“How does a spider gene get into goat milk in the first place? Nexia uses two common spider specimens, Araneus diadematus (the common garden spider) and Nephila clavipes (the golden orb weaver, native to many tropical forests). The spiders are frozen in liquid nitrogen, then ground into a brown powder. Since every cell of a spider contains the precious silk-producing genes, it’s easy to extract them. These genes are then tested in the”Charlotte machine,” what Turner calls a ”synthetic goat” that tests whether or not the gene will function inside an actual goat.
Next, the gene is altered. A ”genetic switch” is added, which programs the gene to ”turn on” only inside the mammary gland of its new female host during lactation. The altered gene is then pushed on a fine glass pipette into a goat egg. The baby goat will have a spider gene present in each of its cells (its eyes, ears and hooves will all be part spider), but only in the mammary glands of female goats will the silk gene actually spring to life. The goat will eventually start lactating a kind of silk-milk mixture, which looks and tastes just like normal milk. This milk is first skimmed of fat, and salt is added to make the silk proteins curdle into thin whitish particles that promptly sink to the bottom. After the residue has been removed from the milk, a little water is added to this sediment until it turns into a golden-tinged syrup. This silk concentrate is known to scientists as ”spin dope” and is more or less identical to what is inside a spider’s belly. Now completely stripped from its milky context, the syrupy raw silk is ready for spinning.”