[Hermes]

Did Sam Verner summon the bugs, or did the bugs find a way to our world on their own?

Okay, if you guys say I should read "Find your own truth" I will.

[Mirikon]

Twist did not summon the bugs. Yes, you should read "Find your own Truth".

As for Twist, he led the Ghost Dance to weaken Spider, one of those totems that seems to be on the line between normal totem and insect spirit. And Spider's servants were already loose when he did this, though many of them bit it during the ritual, which also nullified a bunch of nukes.

As for the bugs in general, it is thought that the husband of the founder of the Universal Brotherhood was the first insect shaman. How he heard that call is anyone's guess. But if you want to know more about that, read the Universal Brotherhood - Missing Blood book.

[CanRay]

A Ghost Dance...  One of many possibilities. 

[BreederofPuppets]

An interesting possibility: Spider, an evil totem for sure, also keep the insect totems and their spirits in check, away from earth (or reality, material world, whatever).  By weakening Spider, Twist inadvertently allowed the Insect Totems to contact possible shamans on this side of the veil. 

This (my post) would better be discussed, however, over in the Secret History section.