Asp QueryStringParameter Conversion failed when converting the nvarchar

I get this error when I run the following code the global s are static int, I have looked at quite a few articles but cannot see where this is going wrong:

Exception Details: System.Data.SqlClient.SqlException: Conversion failed when converting the nvarchar value 'glb.catID' to data type int.

<asp:SqlDataSource ID="SqlDataSource1" runat="server" 
           ConnectionString="<%$ ConnectionStrings:CommerceConnectionString %>" 

           SelectCommand="select CategoryID, CategoryName, ProductImage,  Title,  SubCatID 
                          from Categories
                          JOIN Products
                          ON Categories.CategoryID= Products.CatID
                          WHERE CategoryID = @CategoryID AND SubCatID = @SubCatID ">
           <SelectParameters>
           <asp:QueryStringParameter Name="CategoryID"  QueryStringField="CategoryID" DefaultValue="glb.catID" /> 
           <asp:QueryStringParameter Name="SubCatID"  QueryStringField="SubCatID" DefaultValue="glb.subcatID"/>
           </SelectParameter