Calamistrum
Calamistrum[edit | edit source]
The calamistrum is a specialized anatomical structure found in certain species of spiders, particularly those belonging to the family Amphinectidae and Dictynidae. This structure plays a crucial role in the production and manipulation of silk, which is essential for various behaviors such as web construction, prey capture, and reproduction.
Anatomy and Function[edit | edit source]
The calamistrum is located on the metatarsus of the fourth pair of legs in spiders that possess it. It consists of a row of curved, bristle-like setae that are used in conjunction with the cribellum, another silk-spinning organ. The cribellum is a plate-like structure located in front of the spinnerets, and it produces a unique type of silk that is extremely fine and woolly in texture.
When a spider uses its calamistrum, it combs the cribellate silk, causing it to fray and form a mat of fine fibers. This process is known as "combing" and is essential for creating the characteristic woolly silk that is used in the construction of cribellate webs. These webs are non-sticky but highly effective at entangling prey due to the fine, tangled nature of the silk.
Evolutionary Significance[edit | edit source]
The presence of a calamistrum and cribellum is considered a primitive trait among spiders, suggesting that these structures were present in early spider ancestors. Over time, many spider lineages have lost the cribellum and calamistrum, evolving instead to produce sticky silk using their spinnerets. However, the retention of these structures in certain families indicates their continued evolutionary advantage in specific ecological niches.
Ecological Role[edit | edit source]
Spiders with a calamistrum and cribellum often occupy ecological roles that differ from those of their sticky-silk-producing relatives. The woolly silk produced by these spiders is particularly effective in dry environments where sticky silk might lose its adhesive properties. Additionally, the unique structure of cribellate webs allows these spiders to capture a wide range of prey, including insects that might otherwise escape from sticky webs.
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