Hello, If you are not sure if this is a tick bite or a spider bite and if it looks like a bullseye, then very likely this is a tick bite and you need to see your doctor soon and take antibiotics. Tick bites may cause Lyme disease so anytime a patient suspects he had a tick bite or has the bullseye lesion he should take antibiotics (doxycycline, or amoxicillin or cefuroxime, depending on the allergies a patient may have). Most of spider bites are nor dangerous and need no specific treatment except in few cases such as a black widow or brown recluse. The visit with the doctor will also determine if there is a chance that you have been bitten by one of these (depending on your symptoms and findings during examination). I hope this answers your query. I remain at your disposal for further medical assistance. Regards, Dr. Antoneta Zotaj General and Family Physician