Increasing spider populations and climate change: should we be worried?

Australia has a reputation for dangerous spiders, with currently more than 2000 identified species. Now there is more reason than ever for Australians to fear climate change, new research shows.

By REBEKAH HILLAN

Australia’s spider population may be dramatically rising as a result of global warming – causing many species to become more common and possibly even able to run faster.

The Australian Bureau of Meteorology’s monthly report showed this March was the hottest on record, reaching 1.7C above the long-term average, with April not far behind as the second hottest on record.

The Australian Museum's manager of the Search and Discovery Section, David Bock, said the rise and fall of spider numbers in Australia had become more dramatic, leading to significant population increases during the summer months.

“We are noticing a lot more erratic temperatures. These sorts of conditions really influence the insect populations to increase dramatically, which then leads to the spider population increasing,” he said.

“We have noticed a lot more overall public enquiries coming in for a whole range of spiders,” Mr Bock said. Spiders may also become quicker on their feet, according to recent experiments documenting the speed and coordination of tarantulas in different temperatures.

An article published in the Journal of Experimental Biology showed the rising temperature levels caused the fluid in spiders’ legs to circulate faster. This allowed them to run at higher speeds during hot weather. They also became clumsier and less coordinated, increasing the likelihood that they will accidentally drop from trees or ceilings on to the unsuspecting heads of those below.

Some of the most common spiders that you may notice more during the heat in Victoria include orb-weavers, redbacks, huntsmen and white-tailed spiders.

Orb weavers

Spiders of the orb weaving variety are especially prevalent in trees.

“If you’re standing out at night and see those big webs in trees, these tend to be made by spiders from the orb weaving group,” Mr Bock said.

“They’re the ones you tend to walk into at night.”

Orb weavers are aggressive, and are the most common spider species to bite. Their venom only causes local, minor pain and is not generally dangerous to humans. They can measure anywhere between 1.5cm and 3cm.

Redbacks

Redbacks commonly hide in dry, sheltered areas, often found in garden sheds and mailboxes. Bites from redbacks occur most frequently in the summer months.

Their venom affects the nervous system causing severe, persistent pain, nausea and lethargy. although redback spider bites can lead to death if left untreated, there have been no recorded fatalities since 1979.

Huntsman

Huntsmen spiders are reluctant to bite and are more likely to run away if approached. Their venom is not considered dangerous to humans and causes only minor localised pain.

They are most dangerous in cars. When drivers react to a huntsman crawling out from behind the dashboard or sun visor it can cause an accident. A female huntsman can reach up to an intimidating size of 17cm.

White-tailed spiders

White-tailed spiders have a dark reddish-grey body with orange and brown banded legs. Their venom is not usually dangerous to humans and can cause minor localised pain.

There have been claims that their venom is linked to severe skin ulceration in humans, but these are disputed by the scientific community. White-tailed spiders can reach up to 18mm, and are more active at night.

For those of us who are afraid of spiders, David Bock believes facing your fears and learning more about their biology will help.

“Last time we put on an exhibition, there were lots of people coming with the fear of spiders because they were facing their fears,” Mr Bock said.

The Australian Museum is putting on another exhibition in October. This is a perfect opportunity for arachnophobes to address their phobia before the summer months. In the meantime, spider populations will temporarily decrease during winter, so get outside and enjoy the outdoors while there is still hope.