A group of spiders is called a cluster or a clutter. A cluster is defined as similar things coming together to form a group.
The common collective names given to groups of animals are called the terms of venery or nouns of assembly and originate from hunting terminology used in England in the late Middle Ages. Many of the collective or plural names have been adapted to modern standard English terms and have perpetuated other group names that are both factual and humorous. A cluster is not only a group of spiders but also the collective noun for cats and antelope. A group of giraffes is a tower and a gathering of crows is called a murder.