The sex lives of venomous Sydney funnel-web spiders

The Sydney funnel-web spider, one of the world’s most venomous spiders, has a surprisingly safe sex life.

According to an international team of scientists, mating is a quieter – and less cannibalistic – affair than previously thought.

The researchers, who observed 451 videos totalling 165 minutes of footage of Sydney funnel-web spiders (Atrax robustus) mating, have published their findings in the Journal of Zoology.

“Some groups of spiders are still very poorly understood,” co-author Dr Bruno Buzatto, a terrestrial ecologist at Flinders University, tells Cosmos.

One of these groups, according to Buzatto, is mygalomorphs: a group that includes funnel-webs, trapdoor spiders and tarantulas.

“Because they went through this process called cryptic speciation, a lot of the times we have very similarly looking spiders that mostly differ in the mating genitalia, and structures that are involved in the mating courtship process.

“So very often, you have to look at those structures to assign a specimen to a certain species, even if it’s a described species.”

The Australian Reptile Park, on NSW’s Central Coast, has a breeding program for Sydney funnel-web spiders to milk their deadly venom to make antivenom: a substance which has ensured that no-one has died from a Sydney funnel-web spider bite since the early 1980s.

Read more: A Sydney funnel-web spider bite isn’t the end of the world

“Because of their breeding program, there are lots and lots of videos of them mating. And so we just used that to describe the mating processes,” says Buzatto.

This process included 13 distinct behaviours among the males, and four among the females.

Particularly surprising, according to Buzatto, was the way the females reacted when the male spiders lifted them into the air.

“They go into this quiescent state, where they don’t really move, and they’re very, very passive. It looks like they’re not reacting at all. This has been described the literature as catalepsy or quiescence.”

And the spur that male funnel-web spiders have on their second pair of legs – previously thought to defend them against being eaten by their sexual partner – actually serves another purpose.

“People usually think that in spiders, there’s a lot of sexual cannibalism: females eat males if you don’t do the courtship ritual well enough,” says Buzatto.

“That’s not really true – it’s actually quite rare in mygalomorphs.

“Sexual cannibalism is not as common as people might think.”

In fact, the spur on the males’ second pair of legs wouldn’t help distance them from females, because the male spiders pull females up to their first pair of legs. So why is it there?

“It’s more to provide some stability for the pair there, and perhaps helps the male secure the female for longer to transfer more sperm,” says Buzatto.

“It certainly doesn’t stop the female from attacking the male if she if she was trying to do that. Because they have big, big fangs, and when the female is propped up, her fangs are basically right on top of the male’s body. So if she was just basically bite down, she would get her fangs into the male straight away, and then the second leg doesn’t help.”

Buzatto says that there are likely differences between how the spiders behave in captivity compared to the wild.

“We try to study behaviour in the most natural settings possible. But unfortunately, sometimes the best we can do is in captivity.

“The thing with Sydney funnel-webs is they’re quite cryptic. The males are very seasonal, so they’re only out and about January to March usually, the summery season. And they’re not that abundant, it’s not like you see them everywhere.”

But these observations are barely scratching the surface of spider science.

“There are more undescribed species of spider in Australia than described species, by probably a factor of four or five,” says Buzatto.

“By looking at their morphology and their behaviours, we can start peeling species apart and have a better understanding of how many species we have, and which ones need conservation.”