Introducing the Red Mason bee, article for BTO Garden BirdWatch magazine

June 1, 2014

in Gardening For Wildlife, Other organisations, Red mason solitary bees, Solitary Bee Observation Box

 The BTO Garden BirdWatch is interested other garden wildlife too, mason bees!


Red Mason bees


Garden BirdWatch Ambassador George Pilkington introduces the Red Mason Bee, a species common in gardens but easily overlooked. As George reveals, these solitary bees provide a great opportunity for the interested ‘amateur’ to reveal new and exciting information.

Bumblebees and honeybees live in a social nest and work for the benefit of their siblings. Solitary bees may nest in aggregations but work alone. Within the UK there are more than 250 different species of wild native bee and, of these, the Red Mason Bee is probably the best known and best researched. Red Masons are spring bees and activity begins from mid- March onwards, depending upon where you live. They will often use man-made solitary bee boxes.

To prosper Red Mason Bees need three different things within a relative small area: a) forage, b) nest site, c) mud. Without any one of these three requirements the bees will not nest in that area.


Both sexes overwinter as adults using silk cocoons inside cells, placed inside cavities, females at the innermost end, males nearer the opening. In spring, as temperatures rise, the smaller ‘moustached’ male bees are the first to wake from hibernation. Each has to chew its way out of its cocoon and mud partition. Bees on the innermost cells, being older, generally wake before the one in front. After freeing itself, it may be faced with a cell containing a sleeping bee. The preceding bee nips the backside of the sleeping bee, which then starts its own emergence. They feed up and wait for the females. As they mate just once, there is a mad scramble as soon as the females emerge. George has often observed males mating with females before they have even left the nest.


The newly emerged female needs to find food, (nectar and pollen) to replenish her fat reserves and mature her ovaries. Ensure you have plenty of solitary bee-friendly flowers in your garden. Dandelion is a top early favourite, together with Perennial Wallflower (esp. Erysimum Bowles Mauve), Meadow Cranesbill, Borage, Lavender and fruit tree blossoms.


Once suitably fed, the female will search for a nest site. In the wild, Red Mason Bees are catholic in their choice of nest sites. Cavities in sunny sandy banks, fallen dead logs, hollow plant stems and beetle borings in dead wood are all used. They also use holes in the mortar between bricks, but they do not excavate these themselves. Their name actually comes from the fact that they use mud to build walls within their chosen nest site. Mud or moist soil is used to seal both ends of the chosen nest cavities and to construct the individual cells inside.

The female’s life evolves around repetitive stereotyped behaviours: seal rear of cavity; forage for pollen; forage for nectar; lay a single egg; seal cavity; forage for pollen; etc. Just prior to completing her cavity, the female will start to look for another suitable cavity. During inclement weather she sits inside her cavity entrance jaws ready to repel other bees or possible predators.


Once the female has laid her eggs she dies, living between 10–12 hard working weeks, if she is lucky! The males die once they have mated. There is only a single generation a year. The larvae that emerge from these eggs will feed from the stored pollen and then, about late August–September, they spin a silken cocoon and enter the pupal stage. By early October they will have emerged as fully-formed adult bees and it is in this form that they will sit out the winter until spring, when the cycle begins again.


Unguarded nest sites make rich pickings and do not go unnoticed in nature. Besides a few minor predators, there are three major pests. Pollen mites (Chaetodactylus osmiae), which may be present in the cells, compete with the larvae for the stored pollen and many larvae loose out and die. When numerous, the mites may even eat the mason bee eggs. Then there is the fly Cacoxenus indagator, which lays its eggs in open unguarded cells, whilst the females are foraging. The larvae eat the pollen and starve the bees. Tiny, silent assassin Monodontomerus wasps deposit several eggs inside the cocoon which hatch and eat the bee. A final threat is Chalkbrood, a fungal disease of bees, which causes the death of infected larvae.


Red Mason Bees can be attracted to use nesting tubes and boxes. Some box designs may have a negative effect on the bees and their larvae by enhancing pest populations or by failing to deal with disease issues. Growing awareness of these issues has seen the development of new and better designs of box, something with which George has been involved. Find out more:

Red mason bee


14 Bird Table Spring 2014

Red Mason Bee, Andy Callow © ( Mating Red Mason Bees; Bees waiting to emerge from nesting tubes; bee larvae, all by George Pilkington

See a video of the red mason bee’s life cycle  with a detailed account and photos here…

For more information about BTO Garden BirdWatch

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