more populations if they find them, but that they may consider intervening to assist in recovery, such as through captive breeding, down the track.

Recovery, if it happens, will be slow

The discovery of a juvenile is a promising sign that breeding has happened since the bushfires.

But recovery of the species is still extremely tenuous.

It’s likely the population has gone through what is known as a genetic bottleneck.

There will likely be far less genetic diversity between the remaining spiders than in the previous population, meaning if a new population is able to establish, it could be less resilient to stressors.

And there are other challenges to its recovery, Dr Marsh said.

“There are several things that aren’t on their side.

“Low dispersal is a key one. And the habitat they live in, it’s going to take a long time for that habitat to regrow.”

The spiders are habitat specialists, living in dense vegetation along creek lines.

Where they have been discovered is in some very small remaining pockets of that habitat, Dr Marsh said.

“It shows us how important those little pockets are,” she said.

“It give us hope but, it’s also a warning sign.”

Only about a third of invertebrate species in Australia have been described by science, according to Dr Marsh.

Many may be threatened or have already gone extinct without us identifying them or understanding their ecosystem functions.

“There is a massive amount [of species] that are under threat,” she said.

“We’re not talking about extinction in isolation. When it’s more species and more land lost, we may start to notice.”

abc.net.au, 17 November 2021
; https://www.abc.net.au