THAT IS A FLEA, FOR SURE!!! I am just getting rid of a flea infestation. Three months of fighting them! I hadn't seen a flea in nearly 20 years and BAM, fleas! I am told the same by many, hadn't had fleas in years and now they have them. We had no winter last year, that's why I suppose they were so bad this year. My dogs were on Frontline for the summer but I have never used flea meds on my cats because they don't go outside. It always worked, until now.
Treat the dogs and cat and wash all their bedding, vacuum frequently and throw out the bag. Good luck.