Large spiders with legs half a metre long, twenty of which Miles O'Brien once had to crawl past in a Jefferies tube, curing his lifelong fear of spiders.
Talarian hook spiders are large arachnids whose legs reach half a metre in length.
They are described in the episode Realm of Fear, when Lieutenant Barclay confesses his terror of the transporter. O'Brien answers with a story of his own: he used to be afraid of spiders, until a repair job at the starbase on Zayra IV obliged him to crawl through a Jefferies tube occupied by twenty Talarian hook spiders in order to reach a damaged emitter array. He got through, and the fear never returned.
By the end of the episode O'Brien is showing off his pet tarantula Christina, found on Titus IV, and Barclay lets her walk across his arm, a small sign of how far he has come.