The fronds and compound tendrils of the Stephanian (Late Carboniferous) seed fern Blanzyopteris praedentata possess several types of trichomes, two of which may, based on their morphology, have functioned as deterrents against herbivores. Bands of upwardly curved trichomes, occurring on the adaxial surfaces of tendrils, frond- and pinna rachides, are also known from extant plants, where they create mechanical obstacles. Other trichomes that are glandular occur on most parts of the foliage and tendrils and represent a different form of defence mechanism. These trichomes apparently possessed a touch-sensitive mechanism that opened the secretory cell when touched. They are interpreted as functionally similar to the so-called ‘explosive’ trichomes of certain extant Cucurbitaceae and Solanaceae. Studies of living Oleander aphids (Aphis nerii) on Sicana odorifera (Cucurbitaceae) demonstrate the effectiveness of the physical component of this defence. When touched and ruptured by an aphid, the trichomes of S. odorifera rapidly release a sticky exudate, which adheres to the animal's legs; the accumulation of exudate on the legs eventually impedes the aphid. Based on these studies, hypotheses are presented on the types of animals that might have been deterred by the glandular trichomes of B. praedentata in the Late Carboniferous. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 133–149.