A fully executed contract date begins once both parties signed it. In your case, since you signed them first, the date begins when the seller/affixes his signature. However, the delivery of the ratified contract should also be considered. Consult your realtor and a lawyer.
A group of spiders is called a cluster or clutter. Spiders belong to the group of animals called arachnids.
Spiders of the genus Steatoda (also of the Theridiidae family) are often mistaken for widow spiders, and are known as  false widow spiders ; they are significantly less harmful to humans.