Bats in Bangkok - the bulge under the wing is a pup [this photo is actually upsidedown as it's easier for us to look at this way]
Bangkok may be a vivid, thriving, exciting place but it is also riddled with stale and stagnant canals, drains, ponds and puddles that provide a perfect home for one of our worst enemies: the mosquito. I should know, I lived there for almost twenty years, and still shake my feet when sat at a table and try not to stand still outdoors in the early evening.
A mosquito feeding on me that did not live much longer
At it's worst the mosquito problem and my efforts to combat them were absolutely forefront in my mind. Every morning I would go outside and stand on all our shoes to kill whatever mosquitoes had hidden inside them to rest for the day. And we became experts at opening and closing the screen door as quickly as humanly possible.
But it could be worse. Much, much worse. And here is why it isn't.
Close look at a Large-footed Water Bat
There are two closely-related species of insectivorous bat, Myotis hasseltii and Myotis horsfieldi, which we can collectively call Large-footed Water Bats. They eat small, soft-bodied insects around waterways and can be found in Bangkok. They don't only eat mosquitoes but mosquitoes are definitely included in the menu being the right size and active in the right place at the right time. Incredibly, each bat can eat roughly 1,000 insects in a night!
And these bats are common in places like Bangkok. Just after sunset carefully watch the waterways and you will see them scouting just above the water surface, sometimes dipping to the water to use their feet to trawl an emerging insect or sometimes swooping upwards to catch one from the air. They are very active and easy to watch wherever there is enough artificial light to pick out their almost translucent wings.
Large-footed Water Bats are sociable animals
I used to find them roosting in a range of places, almost always somewhere overhanging water. Under canal bridges seemed to be a favourite place but I even found them in the bamboo of a restaurant roof where they gave themselves away with their gentle chittering sounds.
And I just realised that they may actually be feeding on our blood. Not directly like a vampire bat but indirectly via the mosquitoes they eat. Mosquitoes full of a blood meal stolen from us do fly more slowly and are certainly easier to catch.
But what made me think about how much they must be helping us was finding two large colonies in Bangkok. One was underneath the swimming pool at the university where I was working (Kasetsart). I had noticed bats coming and going in the evening so investigated more closely. The pool construction had left a gap large enough for stray dogs to walk through (and me to crouch through) that opened up into a cave-like void at least 5 metres wide and 30 metres long. And the walls had lots of cracks and crevices ideal for bats to roost in. I could see some bats and hear others but only when I counted them flying out at dusk did I realise that there were over a thousand living there.
The entrance to the "cave" under Kasetsart University swimming pool
That's one thousand bats each eating one thousand insects a night. This colony must be polishing off about ONE MILLION INSECTS EVERY SINGLE NIGHT! And many of them, possibly most of them, are mosquitoes. It would be fascinating to know if the rate of dengue fever, a disease transmitted by mosquitoes, is lower around the university than elsewhere.
A mother and pup (upsidedown again)
Then I found another colony in an even more surprising location. It was actually just a short walk from where I was living not far from the old airport at Don Muang. Underneath one of the concrete U-turns that arch over the six lanes of heavy traffic on Wipawadi Rangsit Road I saw some bats flying out at dusk. Again, a closer investigation and careful estimate as they left to hunt, made me realise that deep in the crevices created as part of the construction design lived at least another one thousand bats. Another colony hovering up another million insects from the area every night.
The Don Muang U-turn that has 1,000 bats in its crevices
As far as I know nobody else is aware of these colonies and my suspicion is that there must be quite a few more spread around the metropolis. The bats are clearly quite inventive about finding a place to roost, and if bat-food is around the bats will find somewhere nearby to spend their days. Although, there would be no harm in deliberately providing them with good roosting sites as a public health measure.
Bats huddling together under the U-turn
It's hard to estimate just how many of these Large-footed Water Bats live in a city like Bangkok but I'm sure it must be tens of thousands. They are always there if you look for them and we benefit from the phenomenal number of mosquitoes and other insects they are eating every night.
They will never eat them all, that's not how nature works. But rather than complain about a few mosquito bites, imagine just how much worse it could be, and thank the bats.
Thanks for reading!
