Ready to Molt

When doing the spood check today, I noticed that Incy Wincy was finally showing signs of an impending molt. Since I got him, he has been scraggly looking. His abdomen was pink and bald where he had kicked off all of his hairs, presumably through the stress of being posted - Incy Wincy is a very skittish spider, and runs for cover at the slightest movement so he is very prone to kicking hairs. Once he has molted, his abdomen should be nice and fluffy again. I can't wait to see that.

Spiders (and other invertebrates!) molt through a process called Ecdysis, and while most insects will hang upside down to molt, spiders lay on their backs. The external skin or exoskeleton is the top layer of two, and is also known as the cuticle. Underneath the cuticle is a layer of epidermal "skin" cells. When getting ready to molt, glands in the epidermal layer secrete a hormone to separate the two layers. This hormone contains enzymes which - when active - will digest the inner layers of the old exoskeleton, allowing it to be shed. This stage can be seen in Incy's picture, as it makes their abdomen appear shiny and darker in colour as the top layer separates from the epidermis.

Once the two layers are loosened, the epidermal cells secrete a fresh layer of cuticle, underneath the hormone layer. This will become the new exoskeleton. As the new layer of cuticle is created, the digestive enzymes in the hormone layer will start to digest the lower layers of the old cuticle. This thins it down, making it easier for the spider to shed, and then reabsorbs into the spiders body.

Once the fluid is reabsorbed and the old cuticle is thinned, the spider increases the haemolytic pressure in it's body, allowing it to surge and crack the outer layer. It can then climb out of the old shell.

The new shell will remain soft and pliable for several hours (or days depending on the spider size!) allowing for the spider to pump fluid into the spaces and expand the shell before it hardens. This is how they grow. During this time, they are very vulnerable - their exoskeleton is soft leaving them prone to injuries or predation.
Every part of the spider molts, from their book mlungs, their reproductive parts, and their fangs. I don't feed my spiders for several days after their molt because, even though they are clearly hungry, their fangs are also soft and any attempt to feed could damage the fangs irreparably until the next molt.