what's happened to this silkworm?

[Firewallx]

I am unsure of what is going on. A few have died today, but I am not sure of what. In the picture below, I can see something has come out of his rear. Does anyone know what may be wrong? They are fed mulberry leaves, and I rinse and dry them before giving it to them.

 

[kinyonga]

Could it be this?
http://www.wormspit.com/grasserie.htm

 

[Firewallx]

No, it's not grasserie. There aren't any bodily fluids leaking or swelling.
I probably should have mentioned that this silkworm is darker in color because its an early instar. My third instars usually have a lot of dark markings , and the head capsule is black until the fourth instar.
But thank you for taking the time to try and help me.