DO BATS EAT MOSQUITOES?

A silly question really, in that some obviously don’t, their size requiring bigger prey to sustain them, and some probably do, given that they are totally insectiverous. But to what degree and is this an argument for encouraging bats? To answer the first question I have extracted from a book Bats, Mosquitoes and Dollars by Dr Chas Campbell, published in 1925. Dr Campbell was a renowned bacteriologist who discovered the agent that spread smallpox. He was nominated for the Nobel Prize for Medicine in 1919 for his efforts towards the eradication of malaria by the cultivation of bats, the natural enemy of mosquitoes.

In the book, Campbell describes what happened when he was called to a friend’s room on the third floor of a hotel in the CBD of an American town. The hotel was not gauzed. The two of them were sitting on the floor at 4.30am gazing out at the approaching dawn through an open window.

The author was (spellbound), not at the sight of one engorged mosquito being waylaid by the bats, but at seeing every one that left the room captured with the most dextrous and unerring  certainty. Not a single mosquito escaped our eager eyes, neither did it escape the keen ears of the noiselessly-flying, acrobatic sentinels on the outside of the room."

Campbell’s first successful bat roost, built in 1911.

"A small room, 10 feet long, 5 feet wide and 5¹/₂ feet high, was thoroughly cleaned, canvassed and white-washed. The room had one small window to the east and a door to the west, both of which were thoroughly screened with fine wire mesh. Tens of thousands of mosquito eggs were procured and placed in a tub of cistern water, to which there was previously added some organic matter to furnish food for the larvae. In the course of time thousands of mosquitoes hatched out and these were fed by placing two turkeys and two old fat hens in the room until all the mosquitoes were hatched."

"At night, after the mosquitoes had developed into adult insects, their buzzing noise could be plainly heard several feet from the room. On one occasion the writer entered the room with a darkened electric flash light and liberated two bats. Instantly the buzzing noise ceased and, on turning on the light, it was observed that the mosquitoes were clinging to the walls and perfectly motionless. On taking the bats out of the room, in less than three minutes the buzzing noise resumed. This experiment was repeated several times with the same results."

"This is to certify that we, Cesario and Ramon Miranda, have lived on Mitchell’s Lake since 1907. During the years 1907-1910, mosquitoes appeared in clouds. In 1909 we were both very ill with malaria. In those years it was a sacrifice for us to irrigate at night and no one would help us for any amount of money. During the day it was almost impossible for us to rest on account of the mosquitoes. Since the bat roost was erected, we have noticed a (steady) change. During 1912-13, we were able to irrigate at night and since 1911 we have had no signs of malaria."

By 1917, the bat roost was producing 1.3 tonnes of bat guano annually, which was harvested and sold as fertiliser.

THROUGH THE EYE OF A NEEDLE

Destroying hives of feral bees that have invaded nestboxes is messy and unpleasant. The only positive is to discover what was using the box before the bees arrived – since honey is a preservative, the remains are often in reasonable condition.

One such box contained a ringtail possum. That is not particularly surprising, but this was a glider box with a 40mm diameter entrance. It could have been a juvenile but most young don’t leave their mother until nearly full grown. Since small entrances are used to exclude competitors, finding the minimum and maximum entrance sizes for an animal is important.

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A DOLLARBIRD WITH FLEXIBILITY

Dollarbirds readily take to nestboxes but our experience with dollarbird breeding is not large. They seem to prefer a site from which they can easily launch their aerial acrobatics. This can mean a high box but they will breed lower where there is no clutter around.

So we were surprised last season when one used a very low box, under dense foliage and within metres of a busy bikeway. They are either becoming desperate or they are more versatile than we thought.

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