It is a bit disconcerting for a Kiwi, who grew up in New Zealand with no poisonous spiders apart from the very rare Katipo, to be now living in the bush side by side with one of the most venomous spiders in the world. We recently found a male Funnel-web spider in our pool. We placed him in a jar even though he looked quite dead and sure enough within a few hours he was raising his front legs and baring his fangs in an aggressive threat pose.
I felt compelled to find out a bit more about the infamous Funnel-web focusing mainly on the Sydney Funnel-web Atrax robustus which occurs approximately within a 120 km radius of Sydney. Most articles about the Funnel-web spider focus on how venomous they are but for me the most interesting aspect was the significantly different lifecycle of the female and male. The female spends most of her life which can be up to 12 years inside or close to her burrow whereas the male only lives for 3 to 4 years. Funnel-webs have eight simple eyes clustered closely together but their vision is poor, most likely limited to the detection of movement and variations in light.
The Funnel-web is an ancient spider which evolved when Australia was covered almost entirely by humid forests some 50 million years ago. They are susceptible to drying out so need moist environments and the male is likely to be more active in humid or wet weather. They make their burrow in predominantly moist and soft ground where it is easy to dig. They prefer sheltered habitats such as beneath logs, leaf litter, dense shrubs, rocks or where there is a natural crevice. The female is slightly larger than the male at around 3.5cm body length (males are more lightly built with longer legs). They build a silk lined burrow which is rarely more than 30cm in length. It has a series of irregular silk trip-lines emerging from the 2.5 cm more or less crescent shaped entrance. It will be in a spot where the sun does not pass directly over the hole.
Deep at the end of the burrow is a purse-like enclosure where the spider rests during the day. At night near the entrance of the tunnel it waits, front legs resting on the trip-lines for vibrations radiating from prey walking across the lines. It will quickly emerge to claim its prey which could be a beetle, cockroach, insect larvae, millipede, skink or frog, and then hurriedly retreat back to its burrow.
Once the male has reached sexual maturity which takes 2-3 years, he will leave his nest in search of a female. Pheromones in the female’s trip-line silk help the male locate her burrow. It is the wandering male in Summer and Autumn that is responsible for most bites.
Having found a female’s burrow the male spins a small silk sperm web, deposits a droplet of sperm and stores it in the mating organs at the ends of his pedipalps which are the small appendages near his mouthparts. He performs an elaborate courtship routine to identify himself as a mate and not a potential prey. Spurs on his second leg are used to hold the female during mating. He inseminates the female by inserting the tips of his pedipalps into her genital opening on the underside of her abdomen. It is thought that the male stops eating once he leaves his nest in search of a female and will generally survive only 6-12 months after mating.
After mating the female will wrap the 100 or so eggs in a silk case and attach it near the end of the burrow. The female will take great care to clean and turn the egg sac and the spiderlings will emerge after around 3 weeks. They will stay with their mother moulting their exoskeleton once or twice, before leaving to excavate their own homes.
Funnel-web venom is harmless to most animals including cats, dogs, rabbits and guinea pigs. They are easy prey for chickens, bluetongues, flatworms and velvet worms immobilise them with a sticky spray before eating them. Large lizards take roaming males and centipedes and white-tailed spiders will happily feast on a funnel-web. They are also susceptible to fungal infections due to their preference for humid environments.
The funnel-web may be discovered by inadvertently digging around in the garden. The bite of the male is five times more deadly than the female. They are fairly aggressive and will bite at the slightest provocation. However it cannot jump or climb a smooth glass surface so you are quite safe if it is in a jar. The fangs are very powerful and it can bite through gloves, shoe leather and fingernails.
If the male is searching for a female he is vulnerable to drying out so he is always on the lookout for a shelter. He may end up in the pool filter, or even inside boots left outside. Fitting draft excluders and fly-screens to windows will prevent climbing spiders from obtaining access.
Funnel-webs normally only bite humans when agitated or provoked, often biting repeatedly, however they only release a single dose of venom. A “dry bite” where venom is not released or has been released into clothing explains why antivenom isn’t needed in at least 90 per cent of cases. Once the deadly toxin has been released the spider can take up to a month to build up enough venom to again be a threat.
Treatment is similar to a snake bite which is to wrap a bandage firmly around the affected area and to try and keep calm and the area affected immobile. Collect the spider if at all possible to ensure that the spider is correctly identified, and get to a hospital pronto. A small child has been known to die within 15 minutes from a bite with a substantial envenomation. A team of medical researchers led by Melbourne-based Struan Sutherland developed the first successful antivenom and since 1981 no one has died in Australia from the bite of a Funnel-web.
Spiders play a very important part of our ecosystem keeping many insects under control and also as food for its predators. Our best weapon against the funnel-web is knowledge so that we can be aware of their behaviour, the type of habitat they prefer and keep our wits about us when we are in their habitat. Fortunately we also have access to the antivenom if a bite occurs.
Also a big thank you to Dr Mike Grey of the Australian Museum for minor alterations and checking the article for accuracy.