Usambara orange tarantula Pterinochilus sp. rises up on rear legs and bears fangs in typical tarantula threat posture. These spiders are among the most aggressive tarantulas in the world and are indigenous to the arid Usambara region of Africa. They can attain a legspan of 12.5 cm which makes them one of the largest Old World tarantulas, though not as large as some New World giants.