One of the deadliest spiders in the world has developed its extremely toxic venom to protect itself during the annual “mating season”
The venom of Australian funnel-web spiders contains δ-hexatoxins (δ-HXTXs) – venom peptides that make the venom dangerous to humans and primates.
It is estimated that between 30 and 40 people are bitten each year. During all the observations, 13 deaths were reported.
The poison affects the nervous system, blocking nerve impulses to the muscles, which causes paralysis of the entire nervous system. Symptoms include muscle twitching, shortness of breath, rapid heart rate, and high blood pressure.
Scientists know that male Australian funnel spiders are much more toxic than females. They also know that their venom does not act on other mammals in the same way it does on humans and primates, but why this happens still remains unknown.
In a study published in PNAS, researchers led by Brian Fry from the University of Queensland studied the venom of 10 different spider species to better understand why male bites are so dangerous to humans and vertebrate predators.
Through their genetic analysis, the team was able to show the evolutionary path that led to the emergence of the primate-targeted venom. The results showed a “remarkable conservation sequence” for delta-hexatoxins, suggesting that the poison was developed to perform a protective function.
During the mating season in the summer months, male funnel spiders leave their nests in search of a partner.
“It’s a dangerous ritual for males. They travel long distances in search of females. This can be quite risky, because it threatens to meet with vertebrates insects such as Dunnart. It’s small, narrow-footed marsupials that look like a mouse,” Fry said.
The results showed that the venom of the funnel-web spider was originally intended to target insects, including flies and cockroaches. However, it seems that natural selection has caused it to become a protective poison against vertebrate predators.
“Toxicity to humans is just an ‘evolutionary coincidence,'” the researchers say.