Giant resin bee Megachile sculpturalis in France

Up to 25mm in length this huge leafcutter bee is a relatively new arrival in France that is rapidly and literally making itself at home and is nicknamed the Squatter bee for reasons that will become apparent. 

First observations of this bee in France were made in 2008 in Allauch, north of Marseille. Since this date they have spread a long way and in the space of a few years have conquered a territory that includes all the southern half of the country!  The main concentrations not surprisingly follow the Rhone valley as far as Macon in the north to the Mediterranean in the south spreading West as far as Spain and East into Italy, Switzerland and Germany becoming relatively commonplace in gardens south of Lyon.

Map source - VigieNature

It is thought to have first arrived in a shipment of timber into the port of Marseille from the USA where the species had been introduced at an earlier date, (first observed in 1994 in North Carolina). Originally the species is found throughout the eastern Palearctic and Oriental regions including Japan, China, and other parts of eastern Asia.

Although the species is known to fly great distances the main advantages that are aiding their rapid expansion are due to their nesting behaviour and diet. Although some native flowers are used for nectar and pollen collection there is a marked preference for plant species introduced from Asia for ornamental purposes. In some cities like Nîmes and Montpellier, the pollen analyzed shows a predominance of Sophora japonica ... at nearly 96%! This ornamental tree with white-cream flowers is very popular with city dwellers: it adapts well to polluted environments and grows quickly and despite the name is native to China.

For nesting it mainly uses the large holes that have been made by the Carpenter bees Xylocopa violacea &  Xylocopa valga but unfortunately not only when they are disused occasionally aggressively ejecting any occupant with its powerful mandibles.  A hole of around 10 mm is preferred which females prepare using resin and sap collected from trees although mud and other materials may be made use of. As with other leafcutter species, an egg is placed in a cell, provisioned with a pollen ball and sealed, a process that continues with up to 10 cells, the last which that is open to the air being sealed with a hard coat of resin. After hatching, the larvae feed on the pollen and overwinter in their cells pupating in late spring before emerging in the summer.  

They have also been found in a large number of bee hotels where larger tubes or holes are ideal for them.

It’s highly likely that this species will have a serious impact on the ecosystem in France both directly on our large carpenter bees and on the available sources of forage for other pollinators.

Chris