While most stings are painful, they are not dangerous unless your dog suffers from an allergic reaction. Such allergic reactions are rare but they can cause constriction of the dog's airways, resulting in an inability to breathe.
Swelling of the skin is a sign that your dog has been stung. If your dog has an allergic reaction to the sting, you will also see swelling around the dog's face or legs. The swollen areas will feel hot to the touch.
If your dog is stung by a bee or other type of insect that leaves its stinger behind, use tweezers to pull the foreign body out of your dog's skin. Be sure to grasp the stinger at the point of entry, and to pull it straight out of the skin. Do not grasp the upper part of the stinger with the tweezers because this can result in the injection of more venom into the area. Once the stinger has been removed, apply a cold compress to the spot. Try to keep your dog quiet, and observe it for any distress or for the allergy symptoms mentioned above. If the dog appears uncomfortable, take it to a veterinarian immediately, since allergic shock can occur within half an hour.
Insect bites are usually more painful than dangerous with the exception of the black widow spider, whose venom is more potent than a rattlesnake. If you suspect your dog has been bitten by a black widow, wrap the dog so it cannot easily move and take it to a veterinarian immediately. Call first to ensure that the antivenin needed to treat black widow bites is available.