Goliath bird-eating tarantulas are the largest spiders by mass in the world (the giant huntsman spider has a larger leg span), belonging to the genus Theraphosa. They can have a body length of 5.1 inches and a leg span of a foot. At the time I started keeping tarantulas in the late 1970s, there was only one species known, Theraphosa blondi (though at the time it was being sold as Theraphosa leblondi). Blondi, described in 1804, was thought to be the only species of goliath until in 1991, the goliath pink foot (Theraphosa apophysis), was described. Then, in 2010, the burgundy goliath (Theraphosa stirmi) was described. Though all three species look similar as adults, the spiderling and juvenile stages show the greatest differences between species.