Wednesday, 18 March 2015

Horned Osmia ( Osmia cornuta )

Osmia cornuta is one of the first solitary bees to emerge in spring and as such is an important pollinator of fruit trees such as apricots, plums and almonds. Present in most of Europe, (not the north), it is a species that has disappeared from most areas of intensive agriculture, but it survives well in some urban areas, wastelands, public parks and gardens in particular areas. 

Given this living where we do in the intensive cereal lands I was extremely pleased to see a group of these about midday buzzing around the table on the patio in the sunshine. At first I thought they were Osmia bicolor with their bright orange abdomens and black head and thorax, not easy to see when they don’t settle. Anyway, a little later Lynne called me to say that a couple were kindly putting on a performance for me on the table and providing a photo opportunity. 

Please Click on images to enlarge. 

They are closely related to both Osmia bicolor the Two Coloured Mason Bee and Osmia rufa, the Red Mason Bee and they behave in much the same manner. The female builds a nest in an elongated hole, often in an old branch or some other piece of timber. The majority of the holes are between 5 to 8 mm in diameter and the nest is formed with a series of cells separated by clay partitions. Each cell contains a food reserve formed by a ball of pollen and nectar, on which an egg is laid. If the gallery is too long, a dirt cap is raised by the female to reduce its size. As a generalist pollen collector they will use what ever is available according to season, this is taken to the nest and mixed with regurgitated nectar to make the so called bee bread which is made into a pellet stuffed into the cavity.  When the cell is half full following 10 to 30 trips, the female lays an egg and builds a front wall with some clay and then repeats this until the tunnel is full with up to 15 eggs and then seals the outside with a clay plug. She repeats this for about two months building one nest after the other.

When the eggs hatch the one that were laid first which are to be females develop more slowly. When fully grown the larva spins a light brown thread cocoon and transforms into a pupa.

The bee is fully formed in late summer but remains where it is until the following spring.

The mortality rate is very high; perhaps 60% or more never get to fly and in part this is caused by Cocoxenus indagator, is which a ‘fruit fly’ and a cleptoparasite of Osmia species that lays its own eggs in the bees nest when the bee is away foraging. Having said that it’s built in to the numbers of eggs produced so nothing to be concerned about as long as the habitat requirements are met. 

Places used for nests include - Hollow stems; Galleries in walls, soft stones or soil; Gaps in window frames and drainage holes; Old galleries dug by other species of Hymenoptera; Natural or artificial galleries in timber with holes of a diameter of 8 to 10 mm; Sometimes even snail shells as with Osmia Bicolor. Galleries are thoroughly cleaned before any eggs are laid and can be used almost indefinitely. All of these locations are available at our place and with no chemicals or poisons they should go on to thrive.

Definitely one to look out for in France.