Poisoning by spiders' bites and scorpions' stings domestic canines and felines seems to be frequent, considering the biology and behavior of these animals. However, little is known about this relationship. In the present review, we compiled the available information concerning this topic by focusing on arachnids that can cause accidents, reported cases in the scientific literature, and epidemiological and clinical aspects of accidents with domestic canines and felines. Arachnids of medical importance are distributed worldwide, but the cases described in the literature are episodic, and some report animals' death. Each taxon has specific venom toxicity that can affect organisms differently. Thus, the diagnosis and clinical treatment must be based on the individual that caused the accident. Knowledge on the occurrence of arachnids of medical importance, their biology, and venom toxicity must be deepened and publicized to avoid accidents.