Why are female black widows so poisonous and aggressive;as compared to other spiders???

Question

Thanks for the extra bit o' detail...Tom Science 4

Answer 1

All spiders are venemous, some more so than others. The widow spiders can give a very painful bite which can be fatal. The black widow is one of the widow spiders, the redback in Australia is another. Widow spiders build webs and live in them with the females laying their eggs there. The males are much smaller and not dangerous. If you disturb a widow spider, she will bite you but she will not leave her web to do so.

With most spiders, the female is the larger and more deadly but with the Sydney funnel web spider, it is the male which is the most dangerous as it hunts for females in the breeding season. The funnel web is deadlier and more aggressive than the black widow or any other widow spider. It is also much larger.

Answer 2

Aggressive toward what? With respect to humans
black widows are relatively shy and non-aggressive
except occasionally when defending their egg sac.
They can be quite aggressive toward potential
prey. The notions that male black widows are
harmless and that they are normally eaten by the
female after mating are myths.

As to why they are so poisonous, who knows?
Most spiders are venomous, though one small
family, the Uloboridae, lacks venom. The venom
of most spiders is adapted to affect their normal
prey, and has little or no effect on a vertebrate
animal. There are only a few spiders whose venom has strong adverse effects on a human.
These include the black widows (which are not all
black), genus Latrodectus; the brown recluse
spiders, genus Loxosceles; the funnel-web
spiders of Australia, genus Atrax; and the sac
spider or ground spiders of South America, genus
Phoneutria. Possibly there are others, but there
is almost no information available on bites of most
kinds of spiders. Mortality rates from these bites,
among humans, are mostly very low. The highest
I have heard of is 2-5% from Latrodectus bites,
most deaths being of children or adults with
circulatory or respiratory problems. I don't know
what the mortality rates are for Atrax or Phoneutria.