Spotlight | Macroplis europea, the yellow loosestrife bee

30th November 2023
by Peter Morton

Throughout July and August our wetland flora really comes to life and the reed beds become an extravaganza of colours. The summer flowering provides an array of whites, pinks, oranges, reds, purples, blues all against a backdrop of lush, mottled greens. In two particular compartments of fen at Withymead a bold show of yellow can be seen.

This blanket of yellow is of course provided by none other than the yellow loosestrife which makes its home only in wetland habitats in the south of England. In the UK we have an estimated 275 different varieties of bee, including bumblebees, honeybees, and solitary bees. Often, these solitary bees have developed a symbiotic relationship with one or two of our native flora and time their life cycles to synchronize with a specific flowering period. One fine example of this symbiosis is of course the yellow loosestrife bee (Macropis europea).

These wetland specialists are the only member of the Macropis genus which can be found in the UK. What sets these bees apart from other solitary bees is the fascinating tactic they have developed in order to thrive in their niche habitat.

The genus Macropis is broadly known as oil collecting bees, and for good reason. Unlike most plants yellow loosestrife does not produce nectar, but instead produces pollen and fatty floral oils. With specially developed hairs on the fore and mid tarsi these oils are collected and utilised by the bee to great success.

In wetland environments flooding is more than just a possibility and a likely annual occurrence. This poses a great number of risks to a burrowing bee and their developing young. While most would search for higher ground and dryer soil Macropis europea has developed a tactic to mitigate the wrath of winter. By collecting the oils of yellow loosestrife and mixing it with the pollen these bees are provided with a much-needed building material and the flower receives the pollination it had hoped for. Once a burrow has been dug the females line the tunnels with this natural waterproofing before beginning to load the chamber with supplies collected from other local flora. Eggs are laid and the cells are capped, leaving the larvae to rest easy through the hardships of winter and ready to emerge the next summer and begin the cycle again.

The yellow loosestrife bee was classified as ‘Rare’ in 1987 and ‘Nationally notable’ in 1991. The Bees, Wasps and Ants Recording Society suggest the status needs review. Given the developments in agriculture and the ever-changing landscape since 1991 I would hazard to guess the distributions are becoming increasingly fragmented. It is a delight to be able to say we seem to have a happy and healthy population of these wetland specialists, and even more of a joy to be able to care for the habitat they call home.

25th August 2023
by Pete Morton