Some venomous spiders pack enough toxin in their bites to make a dog seriously ill or even kill him. It's important to recognize the signs and symptoms of a spider bite so that if your dog is bitten, you can get him to a veterinarian for immediate medical intervention.
A number of venomous spiders exist in the United States that can kill a human or non-human animal, though very few species of spider are equipped with the fangs and strength to penetrate a dog's thick skin. The black widow, the brown widow and the brown recluse spiders, however, all possess that ability. If you have dogs, it would be wise to find out if these spiders are indigenous to your area and, if they are, to become adept at identifying them.
The difference between a sign and a symptom is one is objective and one is subjective. A sign is something an observer can see, whereas a symptom is felt by the victim. Signs of a spider bite on a dog include swelling at the site of the bite. The eyelids, earflaps, nose and lips are vulnerable places on a dog because they are not covered by a thick coat of fur and their tissue is thinner than on other parts of the body. You may notice the dog having difficulty breathing if the bite is on his nose. If the bite occurred in an area that is not covered by fur, you'll see redness, swelling and indications of pain (the dog licking at the affected area, for example) almost immediately. You may even be able to see the bite's puncture marks.
The symptoms will vary from dog to dog and depend on the potency of the venom. The first symptom will likely be a sharp pain at the location of the bite, followed later by fever, weakness, and muscle and joint tremors and pain.
As the neurotoxin progresses through the dog's body, you'll notice him growing increasingly excited and anxious. His muscles may become rigid, and he might vocalize loudly in response to the severe pain in his back, chest and abdomen. The dog may show a lack of coordination and be unable to stand. He may also experience increased blood pressure and heart rate, respiratory collapse due to abdominal muscle paralysis, and seizures. Death can result if the dog is not quickly given anti-venom treatment.