Most commonly bat droppings accumulate underneath the roost, and below the points bats use to access a building or a roosting area.
All UK bats feed on insects, so their droppings are made up of dried insect remains. Bat droppings can sometimes be mistaken for mouse droppings but unlike mouse droppings they do not contain any moisture and therefore will crumble easily (and look slightly sparkly when crumbled).
On extremely rare occasions there are health risks from allergic reactions, dust inhalation (e.g. if cleaning up very large quantities of droppings), and gastro-intestinal infection from consumption of droppings. These risks can all be avoided by following simple precautions (e.g. wearing a dust mask when clearing droppings) and maintaining basic standards of hygiene.
The main concern with bat urine does not relate to human health but the fact it contains high concentrations of uric acid which can corrode metal. Bat urine also causes etching of polished surfaces and staining of light-coloured fabric and porous stone such as marble and alabaster.
Managing droppings and urine
The National Bat Helpline has advice on managing droppings and urine. There are things that can be done to help, for example if the roost is accessible a layer of newspapers can be spread under the bats favourite roosting sites i.e. where droppings accumulate. This should be done when the bats are absent from the roost (usually between September – April) then removed and replaced annually. Droppings can be binned or added to compost.
There is detailed cleaning advice available to download from the Bats in Churches Project website (scroll down the page to 'Cleaning Advice and Guidelines'), whilst aimed at church buildings much of the information is relevant to other types of historic buildings where bat roosts are present.