I created a new world for 1.9, using the large biome world type, and have spawned in a Plains Biome - the only other biomes in the vicinity are a river and forest biome. Near where I spawned is a village, which I have been adding onto for a few weeks.

Last week I built a large cobblestone structure, and I placed each foundation block (I didn't use any existing stone for the foundation). Today I mined out some of the foundation, and there was a Silverfish in it. Before I could kill it, it infected the surrounding cobblestone, and spawned more silverfish - before I was able to burn them all to death, they broke most of my foundation blocks and about half of the foundation blocks for the houses in the village (and I'm pretty sure the blocks not missing are now monster eggs).

I checked with an Eye of Ender - there is no Stronghold in the area. The Village is at normal, above ground height, and exists solely in a plains biome - there is no Extreme Hills, and there are no Igloos

Seed is -586314636804796594
Coordinates of the village are 308.71.56
My local difficulty if 2.02 / Day 28 (Normal difficulty)