106 



THE AGRICULTURAL NEWS. 



Mak(;h 28, 1914. 



INSECT NOTES. 



THE ERADICATION OF MOSQUITOES BY 

 THE CULTIVATION OF BATS. 



A very brief reference to this article was made in 

 a recent number of the Agricultu7-al JVeivs (see page 31 of 

 the current volume) under the heading Economic Value of 

 the Bat. The subject of mosquito control seems to be of 

 sufficient importance for a more extended account, which is 

 presented herewith. The conditions which exist in certain 

 cf the AVest Indian islands are such that it is likely that 

 artificial bat roosts would not be of any great value, but in 

 others they might be found useful in increasing the numbers 

 of an enemy of mosquitoes that does not appear to have been 

 taken into account to any great extent in these colonies. 

 The value of the guano which must be thus obtained would 

 seem to be sufficient to cover the expense involved; if not 

 indeed to yield a substantial profit. 



An interesting communication under the title which 

 apipears above \\as leviewed in the Montldt/ Bulletin of 

 Aflrindhiral Intelligence arid Plant Diseases, August 1913. 

 The author of the article is Dr. Chas. A. R. Campbell, 

 San Antonio, Texas, USA. The following notes are 

 abstracted from the review. 



The writer refers to the general nature of the relation- 

 ship of the mosquito to the development of the malarial 

 parasite and its dissemination in man, and to the estimate of 

 Pr. L O. