Hi Dear, Understanding your concern. As per your query you have symptoms of itchy blisters after a spider bite which seems to be due to infection by sting of bite venom. Need not to worry. I would suggest you to Apply little pressure on that area with cotton dipped in warm water to ooze out the pus properly. Apply betadine over area and clean that area properly with antimicrobial agent. Use of corticosteroid ointment is helpful. Take antibiotics orally to prevent further infection. Use calamine lotion on that to resolve itchiness. I would suggest you to visit dermatologist once to find out any hidden cause for your symptoms and get your other medical treatments postponed if its not a medical emergency. Hope your concern has been resolved. Best Wishes, Dr. Harry Maheshwari