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, like most living creatures, are assigned to ranks in what is called a taxonomic hierarchy. Creatures with similar physical characteristics and/or genetic traits are placed alongside one another in each rank. Here is how a thin-legged wolf spider is placed, for example (and yes, spiders are animals):