What To Do About Bats In The Roof

Please remember that although bats sometimes get in our way, we are more often in their way. Bats have lived on the Cayman Islands for 25,000 years. Humans have taken over many of their original habitats and feeding grounds. The bats are just trying to use what is available to them now, in a very changed environment.

Bats are ecologically important native animals, but they do not belong in your roof! Bats do not damage buildings, invade food or carry diseases, but droppings cause odour problems. It is important to seal bats out – not in! Trapped bats can find their way into to living areas, so read these instructions carefully and ask for assistance and advice from the National Trust. Do not plug holes unless bats are out.

Only insect-eating bats live in buildings. Fruit bats roost in smaller groups in caves and thick bush. If you farm, garden or don't like mosquitoes, remember that each bat in your house eats over 2,000 insects, including garden pests every night! 

Bats that roost in houses are usually our common Velvety Free-tailed Bats, but rare bats sometimes find their way into roof spaces too. Some of these are found only on a few Caribbean islands, and one is only on Grand Cayman! It is important to protect rare species, but our common bats also need protection. Large bat colonies eat millions of insects every night and are important links in the ecosystems.

The mere presence of bats is not a problem. Bats are not related to mice and rats. They will not invade the living quarters, chew wood or wires or damage the building in any way. Bats are not vermin! They pose no health problem for humans or pets. If bats are over a patio or garage or in the eaves over the garden, don't worry! Some people simply spread a plastic sheet under the bats and collect the guano (bat droppings) to use as a fertilizer. (Use it carefully; it is very strong!)

If bats are living in your roof and you want them to leave, there is a well-researched and effective way to remove them. Bat guano build-up inside roof spaces is the main reason to remove bats from your building.

Do not plug bats' main exit holes without first getting the bats out. If you have a bat problem, call the National Trust at 949-0121 and ask for our free information. We can recommend a reputable company to help you, or give advice about “Do It Yourself" bat exclusion.

The National Trust’s volunteer Wildlife Rescue team can assist you with your bat exclusion, but you can begin the process yourself with these simple instructions.

Watch all sides of the building at sunset. Bats leave their roost every night to feed, except in very bad weather. Bats generally emerge from only one or two holes (usually on the western side of the building). Leave these holes open.First, seal only the holes that bats are not using. Use a material that blocks light and air so the only light will come from exclusion device and bats will find it easily to leave through it. Use screen folded into black plastic (pieces of heavy-duty trash bags work for a temporary fix), or use wood, cement, caulk backer rod, caulk, or whatever is right for your building. Do not use spray foam because bats become stuck in it and die, and it is not long-lasting as a roof repair. It dries and crumbles in the sun and falls away, allowing the bats to get back inside the roof. Bats don’t chew new holes, but they can squeeze through very tiny cracks. To see this illustrated with photos visit www.caymanwildlife.org and open the PPT under the “Bats” tab.

If bats are entering through a missing vent in a soffit, the National Trust can lend you an exclusion device for a small deposit. Bats can leave through it, but cannot re-enter the roof. Allow several days for all the bats to leave. Be sure they are not still using any other openings. If the weather is bad, it may take up to a week for them all to come out. Watching carefully after the exclusion will show you if bats have found a new way inside.

Be sure to look for other holes. Sometimes several different colonies of bats are in separate compartments that are not connected. You will need a separate exclusion device for each compartment.

Never evict bats during June, July, August, September, October or early November when baby bats would be separated from their mothers and left to die. This is unwise, as bats bear only one baby a year and an entire generation would be lost. Dead baby bats in your attic will also cause an odour problem in your house. Guano can be carefully vacuumed without harming the bats to reduce odour during summer months.

Every exclusion is a little bit different, so call the National Trust if you encounter any unusual situations or difficulties. 

To make your own bat excluder, use a hole-saw or a jigsaw to cut a 3” hole in the center of a piece of plywood. Insert a 5 inch long section of 3” PVC into the hole and fasten it from the inside of the top of the pipe with screws. Put this over the bats’ exit hole, seal all the edges and leave it there for a few days or longer. Bats will leave through the pipe, but cannot get in again. 

Be sure the inside end of the pipe is even with the interior floor, so bats can drop through easily. The best time to install the device is at dusk, after most bats have left the building. This prevents panic if hundreds of bats are trying to fly out of the new exit.

Continue to watch at dusk for a few days to be sure they are not using other openings to get back inside. Allow several days for all the bats to leave. If the weather is bad, this may take longer. All the holes must be plugged permanently AFTER the bats are out.

Put the excluder device over the hole where the bats are coming out facingstraight down as shown in the photo. If you must install it horizontally, put an elbow in the pipe so the end points straight down.

An excluder can also be made from softer materials like this one, which uses a mouse pad and length of hose. Be sure the hose is smooth and slick on the inside and outside, so bats can’t cling to it and climb back in. The mouse pad can be cut with scissors to fit into small, irregular paces and is lightweight enough to use with plastic soffit panels. The open end of the pipe must point straight down so the bats can’t fly back into it. Monitor for several nights to be sure this has worked and that no bats are trapped inside.  Always monitor all bat exclusions.  Visit www.caymanwildlife.org to download free a PowerPoint with photos and detailed instructions.

