Do spider bites cause swelling

Dogs can definitely become swollen after being bitten by a spider. They can have the same allergic reactions to them that people do. If you think your dog has been bitten by a spider and is having an allergic reaction, you should contact your vet to see if it needs to be examined. Although, if the dog doesn't seem to be having any serious reactions (swollen tongue, throat, trouble breathing, etc.), you can give him Benadryl to relieve the itching and swelling caused by the allergic reaction.

The amount of Benadryl depends on the dogs weight and age, so you will need to call and ask your vet how much to give it.