where did cluster lizards come from?

So a summery of all the ideas you mentioned(and a few of my own) is this:

The cluster lizards were parsites in the giga-shadow (posibly symbioticly).
When it burrowed in to the cluster planet they got out and people thought they lived in the cluster.

And the web may be a subspecies of a race the insects fear (never a good thing for humans!)

I hope I summed that up correctly.