Thats sad to see. Even if they were normals it would still be heart breaking. At first I was thinking this could have been caused by high temps but from your other post you stated they were at 88 degrees with a helix so there is very little chance there.

The only other thing I could think is perhaps the spider gene mixed with an unknown gene in your normal parent proved fatal? Perhaps you should breed that female to something else next season.

I wish you luck in the future!

Richard