8

Chitinous Membranes and Analogous Material

119

Table 8.3 Comparison between Spider and Tasar Silk Moth (from various sources)

S. no Details

Spider

Silkmoth

1

Class

Order

Arachnida

Araneae

Insecta

Lepidoptera

2

Body segments Cephalothorax

Abdomen

Head

Thorax

Abdomen

3

Antennae

Absent

Present

4

Wings and

Wing venation

Absent

Parameter

Male

Female

Wingspan

16 cm

18 cm

Fore wing area

2121 mm²

2350 mm²

Hind wing area 1584 cm²

1850 cm²

5

Legs

Four pairs of legs and each leg is

composed of five segments

Three pairs of thoracic legs and each leg

is composed of five segments

6

Eyes

Four pairs on the top front area of

the cephalothorax

Ocelli are present

A pair of compound eyes on either side

of the head

Ocelli are absent

7

Silk characters

1. Strength—silk’s tensile strength

is comparable to that of high-grade

alloy steel (450–1970 Mpa)

2. Silks stretch up to five times to

their relaxed length without

breaking

3. Toughness—dragline silks have

a very high toughness which equals

that of commercial filaments

4. Temperature—dragline silks can

hold their strength below −40 °C

(−104 °F) and upto 220 °C (428

°F)

5. Super contraction—when

exposed to water, dragline silks

undergo super contraction,

shrinking up to 50% in length and

behaving like a weak rubber

6. Spider silk—average maximum

breaking stress (MPa) ranges from

710 to 1850

7. The primary structure is its

amino acid sequence, mainly

consisting of highly repetitive

glycine and alanine blocks. On a

secondary structure level, the short

side-chained alanine is mainly

found in the crystalline domains

(beta sheets) of the nanofibril, and

glycine is mostly found in the

so-called amorphous matrix

1. Elasticity is moderate to poor

2. Silkworm silk, therefore, has a linear

density of approximately 1 den

3. Silk is very elastic. It can stretch

10–20% without breaking

4. Silk is resistant to most mineral acids,

except for sulphuric acid

5. Silkworms were genetically altered to

express spider proteins and fibres

measured average maximum

6. Fibroin is made up of the amino acids

Gly-Ser-Gly-Ala-Gly-Ala and forms

beta-pleated sheets. Hydrogen bonds

form between chains, and side chains

form above and below the plane of the

hydrogen bond network. The high

proportion (50%) of glycine allows the

right packing. The addition of alanine

and serine makes the fibres strong and

resistant

(continued)