Glochid
Glochids or glochidia (singular "glochidium") are hair-like spines or short prickles, generally barbed, found on the areoles of cacti in the sub-family Opuntioideae. Cactus glochids easily detach from the plant and lodge in the skin, causing irritation upon contact. The tufts of glochids in the areoles nearly cover the stem surfaces of some cactus species, each tuft containing hundreds of glochids; this may be in addition to, or instead of, the larger, more conspicuous cactus spines, which do not readily detach and are not generally barbed. Mechanical irritant dermatitis Reaction to the glochidia Most cacti possess spines, some large enough to cause serious wounds. Glochids however, though smaller, commonly induce more troublesome, more persistent, dermatological manifestations in humans. Though minute, glochids commonly are barbed and once they have penetrated the skin barbed glochids are practically impossible to dislodge without leaving scraps of foreign material in the wound. Implantation of glochidia in the skin does sometimes cause immediate irritation, but not always, as one may deduce from the presentation of patients with granulomatous lesions around glochidia, patients who have no recollection of the penetration that caused the acute injury, even when it is clear that the injury is far from fresh.