A less successful method that sometimes works but must be monitored carefully can be tried in areas where a pipe cannot be mounted. Tape or staple a piece of clear plastic or netting loosely over the main exit. This should be cone-shaped and works like a reverse fish trap – letting bats out, but not back inside. It should hang down two feet below the hole. Seal the top and sides, but leave the bottom open. The bats will come out under it, crawl to the bottom opening and fly away. When they return they shouldn’t be able to re-enter. This works best if the wall is a smooth surface. If the wall has a rough surface, bats may be able to land on it and crawl back up under the screen. Watch for at least three nights to be sure this is working properly. Recently, bats in the Cayman Islands have learned to land on screen excluders and go under them, so this method only works if it is carefully monitored. Watch and listen for several nights while you are removing bats. If you hear squeaking and bats are stuck and can’t get out, loosen the netting. It may take several adjustments to get it right. Every exclusion is a little bit different. If bats are still getting back in, modify your design.

All the holes must be plugged permanently AFTER the bats are out. Use wood, cement, caulk, caulk backer rod or whatever is appropriate for your building. If you do not give all the bats enough time to leave before plugging holes, dead bats will be an odour problem in your house. Bats don't chew new holes to get back in, but will sometimes chew their way out. Then, after the new hole is there, they will use it to come back in. Bats can squeeze through very tiny cracks.  If the holes are not properly sealed, the bats will return.

When the bats are all out, the roof space should be vacuumed, but this is not good for your home vacuum cleaner! – Contact us for recommendations if you would like to hire someone to do this job for you.

In houses with Spanish tile roofs, bats are usually not actually in the attic space but under the tiles. In this case, bats can be allowed to stay. No harm will come to the house or the people living in it from these bats. The droppings are simply blown away in the wind. If the bats are under tiles that are over patios or pathways, they can be carefully removed by plugging the holes after the bats have gone out at sunset. This is difficult because sometimes a few bats will stay behind, especially if they sense something is unusual. The hole will have to be re-opened for a few minutes for three to five nights to make sure they are all out. Before sealing the opening, count the bats as they leave at dusk, about 10 minutes after sundown, while the sky is still light. Do this for a few nights and note the exact time and number of bats. On the night that you plan to seal the exit hole, have your ladder and supplies ready and work quickly when the last bat has gone out. Then, the following night at the same time, remove the plug for one or two minutes to be sure they have all left. Do this again for a few nights to be sure they have all gotten out before you finally seal the exit hole with something permanent.

There is never a reason to poison bats. Attempts to do this are hazardous to humans and unnecessary. Since bats will not take bait, poisons used on them must be breathed or absorbed through the skin. These types of poisons are not healthy for children, pets, old people, or anyone else!  Some bat poisons are deadly to people. Burning sulfur or commercial bat repellant products (usually just mothballs!) doesn’t work. More bats will move in if all the openings are not closed. Killing bats only adds to the difficulties.

Bat Houses Are Fun, Educational, And Good for the Environment!

An important part of moving bats out of your building is to give them another place to go. To provide housing for our valuable bats, and to keep them from moving into your neighbour's roof space, buy or build a bat house for your excluded bats. Install your bat house a few weeks before your plan to do your bat exclusion. Be a good neighbour and provide the bats with a safe, permanent home. Free plans for building your own bat houses are available from the National Trust, or completed bat houses may be purchased. Ask at the Trust for a free inspection of your property and advice about where and how to mount your bat house.

Cayman Islands' bats need someplace to live. They are not welcome in people's attics and roof spaces, and most of the old forests have been cut down to make way for development. The Cayman Islands have the most successful bat house program in the tropics. There are already nearly fifty occupied bat houses. Our goal is for all roof-bat species to be in bat houses and NONE in roofs!

There are always colonies of bats looking for new homes. People can enjoy having a bat house in the garden. Watching and counting the bats as they fly out each night is interesting and educational. Droppings can be collected from underneath the bat house and used in the garden. Only insect-eating bats will live in bat houses. Fruit bats don’t use them.

Remember, never evict bats during the summer months of JUNE, JULY, AUGUST, SEPTEMBER, OCTOBER or the first two weeks of NOVEMBER when baby bats would be separated from their mothers and left to die. This is cruel and unwise. Bats have only one baby each per year and an entire generation could be lost. Dead baby bats would cause an odour problem in the house. On rare occasions, it is possible to look inside the roof space during the summer and ascertain if bat pups are present. In some cases they are not, and in other extreme cases it is possible to bring the bat pups into captivity to be raised but these are last resorts and are often not possible. Contact 917-BIRD or visit Caymanwildliferescue.org for more information.

Visit www.caymanwildlife.org to download a free PowerPoint with detailed photos and instructions call 917-BIRD or contact info@nationaltrust.org.ky,caymanwildliferescue@gmail.com or info@caymanwildlife.org