The venomous arthropods discussed in this handbook were selected for inclusion due to the relative severity of their envenomizations and/or the high frequency of their contact with humans. It should be stressed that other arthropods found in the United States are capable of producing envenomization reactions in humans. Regardless, all venomous arthropods found in the United States can be categorized under one of the three types of envenomization methods described in this handbook: (1) biting/piercing, (2) stinging, and (3) urticating/vesicating. The biting/piercing arthropods inject a toxin through an apparatus associated with or near their mouthparts; and the stinging arthropods, through a stinger located at the posterior end of the abdomen. Urticating and vesicating arthropods are grouped together because they both release their toxins on contact. They differ in that the urticating arthropods usually release their toxin through venomous hairs; and vesicating arthropods carry a toxic substance within their system, which is released through small body openings. To facilitate the utilization of this handbook, each venomous arthropod presentation has been organized into the following information categories: • Identification. Bringing the arthropod causing an envenomization to the medical facility treating the victim is most helpful. In most cases, an identification must be made before the proper form of treatment can be determined. To assist personnel with identification, the key characteristics and representative color photographs are provided for the venomous arthropods discussed. • Distribution. Most arthropod envenomizations occur during the warm plant-growing season when venomous arthropods are most numerous. Since the Southern United States has the longest growing season, venomous arthropods are abundant for a longer period of time in this region. Also, the moderate climate of the Southern States, with fewer weather extremes, permits a greater variety of venomous arthropods to survive, propagate, and produce multiple generations each year. Specific regional occurrences are indicated. • Biology/Behavior. Pertinent biological information is provided to help increase the reader’s awareness and understanding of venomous arthropods. These factors are essential in developing a good avoidance and control program. • Avoidance/Control. To assist in preventing envenomization accidents, several means of avoidance are listed for each venomous arthropod. Since the status of insecticide recommendations is constantly changing, few specific recommendations are included. When insecticide control is necessary, an Air Force, County Extension Service, or United States Department of Agriculture entomologist should be consulted for current recommendations. Any insecticide must be applied according to the instructions on the container label.