Research

I have been doing a bunch of research on spiders, and the consensus seems to be that Black Widows are the most dangerous, yet common in the American South all the way up to Canada. This makes my story somewhat realistic. I've also been trying to figure out common symptoms of a spider bite. According to my research, here are a few:

-sometimes victim will experience pain at site of bit, but danger is that they may not
-abdominal pains
-sore muscles, especially feet
-dry mouth
-paralyzed diaphragm
-excessive sweating
-swollen eyelids
-difficulty breathing

According to this article, the victim is usually given anti-venom or calcium gluconate.
Source: www.badspiderbites.com/black-widow-spider.php

About Black Widow Spiders:

-most common poisonous spider bite in the United States
-spins irregular web in crevices/dark places
-long legs with dark black bodies, female has distinctive red hourglass-shape marking on abdomen
-female is poisonous, male is not
-local pain and swelling at sit of bite, pain maximizes after 1-3 hours
-bites can be fatal, but less than 1% result in death

Source: http://nd.essortment.com/poisonousspider_rlpt.htm

More specific symptoms of BW spider bite:

-four species of Black Widows, all have strong venom
-bite is not always felt, but when it is, feels like a pin prick
-initial pain dissapears rapidly leaving a local swelling and two tiny red spots that appear at site
-muscular cramps in shoulder, thigh and back usually begin within 15 minutes to three hours
-severe cases cause pain spreads to abdomen, blood pressure rises, there is nausea and exessive sweating, as well as difficulty breathing
-death may result depending on the victim's age, physical condition and location of the bite

Physical appearence of BW spider:

-Southern BW spider: shiny, jet black color w/ red hourglass marking on underside of abdomen and another resd spot at tip end of abdomen
-Northern BW spider: row of red spots located in the middle of the back and two reddish triangles located on underside of abdomen, resembling hourglass
-Southern BW is the most widespread widow spider in southern states and is found as far north as Massachusetts
-found outdoors in places such as stumps, wood piles, rodent burrows and storm sewers

Source: http://woodypest.ifas.ufl.edu/spider.htm