Birds are not the only creatures attracted to nest boxes: spiders, woodlice, beetles and all manner of other creepy crawlies take refuge there, often making it their winter home. The mossy or grassy remains of nests offer additional insulation and protection from the weather. And it is not only birds that make their nests inside a handy box: bumblebees, especially the Tree Bumblebee, Bombus hypnorum, (left) are well known nest box colonisers. This bumblebee is a relatively recent arrival, which was first recorded in 2001 in Wiltshire. It has since become quite widespread and is common at Exbury.
When a colleague and I were cleaning out the nest boxes on Jubilee Hill in January we came upon something I had not seen before. Attached to the underside of the lid of three of the boxes was a dense, sticky mass filling about a third to one half of the box (right). It was extremely difficult to detach and I had to use a screwdriver to pry it off. Once off, it was still hard to pull it apart. It resembled a dense soft felty cloth, but I noticed that it seemed to have tunnels running through it and after a while we found maggots inside the tunnels.
After a bit of investigation I discovered that the nest boxes had indeed been taken over by tree bumblebees, which in turn had been predated by something called a Bee Moth (Aphomia sociella) (left). This is a small olive grey moth, with a pinkish area on its forewings, sometimes confused with Wax Moths, a serious pest of beehives. Bee moths lay their eggs in a web and feed on nest material and other detritus. When the larvae have developed fully they feed on the wax cells where the bumblebee's own larvae are developing, but do not usually destroy the entire brood. There is not much that can be done to deter them, but I hope that clearing them out and disposing of their nests will reduce the population somewhat, and allow the bees to breed successfully. One possible benefit might be to provide a winter larder for the blue tits. A pair was scolding angrily as we cleaned out the boxes.