I have a couple of red mason bee nest tubes in my garden and they have been very successful in attracting these insects, but unfortunately the cardboard tubes need replacing every year or two. This winter I have improvised and used stems from a Himalayan honeysuckle. This invasive non-native species which colonised our garden from a neighbours is attractive to bumblebees (for pollen) and birds (which eat the fruit) and so has been left to grow. The stems however were coppiced this winter, and were found to be hollow with partitions at each node. I have cut them into sections with a node at one end, and used them to replace the worn out cardboard tubes. The result is a mixture of different sized cavities, which should attract a wider range of bee species.