Spider Bites By Robert A Barish, MD, MBA, University of Illinois at Chicago; Thomas Arnold, MD, Department of Emergency Medicine, LSU Health Sciences Center Shreveport Reviewed / Revised Jan 2022 | Modified Sep 2022 View Patient Education Symptoms and Signs Diagnosis Treatment Key Points Topic Resources Brown Recluse Spider Bite Black Widow Spider Brown Recluse Spider Disorders That Mimic Spider... Almost all of the 40, 000 species of spiders are venomous.