[header] How to identify a trapdoor spider [title] Take note of the spider's length. [step] Trapdoor spiders are approximately 0.79 in to 1.26 inches (1 to 3 cm) long. That means roughly between the size of your pinky nail and your thumbnail. 
[title] Look at the spider's body. [step] Trapdoor spiders are black or brown, with stout bodies and legs.