Friday, May 19, 2006

Friday Spider Blogging

Science (Spider) Friday: Sydney Funnel-Web

(Previous Spider Fridays: The Black Widow)

Hello, and welcome to this week's edition of Spider Friday--your opportunity to learn more about the fascinating spiders that inhabit our pale blue dot. This week, we'll venture down under to examine what is perhaps the most dangerous spider in the world--the Sydney Funnel-Web.

So put another shrimp on the barbie and come along for the ride.


Kingom: Animalia
Phylum: Arthoropoda
Class: Arachnida
Order: Araneae
Infraorder: Mygalomorphae
Family: Hexathelidae
Genus: Atrax or Hadronyche


BACKGROUND:

You know, there are a bunch of people out there that say "spider" like it's a dirty word. And usually, I'm the one telling them that spiders are our friends. They help us out, and all they really want is to be left alone to eat their fill of insects in peace. But if there's one spider that provides the counterexample to this, it's the Sydney Funnel-Web. It just doesn't like you. But don't take it personally. It doesn't like anyone else either. And it has the power to back it up. The Sydney Funnel-Web is one of the most aggressive spiders known, and unlike most spiders who just want to run away if they can, the Sydney Funnel-Web will not hesitate to bite if given the opportunity.





The Hexathelidae (funnel-web) family of spiders lies within the infraorder of Mygalomorph spiders--an infraorder which includes the bigger, stockier hunting spiders like tarantulas, trapdoor spiders and wolf spiders. There are several genera within the Hexathelidae family, but of these, only two are dangerous: the Hadronyche genus, which includes several funnel-webs with dangerous venom, such as the extremely dangerous, but rarely encountered, H. formidabilis, the Northern Funnel-Web, and the dangerous Queensland and Toowoomba funnel-web spiders; and the Atrax genus, which has only one species: A. robustus, the Sydney Funnel-Web.

Thankfully for us in America, the dangerous spiders of the Hexathelidae family are only found along the Southeast coast of Australia--though a few stragglers have been observed in Tasmania and the Solomon Islands:



And the Sydney Funnel-Web has an even smaller distrubution--it is only found within a roughly 75-mile radius around the city of Sydney. But unfortunately for the residents of Sydney, the life cycle of the Sydney Funnel-Web make it extremely susceptible to human contact.

The body of a fully-grown Sydney Funnel-Web is about 1 1/2 inches long. The carapace and legs are a shiny black, with little noticeable hair. The abdomen is of a lighter color, generally dark brown or dark purple. It's a stalky spider, but like most Mygalomorphs, it is capable of moving plenty fast when it sets its mind to it.

Funnel-Webs will eat anything of adequate size that happens to come near their burrow. Usually this will include insects, such as cockroaches:



But it can include anything else, as well, including lizards:



LIFECYCLE:

Like many mygalomorph spiders, including tarantulas, Funnel-Webs need humidity to keep going--when exposed to direct heat and sunlight, they dessicate and die rather quickly. They will either use convenient crevices to form a burrow, or will dig one themselves. The burrows are easily recognizable owing to the general funnel shape, and the silk tripwires which radiate out from the burrow like spokes from a wheel.





Sydney Funnel-Webs generally mature a couple of years after hatching. While females can live up to eight years, males only live a couple of months after their final molt, at which point they leave their burrows to focus exclusively on finding a mate and give up eating, usually dying within a few months. Because females tend to remain in their burrows unless disturbed, most unfortunate encounters with Funnel-Webs are usually the result of running into a male wanderer in the evening, or accidentally disturbing a male's resting spot during the heat of the day. Females produce an yellow-green pillow-shaped egg sac containing about 50-150 eggs. The spiderlings go through two molts in the protection of mom's burrow before venturing out to make their own.

(Spiderlings of H. infensa, the very dangerous Toowoomba Funnel-Web)

Males and females have morphological differences that can be recognized by a trained observer. Males are more slender, but also have hooks at the end of their pedipalps (the short leg-like appendages on each side of the fangs) with specialized grooves that facilitate the transfer of sperm to the female's sex organs. In addition, males have a hook on each leg of the second leg pair--this hook serves to prevent the female's fangs from snapping down on the male during mating.


(A. robustus; male at left, female at right)

(H. formidabilis mating; male at left, female at right).

BITES:

If you live in Sydney, you already know what to do. If you're traveling there and some big, black spider has just delved its fangs into you, apply a tourniquet IMMEDIATELY and call for medical assistance.

13 people have been known to have died from Sydney Funnel-Web bites, with deaths ranging in time from 15 minutes for children to several hours for an adult. All known fatalities have been confirmed to have come from male spiders. Severe allergic reactions resulting in anaphylactic shock is also possible, which was usually the undoing of victims that weren't either children, old or otherwise infirm. Fortunately, there have not been any deaths from Funnel-Webs since the introduction of a very capable anti-venin in 1981. This antivenin is effective for all dangerous members of the Hexathelidae family. Antivenin is reserved for the most dangerous 10% of cases, usually involving children or the elderly, as antivenin, like all homeopathic vaccinations, carries a risk of side effects.

The venom of the Sydney Funnel-Web is a strong neurotoxin, called Atraxtoxin. This poison is very light in terms of molecular weight, which contributes to rapid manifestation of symptoms, such as profuse sweating and salivation, tachycardia, hyperventilation and severe abdominal cramping. The effects of the venom usually wears off in a few hours, with no lasting effects.

Surprisingly, the sexual dimorphism in bites between male and female spiders goes along opposite lines from the black widow discussed last week. The male Funnel-Web's venom is thought to be five times more toxic than the bite of the female, though the female's is dangerous as well--an unfortunate happenstance, given the fact that most bites are delivered by wandering males.

Before a Funnel-Web bites, it goes into a characteristic, and very menacing stance, in which is raises its entire body up off the ground:



The spider will then snap down its carapace (the "head" section) like a trapdoor, resulting in a bite of incredible force. Funnel-Webs have been known to to bite straight through fingernails, leaving the fangs embedded in the cuticle beneath. There has also been a case of a Funnel-Web biting through a soft shoe and hitting the skin below.

Sometimes, though, this can be a boon to the victim: Although many spiders will do venomless "dry bites" in self defense, Funnel-Webs generally don't. Before biting, Funnel-Webs will channel venom into the fangs through the venom ducts right above them. Since the fangs are hollow, sometimes the venom will protrude as a glistening drop before the bite:



In some cases, Funnel-Webs have bitten down with such force that the venom drops were shaken off the fangs before impact, resulting in an unintentional dry bite! But don't expect to get that lucky.

So, that just about wraps it up for the Sydney Funnel-Web. As mentioned before, it has various relatives, but their coloration really isn't all that interesting, and they all look relatively similar, so it would seem like a real waste of time to show you a bunch of images of random Funnel-Webs. The only further note that I'll make here is that H. formidabilis (pictured mating above) has a venom that is even more lethal than that of the Sydney Funnel-Web, but bites are extremely rare because formidabilis tends to live deep in the forests of New South Wales, north of Sydney, and human contact with it is rare.

There is, however, a scientific debate concerning a potential second member of the Atrax genus, tentatively named A. murdoch, pictured below:



A. murdoch is native to Australia, but has spread rapidly upon introduction to the United States and Great Britain, infesting most American households and becoming endemic. Poisoning by A. murdoch is common, but often misdiagnosed. Symptoms tend to include rapid heart rate, increased blood pressure, paranoia and stupor.

For more information on Funnel-Webs in the Hexathelidae family, you can always visit Wikipedia.

No comments :