What does a poisonous spider bite look like.?

Depends: This depends on the stage and severity of the bite. See http://www.Emedicinehealth.Com/spider_bite_brown_recluse_spider_bite/page11_em.Htm for pictures of the most severe bites and the spider and it's range. Please note that most bites do not reach these last stages! as for black widow bites, see http://www.Emedicinehealth.Com/black_widow_spider_bite/article_em.Htm.