What was the source of the mutation?
Considering that spiders were matriarchal, female spiders had an extremely high status and could mate with any male spider they wanted. Luo Su speculated that the massive female orb-weaver spider in the mine had the highest chance of being the leader of the spiders.
But being the leader didn't mean being the source of the mutations. Although the massive orb-weaver spider could mate with any male spider it wanted, just like the others, its mutations had been caused by the chemicals.
It could not be the source of the mutations!
As he thought about it more, he suddenly found a plothole. The chemical caused the spiders to mutate and rapidly grow larger in size, so why did it not have any effect on other insects?
If you said that it was because spiders were arachnids and not actually insects, then why didn't scorpions or centipedes mutate?