Horned mason bee: profile, fun facts and photos
by Michael Watson (comments: 0
As soon as you set up a wild bee hotel, the horned mason bee is usually not long in coming. As early as the end of February, wild bees are buzzing and humming in our latitudes and colonize all the cavities they can find: Nesting aids, insect hotels, plant stems, beetle burrows, cracks in walls, crevices in rocks and so on. There really is no cavity in which the mason bee will not nest! It can also happen that mason bees nest in garden furniture, garden hoses or even hubcaps. The wild bee expert, Werner David, even refers to this as"nesting site anarchism"!
Name | Horned mason bee |
Scientific name | Osmia cornuta |
Size | ♀12–16 mm ♂10–13 mm |
Flight time | End of February to beginning of June |
Occurrence | Frequently |
Flower preference | Unspecialized: Apple, pear, Christmas rose, willow, violet |
Habitat | Settlement areas, gardens, parks, forest edges |
Nesting method | Nests in existing cavities, cracks in walls, crevices, nesting aids |
How do I recognize a horned mason bee? Profile and identification guide
Osmia cornuta is a (still) relatively common species of wild bee. The females grow to between 12 and 16 millimetres; the males are somewhat smaller at 10 to 13 millimetres. The mason bee is quite fluffy, which leads many laypeople to assume that they are looking at a bumblebee.
The horned mason bee is also easy to confuse with its close relative the rusty mason bee(Osmia bicornis). Nevertheless, there are some distinguishing features between the two wild bee species: the head and thorax of the horned mason bee are black, its abdomen is red. The rusty mason bee, on the other hand, has a reddish or sand-colored thorax. If you are still not sure whether you are looking at a horned or a rusty mason bee, you can check the flight times: Osmia cornuta flies from the end of February to the beginning of June; Osmia bicornis flies from March to June.

The horned mason bee also has a flat head shield on which there are two curved horns. You can tell the males from the females by their facial and head hair, as the male mason bees have a white beard and white head hair.
Is the mason bee endangered? Lifestyle, nesting site and occurrence
The horned mason bee prefers to live in urban areas, gardens, parks and forest edges. It may seem counterintuitive at first that a wild bee prefers the city to the countryside - but the wild bee has its reasons. First and foremost: industrial agriculture and the resulting lack of food in rural areas. The use of pesticides, monocultures and the over-fertilization of agricultural land means that wild bees are simply running out of food in many places. Experts refer to this as insect mortality and the biodiversity crisis.
The adaptable mason bee has therefore turned its back on the hinterland and is now found almost exclusively in cities and residential areas. On the one hand, it finds a richer food supply here; on the other hand, the mason bee also needs a mild (and early) spring, which it also finds in urban areas.
As already mentioned, the horned mason bee is very adaptable. It is also not at all fussy when it comes to choosing a nesting site and makes itself at home anywhere: garden hoses, furniture, beetle feeding galleries, hubcaps - the list is long. So it's no wonder that wild bee expert Werner David has affectionately christened the mason bee the "nesting anarchist". Apart from such more exotic nesting sites, the mason bee colonizes cracks in walls, rock crevices and nesting aids. The female mason bee lays an egg and a food package (consisting of pollen and nectar) for the future larva in each brood cell. She then closes the brood cells with moist soil and sets off. Thanks to its adaptability, the horned mason bee is not threatened with extinction and is not considered endangered.
Which plants does the horned mason bee like?
Osmia cornuta is also a relaxed guest when it comes to choosing food. It does not specialize in particular flowers and helps many fruit and vegetable gardeners with pollination: apple, pear, blue star, Christmas rose, cherry, crocus, violet, willow and many other early flowering shrubs and trees are visited by the horned mason bee.

Can mason bees sting?
Like almost all wild bee species, the horned mason bee has a stinger - but it doesn't use it. Almost all wild bees are scaredy-cats. They prefer to flee before getting into a dicey situation. And if a mason bee does get into a situation where it has to unpack its stinger, you don't need to worry. This is because their stinger is so fine that it cannot penetrate human skin. So you don't need to be afraid when you stand at the wild bee hotel and watch the busy mason bee at work.