My son has 4 ant bites on his ankle from yesterday morning. tonight it's still swollen and red. he scratched them and now they are open blisters?

Possible infection : Any insect bite, no matter what the bug, has the potential to get infected, as there is a break in the normal skin integrity. Add scratching to the mix and even more risk of the area getting infected. Wash area well with antibacterial soap, apply a topical antibiotic cream, and if not getting better in a few days or if worsening or fever, have your primary care doctor check things out.