Ontogenetic changes in cribellum spigot number and cribellar prey capture thread stickiness in the spider family Uloboridae.
Opell B.D.
Uloborids produce dry cribellar prey capture thread whose surface is formed of thousands of fine, looped fibrils. These fibrils are spun from spigots on an oval spinning plate termed the cribellum and handled by a setal comb on the fourth leg termed the calamistrum. Ontogenetic studies of the triangle-web species Hyptiotes cavatus and the simple-web species Miagrammopes animotus show that increases in the number of cribellar spinning spigots are associated with increases in the stickiness of cribellar threads. For H. cavatus this relationship is similar to that determined by a previous interspecific comparison. Relative to cribellum spigot number, M. animotus produces stickier threads than does H. cavatus. Differences in the features of these species' cribellar fibrils do not explain difference in thread stickiness. Cribellar threads produced by M. animotus have shorter, wider puffs than those produced by H. cavatus and, consequently, achieve a greater contact surface area per mm of length than do threads produced by H. cavatus. The more closely spaced cribellum spigots of M. animotus maximize the number of fibrils that contact a surface. Miagrammopes animotus also has a longer calamistrum and more closely spaced calamistrum setae than does H. cavatus. This demonstrates how small differences in spinning anatomy and behavior can fine-tune the physical characteristics of cribellar threads in ways that maximize their stickiness.
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