When funnel-web spiders evolved millions of years ago, toxins in its venom mainly targeted their natural prey: insects such as cockroaches and flies. We examined the genetic sequences of all delta-hexatoxins in funnel web venom. We found over time, the venom of adult males evolved to be potent to vertebrate predators. Unluckily for humans, who are vertebrate animals, we copped it in the process.
Female funnel webs stay safely in their burrows and let the males come to them. So the venom of females is thought to remain potent only against insects their entire lives. Now armed with a stronger understanding of how delta-hexatoxins evolved, we want to put that knowledge to use.
The new genetic sequences we discovered will enable a better understanding of what funnel web spider venom does to the human body. This could be critical for improving existing anti-venoms, and for designing evidence-based treatment strategies for bite victims. But perhaps its some comfort to know their venom is not targeted against us, and the potential lethal effects are just a stroke of evolutionary bad luck.
This article is republished from The Conversation under a Creative Commons license. Read the original article. Close Menu. Facebook Twitter Instagram Instagram Adventure. How climate scientists talk to their kids about the climate crisis We chat to three climate scientists from the University of New South Wales about how they talk to their kids about the climate crisis. Newsletter Get great photography, travel tips and exclusive deals delivered to your inbox.
Email Address Required. First Name. Last Name. The tunnel leads back into a short surface chamber from which the burrow descends.
The burrow is often weakly silk-lined and rarely more than 30 cm deep. The spider hunting mostly at night sits just inside the entrance with its front legs on the trip-lines. When a beetle, cockroach, or small skink, typical items of funnel web food, walks across the lines, the spider senses the vibrations and races out to grab its meal. The prey is quickly subdued by an injection of venom from the spider's large fangs. Funnel-web spiders may also forage on the surface in the vicinity of the burrow.
Holes are normally found in moist, shaded areas like rockeries, dense shrubs, logs and leaf litter. A small, neat hole lined with a collar of silk which does not extend more than a centimetre from the rim could belong to a trapdoor spider the common Brown Trapdoor Spider does not build a 'door' for its burrow.
Other possible hole owners include mouse spiders, wolf spiders or insects most commonly cicadas or ants. Most funnel-webs are ground dwellers but a few live in trees. The largest of all funnel-webs is the Northern Tree Funnel-web Spider, Hadronyche formidabilis , reaching 4 cm - 5 cm body length.
These spiders live in the wet forests of northern New South Wales and southern Queensland and have been found over 30 m above ground. While many have their retreats in surface-opening branch rot-holes, some spiders appear to live and feed entirely inside the deadwood pipe of large forest trees like Tallow-wood, feeding on beetles and other insects inside this rotting wood habitat.
The abdomen sometimes has a light plum colouration. They make silk-lined retreats in holes and rot-crevices in a variety of rough-barked trees, including Melaleuca paperbarks , Banksia , Casuarina she-oaks and eucalypts. The exposed web surface tunnel is disguised by a covering of bark or wood particles. There are often two entrances, each with trip-lines running out across the bark. Prey ranging from beetles to tree frogs are taken by these spiders. Chemicals called pheromones in the female's tripline silk help the male locate and identify her burrow.
Well before mating, the male spins a small silk sperm web, onto which he deposits a droplet of sperm from his abdominal genital pore. The sperm it is then taken up and stored in the mating organs at the ends of the male's palps. During mating, considerable sparring occurs until the female accepts the male.
Both spiders rear up with first legs raised against each other, while the male engages his mating spurs across the bases of the female's second legs. The male then inseminates the female by inserting the tips of his palpal organs into the female's genital opening on the underside of her abdomen. Only male spiders have been responsible for all recorded funnel-web envenomation deaths - why is it so?
The answer lies in a combination of spider behaviour, venom chemistry, and even colonial politics. During the warmer months of the year November-April male funnel-webs wander about at night looking for females in their burrows. Males wandering in suburban gardens may sometimes become trapped inside houses or garages, especially those with concrete slab foundations where entry points under doors are easily reached.
The venom of the male Sydney Funnel-web Spider is very toxic. This is because male spider venom contains a unique component called Robustoxin d-Atracotoxin-Ar1 that severely and similarly affects the nervous systems of humans and monkeys, but not of other mammals.
The absence of this chemical from female Sydney Funnel-web Spider venom explains why bites by these females have not caused any deaths. However, not all funnel-web species show such a large gender-based difference in venom toxicity. Almost four million people live in the Sydney region, the centre of the distribution of the Sydney Funnel-web Spider.
This makes the likelihood of human encounters with this spider much greater than in less urbanised areas like the Blue Mountains. This situation, of course, stems from a political decision made in London more than years ago, to establish a colony in 'New South Wales' at Sydney Cove, a site nominated by Captain James Cook after his voyage of exploration. Taken together, these ingredients produce a recipe for unexpected and potentially life-threatening encounters.
No deaths have occurred since its introduction. Much of the venom for this research was supplied through a funnel-web venom milking program at the Australian Reptile Park. Most ground dwellers will occupy naturally occurring spaces beneath rocks and logs, and line the interior with silk.
Many species have multiple entrances which are tube-like openings of silk, usually with some distinct silk strands trip lines connected to them. These lines alert the spider of the presence of prey when they are hunting. Insects, spiders and small vertebrates such as lizards and frogs are taken by funnel-web spiders. The prey is simply ambushed and overpowered, bitten and dragged back inside the retreat to be consumed.
A funnel-web in a hunting position at the entrance to its retreat. A Sydney Funnel-web Atrax robustus ready to ambush prey at an entrance to its burrow. These spiders will often have multiple sock-like entrances like this one. The approximate distribution of funnel-web spiders within Australia. The Sydney Funnel-web left and the various funnel-web species together right.
They have their share of predators, even some which will take them on within their lairs. Centipedes are expert funnel-web predators, and will readily enter the retreat, attack and consume the occupant.
0コメント