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Posts tagged “Silk

Spider Egg Sac

12-10-12 spider egg sac3 IMG_6616As a result of many years of evolution, spiders have developed the use of different silks produced by seven glands for various functions (ballooning, webs, wrapping prey, dragline, egg sac, etc.).  The tubuliform gland is responsible for the large diameter silk fibers used in the construction of egg cases.  Unlike other silk glands, which synthesize protein throughout a spider’s lifetime, the tubuliform gland synthesizes silk for only a short time in a spider’s life, just before eggs are laid.  This silk is synthesized only by female spiders, and is the stiffest type of silk, which makes it a very protective covering for eggs. The pictured overwintering spider eggs had three layers of protection:  bark (the photo is of the underside of a piece of loose bark), an outer silk cocoon covering the egg sac and the egg sac itself – a tough layer of silk covering the eggs. (Reluctantly I opened the sac for the sake of an educational photograph, and did my best to re-wrap the eggs.)

Monarch Caterpillar’s Spinneret

Unlike spiders, whose spinnerets, or silk-spinning  spigots, are located at the tips of their abdomens, caterpillars’ spinnerets are located underneath their heads.  The most prominent white structure with a black band around it is the monarch caterpillar’s spinneret, in which its silk glands are located.  The smaller structures are called maxillary palps and are antennae-like sensory devices.  Prior to metamorphosing into a chrysalis/pupa, the monarch caterpillar draws silk through its spinneret, and forms a small, well-anchored button of silk. The caterpillar clasps this button with a structure called a cremaster, located at the tip of its abdomen, from which it suspends itself upside down.  Soon thereafter its skin splits, revealing a gold-dotted, green chrysalis from which an adult monarch butterfly will emerge in two weeks.