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.
There are over 40,000 species of spiders and 109 recorded families of spiders. Spiders are arachnids with eight legs. There's a little, rather interesting story below, about why they are called Arachnids.