I have a half-inch gap between the foundation of my garage and my
house. We're having some trouble with spiders, and have seen some
mouse-droppings so I'm trying to fill any cracks and crevices that may
be inviting to these pests.

What should I use to fill this? Is cement a good option or do I need
something that will allow this space to expand/contract with the
change in seasons? If I need something less rigid then what should I
use?

Here's a photo of the gap.

http://www.flickr.com/photos/31679241@N00/499608030

Thanks.