Christina was a Lycosa tarantula kept by Miles O'Brien in the 2360s as a pet. He found her on Titus IV, where he almost stepped on her. Though previously afraid of spiders, following an encounter with several Talarian hook spiders on a starbase at Zayra IV, his fear had diminished significantly, thereby enabling him to later make a pet of Christina.
In 2369, O'Brien introduced her to Reginald Barclay in Ten Forward, saying she wouldn't bite. While O'Brien got their drinks, he asked Barclay to watch her. The tarantula began to crawl up the lieutenant's arm, much to Barclay's displeasure. (TNG: "Realm Of Fear")