Where are the specialized barbed hairs that cause significant irritation located on the tarantula?

On the spider's abdomen

The defensive hairs that tarantulas can dislodge when agitated or threatened are specifically situated on the lower part of their body structure, known as the abdomen. When stressed, the spider employs its hind legs to kick these barbed hairs backward toward the source of irritation. Once these microscopic projectiles embed themselves into the attacker's skin, they initiate a cascade of irritation, itching, and sometimes rashes. This anatomical placement allows the spider to deploy them as a projectile defense mechanism without requiring direct physical contact using its fangs or mouthparts, provided the threat is within range of its kicking motion.