The severity of the reaction to poisonous spider bites is dictated by many factors. The amount of venom injected may vary from almost none to a full dose, depending on the quantity of venom in reserve at the time of biting, the length of time the fangs are in the tissue and even the location of the bite. Additionally, the reaction of individuals to the same amount of the same type of venom may vary widely. Several hundred species of spiders occur in Missouri. Some of the more common groups include orb weaver, garden, cellar, crab, jumping, wolf and trapdoor spiders.
Tarantulas are very large specialized spiders that attract a lot of attention.
Some do occur in southern Missouri, but they are not very abundant. Only two Missouri species, the black widow and the brown recluse, are capable of causing a serious condition by injection of venom. Others may cause very minor irritation. Most spider bites occur without the victim being aware that it is happening. The female black widow is jet black with a red hourglass-shaped marking usually present on the underside of the abdomen.