[Matthew]

Matthew asked the Naked Scientists:

Is the poison of the deadliest spider worse than the deadliest snake?

What do you think?

[grumpy old mare]

Well - is there an antidote to spider poison like there is for snake poison?

[RD]

the inland taipan, has the most toxic venom of any land species worldwide, although it is not the most deadly.

http://en.wikipedia.org/wiki/Taipan

This would suggest that taipan (snake) venom is more toxic than any spider venom.

Note: "most toxic venom" does not necessarily mean "most deadly" (kills most number of humans),
another snake species could be less toxic, but more numerous, so kill more humans, i.e. more deadly.

[LeeE]

Hmm... there seem to be a few different LD50 ratings around.  Wikipedia give an LD50 dose from the Beaked Sea Snake as 0.02 (mg/kg) - the Inland Tiapan LD50 dose is 0.03 (mg/kg).  However, the LD50 dose of Batrachotoxin from the poison dart frog is estimated to be 0.002-0.007 (mg/kg).

Other sources give higher LD50 quantites for the Beaked Sea Snake, making it less venomous than the Tiapan, but I was lead to believe that the sea snakes needed more powerful venom than land snakes due to sea water entering the puncture.

Box jellyfish are regarded as the most venomous animals in the world and have killed around 5000 people in the last 50 years but it's not clear if that's mostly due to the amount of venom they release or it's strength.

[RD]

the inland taipan, has the most toxic venom of any land species worldwide, although it is not the most deadly.

http://en.wikipedia.org/wiki/Taipan

This would suggest that taipan (snake) venom is more toxic than any spider venom.

"land species" includes spiders but not sea snakes, also frogs are not mentioned in the original question (is frog toxin "venom"?).
Got any LD50 stats on spider venom Leee?

[LeeE]

The question didn't specifically refer to land species and sea snakes are still snakes.  I don't know if the frog toxin could be classed as venom because it's not transferred by biting but is secreted by the skin.  I just thought it was an interesting comparison with the LD50 ratings from the snakes.  The Box Jelly toxin is regarded as a venom, but that's not delivered by a bite either, so I don't know how a venom should be defined - I'll stand out on that one.

Couldn't find any LD50 stats on spider venoms - I'd be interested to see some though.  I imagine that it must be more difficult to get enough spider venom to run the tests though.

[RD]

The lethal dose of the black widow venom is reported as an LD50 of 0.0009 mg venom / gram body weight (mouse).
LD50 is a standardized amount representing the dose required to kill 50% of the experimental animals.

http://kaston.transy.edu/widow.html

Black widow spider ... The venom is more toxic than most snake venoms, with an LD50 of 0.9 mg/kg in a mouse.

http://books.google.co.uk/books?id=C8xJE2NfQpIC&pg=PA268&lpg=PA268&dq=ld50+%22black+widow+spider%22&source=web&ots=Cu8-Jr6-0s&sig=EyYHVvOyAU21C_-kws6xoqYN19I&hl=en&sa=X&oi=book_result&resnum=9&ct=result

The LD50 of the black widow venom (L. mactans) is 1.39 mg/kg.

http://linkinghub.elsevier.com/retrieve/pii/S1096286706000648

'Yellow Scorpion', Leiurus quinquestraitus produces one of the most potent venoms of all scorpions.
It has an LD50 of about 0.3 mg venom/kg mouse

http://www.vency.com/poisonousanimals.html
Scorpions, like spiders, are arachnids.

They all seem to have a very similar LD50 of around 1mg/Kg.