Chimney Bee of the Channel Islands

Description:

To my great delight and amazement, I came across an aggregation (about 1 meter square) of Digger Bees building their underground tubes along a hiking trail on Santa Cruz Island of the California Channel Islands off the coast of Santa Barbara. These bees are also called Chimney Bees because of the characteristic Turrets they build above their entrance holes. These bees, of the family Apidae (Tribe Emphorini) choose sunny areas with dirt, and while each bee is solitary and working on her own nest tube, they often aggregate in large numbers. Sometimes a bee will enter the wrong hole, find another bee in there and the two will emerge to fight. Within the holes, which can be several cm deep, the bee places a large amount of pollen and nectar and lays a single egg on the mixture. This bee was using pollen and nectar from the Island Morning Glory (Calystegia macrostegia). They work so hard creating and maintaining their dirt tubes and turrets that their wings are often tattered, as in these pictures. The third picture shows a bee working head down in her tunnel. The females often rest in the entrance to their nests looking out, before flying off for more pollen, as in the second picture. The first picture shows one of these bees in my hand with a piece of turret tubing. The turrets are extremely fragile and break almost immediately when handled. Note the long stinger-ovipositor on the bee and heavy brushes on the hind tibiae for collecting pollen. They were not at all aggressive. The last picture shows one of these bees collecting pollen in of the flowers of the Island Morning Glory. The bees are about the size of a Honey Bee. They approach the nesting area quietly, but when close to the ground and near their tunnel, they begin to buzz loudly, possibly as a warning mechanism towards other nearby bees. The ground around the nesting site was surprisingly hard and compact. The loose dirt visible in the pictures is dirt excavated by the bees themselves. Many thanks to Dr. Robbin Thorp of UC Davis for identifying this bee for me.

Habitat:

Sunny, exposed area of relatively compact dirt along the North Bluff Trail, Santa Cruz Island, Channel Islands, California.

Notes:

The turrets, like the one in my hand, are made from cementing particles of soil together with saliva. Not all of the bees made turrets. Studies have shown that turrets may have an important function in protecting the tunnel from filling with dirt and that less turrets are constructed on level ground than when located on a slope. Turrets on level ground also tend to be vertical, whereas Turrets constructed on a slope always pointed downwards, thus protecting the hole from filling with dirt falling from above or blown down by the wind. This site was on a slight slope and most of the holes which had a turret were pointed down hill. See the following article for very interesting reading see: "The Function of Burrow Turrets in a Gregariously Nesting Bee F. North and H. Lillywhite The Southwestern Naturalist Vol. 25, No. 3 (Nov. 14, 1980), pp. 373-378" There were also several dark Tenebrionid beetles (about 1 cm long) going in and out of the nest holes. There must be some relationship between the two. Probably not beneficial to the bee. Maybe the beetles feed on the pollen and nectar before the caches are sealed. These are endemic bees, native to California and are extremely important for the pollination of many flowers, both commercial and wild.