Q.
What is the most dangerous spider in the
world?
A.
It is hard to define which spider in the world is the most dangerous
to humans. Several spiders could qualify, depending on what you mean
by dangerous. Do you mean the spider with the most toxic venom,
measured by its effect on newborn mice or other mammals? Or do you
mean the spider that has caused the death of the most people? Those
that have the strongest venom may not be encountered
 by humans very
often, or may even have trouble piercing human skin and so are not
considered to be "dangerous". These include the Daddy Long
Legs, which people often say is the most dangerous or most poisonous but
in fact can't pierce a person's skin with its very small fangs. See
this page for further
info on the Daddy Long Legs. Data are usually only kept on bites from
spiders that are potentially deadly or cause severe reactions and
these data are not recorded consistently at a national or
international level. So to answer this question I will define dangerous as "deadly".
On current evidence the most dangerous spiders in the
world are Funnel-web spiders
 (Atrax and Hadronyche
species), Redback Spiders and their relations (Latrodectus
species), Banana Spiders (Phoneutria species) and Recluse
Spiders (Loxosceles species). In Australia, only male Sydney
Funnel Web Spiders and female Redback Spiders have caused human deaths, but
none have occurred since antivenoms were made available in 1981.
The Australian Funnel-web spiders are among the deadliest
spiders in the world in the effect their bites have on humans and
monkeys (although the bite has little effect on dogs and cats).
There are many species of funnel-web spiders in Australia but only
male Sydney Funnel-webs have caused human deaths. There have been only
13 deaths recorded from male Sydney Funnel-webs, but up to 30-40
people are bitten by funnel- web spiders each year. Mouse spiders may
have venom that is as toxic as that of some funnel-webs, as some
patients have had severe reactions to their bites, although no-one has
been recorded as having died from the effects of a mouse spider bite.
Antivenoms are available for both Funnel-web and Redback Spider bites.
A group of spiders that is dangerous in many countries belongs to
the genus Latrodectus in the Family Theridiidae. In Australia
we have the Redback Spider (Latrodectus hasselti). In
America, a common representative of this genus is the Black Widow (Latrodectus
mactans). Antivenoms are available for both Funnel-web and Redback Spider bites.
 A deadly spider which comes from South America is the
Banana Spider, Phoneutria species. In
south-eastern Brazil between 1970 and 1980, more than 7,000 people
were admitted to hospital with bites from this spider. An antivenom
also exists for this species. These are also called Brazilian
Wandering spiders and have been reported in bunches of bananas
imported into the United States.
 The Recluse or Fiddleback Spider is a deadly spider belonging to
the genus Loxosceles. Recluse spiders are found in many parts
of the world and have been introduced into Australia. The venom of
this spider can cause severe skin necrosis (eating away of the flesh)
and can be fatal although not many deaths have been recorded.
(Info - Australian Museum Online)
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