Aciniform silks are manufactured by the aciniform gland, a structure that can de­scribed in the cob-weaver as somewhat “finger-like” shaped (Fig. 1.1). These silks are used for swathing prey, building sperm webs, web decorations, and egg sacs (Fig. 1.3).1 Partial cDNA sequences coding the major protein constituent, Acini­form Spidroin 1 (AcSp1), were initially reported, and more recently, the entire ge­netic blueprint for AcSp1 was completed.51 Aciniform silks have also been shown to be constituents of egg sacs and MS/MS analysis has demonstrated the presence of AcSp1 in egg sacs and prey wrapping silk.51b Inspection of the genomic DNA reveals the AcSp1 gene consists of a single exon that exceeds the largest exons reported from humans, chimpanzees, mouse, and zebrafish, predicting a protein size of 630 kDa. Analyzes of the 16 block repeats of L. hesperus AcSpl, which each com­prise 375 amino acids, show extreme conservation relative to block repeats reported from other spidroin family members.51c This represents approximately twice the size of the 200 amino acid block repeats reported for Argiope trifasciata AcSp1.51a Al­though the mechanical data available for aciniform silks is relatively scarce, stress — strain curves collected from a handful of orb-weaver spiders support that this fiber represents one of the toughest spider silk threads.51a Purified recombinant AcSp1 proteins from A. trifasciata carrying 2, 3, or 4 block repeats (denoted W2, W3, and W4) can be induced to form fiber-like threads by shear forces in physiological buf- fer.52 Mechanical analysis of hand-pulled, synthetic fibers produced from purified recombinant protein W4 have reported breaking stress and strain values of 116 ± 24 MPa and 0.37 ± 0.11, respectively.