Mortar or mason bees have got their name through their habit of being able to dig out the mortar between bricks to access the wall cavity (although they will use any ready-made gaps such as weepholes).
In severe attacks, their activity can loosen brickwork. However, they are not considered a safety threat to humans as they are a solitary bee – they do not build nests of multiple individuals, but simply access the wall cavity as a place to lay their eggs. Typically they target walls which get a lot of sun to keep their young warm.
European wasps are an invasive pest and are only found in the temperate areas of Australia, generally to the south of a line between Perth on the west coast and the Hunter Valley on the east coast. Their nests can grow very large, sometimes over 100,000 individuals. They are a dangerous, aggressive paper wasp that can attack, delivering multiple stings. Although 80% of European wasp nests are generally underground (for example in a hollow in an embankment), they will nest in roof voids and sometimes wall cavities.
Typically they will enter through natural construction gaps under the eaves, but will access the roof void through any hole in the walls – including gaps around windows and door, as well as weep holes.
Although they generally don’t do much damage, they do represent a significant safety threat.
Native paper wasps
There are a variety of native paper wasp species found across Australia. Their nests are much smaller than the European paper wasps and although they also deliver a painful sting, they are generally less aggressive.
Native paper wasp typically don’t nest inside walls or roof voids, preferring to build their nests in sheltered areas on the outside of buildings, such as under the eaves.
Mud dauber wasps
Mud dauber or potter wasps which are found across Australia create a specific but significant problem with their nesting habits. Their nests are temporary and are built solely as a nursery for their young. They build mud capsules into which their place a paralysed spider or caterpillar as food for their larvae. They require a surface on which to build their nests and locations which provide additional structural support for their nests, such as the edge between walls and ceiling, or in the corners of rooms, are ideal.
Mud dauber and potter wasps will typically building their nests under eaves, but occasionally in outbuildings or roof voids. However, weep holes are also a preferred location as they provide good support for the mud cells.
Whilst they generally cause little direct damage, by blocking up the weep holes they prevent the weep hole from doing its job – allowing good ventilation and moisture to escape. If they block up several weep holes in the same section of wall this can start to cause problems with moisture in the wall cavities and potential decay of wood elements.
Installation of stainless steel Weepa Protector Weep Hole Screens will discourage mud dauber wasps from building their nests in weep holes.