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When The Male *is* Deadlier Than The Female

by Martin Overton


This article was created to offer some clarification to the 'Did You Know ...' entry in last weeks edition. (Arachnids Weekly Vol1. No.10)

I have spent a fair bit of time over the last week scouring the web and re-reading some of my arachnid books to try and get to the bottom of this issue, and I believe the information presented here clearly shows that the Male of the species (Atrax robustus) is clearly the culprit of all the bites reported. The female, although venomous is *not* considered a threat to humans.

The first good web source I found was: http://www.emedicine.com/EMERG/topic548.htm

Authored by Simon G. A. Brown, M.D., Staff Specialist, Department of Emergency Medicine, Royal Hobart Hospital

He states:

"Bites from these spiders are remarkable in two respects. Firstly, the venom affects man and monkeys far more than other creatures. Second, only the bite from the *male* appears to be dangerous, a reversal of the situation with other highly poisonous spiders. Venom toxicity is consistently several times higher in the male than the female and the male behaviour pattern of permanently leaving the burrow to seek a mate leads it to enter houses and find it's way into clothing and bedding."

He continues...

"Funnel web spiders are restricted to the eastern and southern regions of Australia. The distribution of the Sydney funnel web (Atrax robustus) centers on the greater Sydney area, extending north to the Hunter River, south to the Shoalhaven River and westwards to Lithgow. Hadronyche spp. have a much wider distribution from south east Queensland to Victoria, Tasmania and parts of South Australia. To date, serious envenomations have been reported only from the Sydney-Newcastle-Illawarra region, however all funnel web bites must be treated with caution.

It has been estimated that 30-40 cases of funnel web spider bite occur each year in eastern and southern Australia but only a small number (perhaps 1 in 10) require treatment with antivenom.

Mortality/Morbidity: Fatalities have only been recorded following bites by Atrax robustus. The death rate is difficult to determine from data from the pre-antivenom era. Between 1927 and 1980, 13 deaths attributed to Atrax robustus were reported in the medical literature and news media. Severe envenomation, but not death, has been reported following bites by Hadronyche spp.

Death occurs between 15 minutes and 3 days. Children tend to die earlier from pulmonary edema, whereas adults tend to die later from persistent hypotension or other complications."

Another Source at: http://www.sci.uts.edu.au/depts/hs/SpidersRes.html

States....

"Many contain lethal neurotoxins but the 14 human fatalities, recorded since 1927, following envenomation have all been attributed to the *male* Sydney funnel-web spider Atrax robustus. Fortunately, following the introduction of an antivenom in late 1980 no new fatalities have been attributed to the bite of this group of spiders. Dr Nicholson maintains a colony of Blue mountains funnel-web (Hadronyche versuta) and Sydney funnel-web (Atrax robustus) spiders which are regularly milked for their venom. Milking is achieved by the use of a Pasteur pipette connected to a vacuum pump to remove the venom which collects at the end of the chelicerae."

Conclusion:

I believe that this clearly shows that although the female of Atrax robustus is venomous (estimates vary from a quarter to a sixth of the males potency) there are no substantiated bites from females of this species, due mainly to the fact that the female doesn't come into contact with humans as often as the males.

During the breeding season the males are often responsible for biting innocent humans, as they are very aggressive and tend to attack at the slightest provocation whilst looking for a mate.

[Of course if I haven't convinced you or you have data that counters my arguments then feel free to reply.]


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