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Saturday, May 17, 2008

Bats: Useful Permaculture Animals

Bats: Useful Permaculture Animals

In North American culture, bats are portrayed as scary creatures. Fortunately for me, I learned at a very young age that bats eat mosquitoes; and since learning this, I have always viewed bats as friends. Most of my permaculture designs call for bat houses, but this element of the design is usually ignored by those implementing the design or is met with strange looks when I suggest the idea. I hope this piece will explain my desire to incorporate bats into designs.

Insect Control

About 70% of the more than 1,000 species of bats in the world are insectivorous.1 They assist us in controlling biting insects, but their use in insect control is much broader than this.

Recent research from the Smithsonian Tropical Research Institute in Panama shows that bats are vital in controlling plant-eating insects. In control plots with free access for birds and bats, only 4.3% of leaf area was lost to insects. Plots with birds excluded (i.e. relying solely on bats) lost 7.2% of their leaf area. But plots with bats excluded, relying just on birds for insect control, lost 13.3% of their leaf area.2 Furthermore, plots with birds excluded had 65% more insects on the plants compared to the control plot, whereas plots with bats excluded had 153% more insects. Feeding by insects on bat-excluded plots was 209% greater than the control plot, with bird-excluded plots being only 67% greater!3 In other words, in tropical forests at least, bats are more important for insect control than birds. Surely bats play a significant role in insect control in other climates within their range as well. For this reason, I feel they should be a part of permaculture design whenever possible.

Forest Expansion and Maintenance

In the tropics of the Americas, bats can assist in reafforestation. Research by the Leibniz Institute for Zoo and Wildlife Research carried out in Costa Rica found that between 5 and 20 times more seeds are dropped around man-made bat roosting boxes than in areas without the boxes.4 The bats of the Neotropics tend to disperse many seeds of pioneering species, making them potential partners in reafforestation work.

The fruit bats of India tend to maintain forests. They eat the fruits of many canopy species such as guava, thus helping to disperse climax forest species. Unfortunately for the 12 species of India fruit bats, they are all mistakenly classified as pests by the government (though they favour overripe fruit and thus don’t compete with man).

It is also worth mentioning here that many bats are pollinators, with some plants even evolving flowers suitable to bat pollination.6

Attracting Bats

While some may indeed have bats in their belfry, it is perhaps more useful to build homes for them in locations that are beneficial to your aims. Bats seem to have an easier time locating bat roosts located on poles or on the sides of buildings, and tend to occupy them more readily. They like the interior temperature to be from 26 to 38oC.7 [See below for links to roost designs.]

Locating bat houses over gardens takes advantage not only of their insectivorous activities, but also of bat guano, a rich source of nitrogen and phosphorus.

A Few Words of Caution

The one drawback of bats is their tendency to be a reservoir species for many viruses (a species that carries a virus without showing signs of infection). They have been found to be carriers of 60 viral species, including lyssaviruses (including rabies), Henipavirus (including Hendra virus, which causes lung haemorrhaging or meningitis, Nipah virus causing neurological and respiratory damage or death), filoviruses (including Ebola and Marburg virus) and possibly the SARS coronavirus. Also, eating bats that have in turn eaten cycad seeds, which contain the neurotoxin β-methylamino L-alanine, can cause serious neurological disease.

Despite this, there is no need to go running in terror at the site of a bat. Bat roosts can be located accordingly (i.e. not next to homes); and any suspected bat bite should be seen to by a physician. Additionally, their tendency to control the populations of mosquitoes and other biting insects can make them agents of disease reduction rather than vectors of disease.

Useful Bat Links:
Bats in Australia
Some bats of India
Bats of Britain
Single chamber bat house plans
Attracting Bats
Small bat house
Successful bat houses


Smithsonian researchers show major role of bats in plant protection
Bats Limit Arthropods and Herbivory in a Tropical Forest
Fake concrete bat roosts reclaim rainforest; The Bats of India; Effects of Artificial Roosts for Frugivorous Bats on Seed Dispersal in a Neotropical Forest Pasture Mosaic
5. The Bats of India
How to Share a Bat
Attracting Bats
Bats as a continuing source of emerging infections in humans; The reservoir of Marburg virus identified in a species of fruit bat; Scientists detect presence of marburg virus in African fruit bats; Human rabies often caused by undetected, tiny bat bites; Eating bats linked to neurological disease


Mike said...

Great writeup! Thanks for the links to bat-house plans (and for prodding my memory!)

We have lots of bats living in the area (and I suspect, in the roof!) In my original veggie-garden planning I intended to plant a bat-house or two in the middle each of the (3 1x3m) compost bins. At the time though I couldn't find decent bat-house plans, and I know that getting the inner dimensions right can be critical to encouraging bats to nest in them. Then, in the course of establishing the veggie garden, digging deep beds, planting fruit trees, building the chicken run, etc., etc. integrating bats got forgotten!

I shall have to get onto it pronto.

cindy m. said...

That is a very positive write-up but I have to make a point about bats acting as reservoir species for certain emerging tropical zoonotic diseases. Bats are among the most diverse mammalian order on earth, second only to the rodents, and comprise more than 1,000 species. Any order that large is going to have evolved along with their own pathogens, and may play a role in transmission. Look at the rodent-borne diseases that have had devastating impacts on even bird-borne diseases. As for the filoviruses, dog rabies kills over 40,000 people a year worldwide.

And, Mike, if you want more info on bat houses you can email me through my simple website,

cindy m.

DJEB said...

Thank you for that note, Cindy.

Andrew said...

I'm curious about the details of transmission of the viruses. What is the primary mode of transmission for these diseases? Do I run a risk of catching some neurological or respiratory disease without even being bitten?

DJEB said...

There has been some speculation that rabies, a lyssavirus, could be transmitted by inhalation of bat saliva, but there has been no actual documentation of this having happened. On the grand scheme of life's risks however, you run a much greater chance of illness and death from the humble cheeseburger.

DJEB said...

Terrible news in the world of bats. In the northeastern United States, a fungus is killing off little brown bats and other species as they hibernate.

Thank you Scott for bringing this to my attention.

Katkinkate said...

I've heard you can site the roosting boxes over a pond and their guano would provide feed for fish.