Exoneura - Reed bees

The Exoneura bees, which are commonly called reed bees are endemic to Jervis Bay. During spring I will see many of them, especially when the native peas are flowering along my preferred walking track. I have tried to be species specific in the past but been told this particular genus needs to be revised by taxonomists to properly identify them. So I will stick to the broader term of exoneura. These are small bees, 5-8mm long with a distinct red wedge-shaped abdomen and yellow face markings. (Peter Abbott - Native Bees of the ACT and NSW South Coast)

Last year I was wandering along my normal track in late August when I noticed an exoneura bee examining the stump of a small casuarina tree which had snapped off in recent high winds. For half an hour I watched her examine every nook and cranny and then come back and reexamine. She was looking for a site to make a nest.

The following day she was well and truly carving out her nest. Her abdomen can be seen through the nest hole (approximately 3mm) and saw dust can be seen at the entrance and on her abdomen. For the next two days I saw nothing and assume she was deeper into the nest carving out her nesting chamber. On the fifth day she was seen entering the nest.

In the literature I have read that these bees quite often form groups which use the same nest. During the time of observing I only saw one bee at the nest and that was infrequent. Most times I visited I would watch for 10-15 minutes and saw no action.

Nine days after the bee was first sighted there was a mixture of pollen and saw dust at the nest entrance. The Exoneura collect pollen from a number of native species. It is normally collected in the hairs on the hind leg. As it has entered the nest some of the pollen has scraped off and was left in the entrance. It was also on a ledge below. What it means is she is now provisioning the nest. She will lay an egg on a mixture of pollen and nectar within the nest. When the larvae hatch they have the pollen and nectar to sustain them as they develop.

For the next couple of months I visited the nest on most days but never saw a bee. I also visited at different times. The only indication that the nest was still active was the sawdust at the entrance. Normally the entrance was open but every now and then it was covered in sawdust. There was no correlation in weather or time to indicate it was closed for a reason. Therefore, I assume it was closed when she was excavating, and the sawdust was moved to the entrance. Twenty-four hours later the entrance was open.

The last time it was seen with sawdust was mid-October. Every other visit during summer was just a hole in the tree with no sign of pollen or sawdust. There was no sign the nest was still active.

Then in late February the nest was seen closed with a mixture of vegetation. It has remained that way throughout Autumn and winter. A check last week showed it is probably open with vegetation missing and a distinct hole visible. As there was no action by the Exoneura for a few months I assume the nest was taken over by another insect and it closed it for the winter. At this point I have not seen any insect around the nest for some time but will keep checking.