Sitting on couch and had a spider crawling on arm and it was very small but looked like brown recluse. how do ik if it bit me?

Brown recluse bite: Brown recluse spider bites often go unnoticed initially because they are usually painless bites. Occasionally, some minor burning that feels like a bee sting is noticed at the time of the bite. Symptoms usually develop two to eight hours after a bite and include itching at the site of the bite, nausea, vomiting, fever, and muscle pains. Immediate medical attention is recommended.

Severe reaction: It should be pretty obvious, because the bite causes a nasty reaction. The skin may turn black at and near the bite.