The effects of spider bites on cats and dogs are similar to their effects on humans. Potential symptoms include redness, swelling, muscle pain or cramping, tremors, vomiting, diarrhea, blistering, or pain in the abdomen.  Dogs and cats rarely die from spider bites, but animals with compromised immune systems may suffer kidney damage. Vets also say that if your pet eats a spider, it's unlikely to cause any lasting issues. Still, if a spider bites your pet or your pet takes a bite out of a spider, monitor them closely for a few days and call the vet at the first sign of severe symptoms.