Microbats are worth encouraging into your garden.

Not only are they delightful to watch on dusk – they gobble thousands of mosquitoes, moths and other garden pests each and every night.

A single microbat can eat  up to 1,200 mosquitoes and small insects in an hour – which has earned them the well deserved reputation of being nature’s mosquito busters. 

What is a microbat?

Microbats are tiny insectivorous bats.

In contrast to their larger fruit-eating cousins (e.g. flying foxes or fruit bats), microbats eat only insects.

Here in Australia we have almost 80 different species of microbats. Among the smallest is the Little Forest Bat. Weighing less than six grams and measuring less than five cm long – a Little Forest Bat is so tiny it could fit into a matchbox.

Combine their small size with their daytime sleeping habits – and it’s easy to not appreciate how widespread and abundant microbats are.

No matter where you live in Australia – there’s likely to be microbats fluttering through your night-time sky.

Microbats snuggled up for the day – photo by Linda Oliver

Why would you want microbats in your garden?

I convinced my husband that we need to encourage microbats into our garden with one sentence “One microbat can eat 1000’s of mosquitoes in a night”.

Microbats also eat many garden pests including moths, beetles, aphids, weevils, and crickets.

Given their voracious appetite for insects, microbats can help control garden and agricultural pests naturally.

Microbats have been used on organic farms as part of integrated pest management programs and on conventional farms to reduce insecticide use.

For example, microbats are used to manage codling moths in walnut orchards and Hickory shuckworms in a Pecan orchard.

Why can’t microbats find their own roost?

After feasting all night on thousands of insects, microbats need somewhere safe and dark to roost during the day.

Many microbats roost in trees. They typically roost in small colonies in cracks, fissures, hollows and under bark.

Trees with cavities suitable for microbat roosts are typically old or dead. The trouble is, old or dead trees are often removed from residential areas for safety and aesthetic reasons.

Combine targeted tree removal with large scale clearing of native vegetation – and microbats are running out of places to roost.

Thankfully, many microbats don’t mind living in artificial roost boxes.

How to build a Microbat Box

There’s numerous plans for bat roost boxes available online (see the resources list at the end of this article).

We used the helpful and comprehensive Bat Roost Box Kit produced by Latrobe Valley Field Naturalists.

Untreated rough sawn hardwood is ideal for making a bat box.

Smooth planed timber is also suitable – but the outside surfaces will need to be roughed up so that microbats can easily climb on and around the box.

We used a mix of recycled Ironbark floor boards and a piece of hardwood from our local recycled building materials yard.

Once you have you timber and your plan, it’s simply a matter of marking out the pieces onto your timber and cutting them out.

The landing surface and inside of the box needs to be rough so that the bats can climb and hold onto it.

One option is to line the inside with shadecloth or hessian, fixing it in place with staples.

Another option (which we went with) is to cut grooves into the timber.

We also cut grooves onto the outside surface of the side panels given that we used smooth, planed timber.

Above is our bat box ready to assemble:

• Top row: The landing plate and rear of the box.
• Middle row: Base of the box, internal block and two side panels.
• Bottom row: Roof/inspection lid and front of the box.

An internal block screwed under the inspection lid helps to keep the inside of the box free of draught and light.

It’s important that all screws, hinges, latches and glue be suitable for outdoor use.

Different sized entrances will attract different species of microbats.

Providing a variety of boxes with small entrance slits (12 mm) and larger entrances (15 – 20 mm) will attract a range of microbat species.

Microbats prefer entrances that are only just big enough for them to squeeze though – as larger entrances are also likely to let predators inside.

The entrance to our first bat box is 20 mm and will appeal to larger microbats.

I’d like to make a couple of boxes with narrower entrances (as narrow as 12 mm) to attract smaller microbats too.

The smaller microbat species are more likely to feed on mosquitoes – whereas larger species feed on larger insects like moths.

Improve the durability of your box by painting it with a natural waterproofing oil (we used linseed oil) or an exterior gloss acrylic in a camouflage green or brown colour.

Do not paint the landing pad.

Putting a latch on the inspection lid is optional.

We have lace monitor lizards in our neighbourhood that would happily climb up a tree and open a box for a feed – so we put on a latch.

Where to put your Microbat Box

Mount your bat box on a tree, pole or building – high enough to prevent vandalism and protect the bats from predators and floods.

At least 3-4 m above the ground is a good start. Choose a location with a clear flight path to the box.

If mounting on a tree, use coach screws rather than strapping – because over time a strap will strangle the tree, causing it to drop its limbs or die.

Microbat box building resources:

• Nest Boxes for Wildlife, A Practical Guide by Allan and Stacey Franks, Published by Bloomings Books, Melbourne 2003
• Bat Roost Box Kit including helpful carpentry drawings. Produced by the Latrobe Valley Field Naturalists and shared online by the Australasian Bat Society.
• Boxes for bats, Australasian Bat Society
• Building a nestbox for microbats, Tweed Valley Wildlife Carers
• Building a bat box, ABC Gardening Australia
• Bat Box Information Pack, Bat Conservation Trust (UK)
• The Bat House Builders handbook, Bat Conservation International

Where to buy Australian-made bat boxes

Perhaps you would love a bat box – but don’t have the time to make your own?

Bat boxes can be purchased. But a word of caution – some commercially available bat boxes are simply ornamental and are not suitable as microbat roosts. Typical faults include being too small, not being made of durable timber or hardware, and having entrances that are too large.

From what I can tell from their websites – good bat boxes can be purchased from Latrobe University and Hollow log homes.

Many Men’s Sheds also make nest boxes for Australian wildlife.

Discover which microbats occur in your area

• The Australian museum provides a list of bats for each state of Australia.
• Atlas of Living Australia. Use the “Species by location” function to map and list bat records for your region.

I was pleased to discover that 23 different microbat species have been recorded in my neighbourhood, including the tiny Little Forest Bat, the surprisingly cute (given its name) Little Mastiff-bat, and the chubby-looking Chocolate Wattled Bat.

A word of caution…

Do not touch or pick up a microbat! Microbats in Australia can host Lyssavirus – which can be transmitted to humans through bites or scratches.  

And lastly, if you discover an injured microbat, contact WIRES or your local wildlife rescue service.

Best of luck encouraging microbats to your garden!