It is always important to be able to recognize dangerous spiders and insects when you are camping or backpacking. In the United States of America the three most dangerous spiders are the Brown Recluse, Black Widow and Hobo spider. You can use the photos above to reference these spiders in case you ever come across them.
#1 The Brown Recluse:
The Brown Recluse utilizes necrotic venom to destroy the tissue of its victim. Brown recluse spiders are usually between .24inches and 0.79 inches in size, but may grow larger. While typically light to medium brown, they range in color from whitish to dark brown or blackish gray. There are important defining marking for the brown recluse on the dorsal side of their cephalothorax, with a black line coming from it that looks like a violin with the neck of the violin pointing towards the rear of the spider. Because of this violin design on the Brown Recluse, they are often times called by their nicknames the fiddle spider or violin spider. Brown recluse spiders build irregular shaped webs that frequently include a shelter for the spider. The brown recluse frequently builds its web in woodpiles, garages, closets, garages, cellars, sheds, shoes, dressers, and other man made area that receive little traffic and are sheltered from weather or direct sunlight. Unlike most web weaving spiders, the brown recluse spider will leave its web to hunt at night.
#2 The Black Widow:
The North American Black Widow spider (L. mactans, L. hesperus, and L. variolus) females are in most cases identified by a dark color and reddish hourglass shaped marking on their abdomen. The venomous bite of the black widow spider is considered particularly dangerous because of the neurotoxin latrotoxin, which causes the condition latrodectism. The bite can be very harmful to humans but is rarely fatal. The prevalence of sexual cannibalism, a behavior in which the female eats the male after mating, has inspired the name black widow spider. The black widow construct a web of irregular threads and will frequently hang upside down near the center of its web and waits for insects to become entangled. Black widow spiders tend not to be aggressive but can inflict harmful bites if disturbed.
#3 The Hobo Spider
The hobo spider constructs a funnel shaped web of silk sheeting and it lies in wait at the small end of the funnel for prey insects to become captured in their webs. Hobo spiders sometimes build their webs in or around human habitations. Hobo spiders have a light stripe running down the middle of the sternum and can sometimes be difficult to identify because of their similarity to other spiders in the United States. If examined closely, the abdomen has a v shaped or zig zag pattern down the center with the tip of the v pointing towards the head of the spider. The bite of the hobo spider can be very toxic to humans.
Information and photos found at Wikipedia and HikerCoupon.com