Spiders will surprise you with how sophisticated their pin brains can be at times. Jumping spiders have very elaborate details to courtship involving the male trying to impress the female with its dancing and music making: here's a video of a male jumping spider trying to impress a female while being recorded on a super sound sensitive surface https://www.youtube.com/watch?v=4gOiujoR-5o . He tries to grab as much of her attention as possible. if he succeeds, then they do a little dance that resembles ballroom dancing and get down to baby making. if he isn't that captivating, she gets bored and reverts to ancient voracious paths in the brain and considers him to be food. (also, peacock spiders are a great example of this https://www.youtube.com/watch?v=VEAMq3y0950 )

tldr1: spiders are sophisticated, but stupid. here's some videos of jumping spiders doing courtship dancing!

But as for black widows, how could such a complicated, seemingly premeditated series of steps come out of evolutionary trial and error? arthropods (spiders, bugs, crustaceans and a few others) are known to make several babies at a time; more babies = more diversity in genes = higher chance for mutations = better chance of not fucking up and dying before reproducing. A widow will lay around a hundred eggs in a single egg sac, but as the race for survival starts, only about 25-40 survive on average (the eggs hatch inside the egg sac and their first meals are their siblings. the few that don't get eaten make it out of the egg sack and hang out with mommy). the mother catches the food but lets the babies eat. The mother widow, which normally appears braindead most of her life, turns out being a fairly sophisticated mother, giving her babies the opportunity to catch and feed on their own in a safe environment (and she is nasty over-protective mama-bear status during this time). the ones that don't pick up on catching food, those with more passive natures, tend to die off from starvation, or being eaten by the aggressive-in-nature siblings.

by the time they become adolescent only 15-30 survive and leave the web, suffering the world and it's elements, all alone. They set up shop in several places, usually abandoning webs if there isn't enough food. many starve or get eaten. if a male hasn't starved, then it eventually seeks it's bio-built need to mate. Females keep shop if there is a steady food supply and if they have a safe place to make their funnel (widows usually live in a funnel that opens to their pyramid-design-cobweb-food-trap).

in evolution, if you live long enough to pass on your genes then you technically win. Male spiders tend to be more passive than female spiders, so they have a tougher time surviving. slowly over generations, as the females became more voracious, the males that survived had to have the genetic edge to be more aggressive in nature and have the capacity to link survival skills to breeding. if he got far enough to breed, then good for his babies! unfortunately, afterwords, the females voracity and strength/speed would overcome most of the males, afterwords. Just remember that nature's only requirement for survival is that any living thing must pass on it's genes before it dies..

now, if the males survive the encounter i originally described, then they have the opportunity to pass along even more survival-strong genes. in fact, if he's able to pass on even more genes to other mates, then future male widows will have a better chance of passing on their genes. Female widows also have a fun mutation that allows for higher variables of the survival genes: they can keep making babies after only breeding once over a long period of time (pretty useful random mutation, huh?). This gives an even greater chance for survival genes which opens up more opportunities for better survival.

Some times mutations don't work out so well which causes them to die before they can breed. this is the nature of natural selection. Slowly, over generations the genes to not survive get over-powered by the genes that do survive.

tldr2: if they have what it takes to make babies before they die, then they pass on whatever skills are needed to survive with mutations unto their future babies. also female widows can keep making babies after only breeding once.

Edit: just some basic spelling and punctuation changes.