My 2 Y/o Son Has What Appears To Be A

My 2 y/o son has what appears to be a bug bite on top of his head. We noticed ot this morning dropping him off for daycare. Upon picking him up, we noticed a swollen line from bite down his head about 4 inches. (phlebitis?). He exhibits no other symptoms, no fever or behavior change. It does not hurt or itch. Does this warrant an ER visit? as it is too late for an after hours clinic.