places like lowe's and home depot carry a mulch that is make from recycled tires, it's rubber mulch. but it looks just like wood mulch, that would be an option. you could also use straw or shredded leaves, not sure how good the straw would look for landscaping, does good for veg. gardens though.

Thanks, but now I'm reading that it's not the mulch itself that they feed on, but rather the moisture that allows them to reside there allowing easier access to the wood nearby. So unfortunately looks like I'm going to leave it empty for now, wish there were a better solution.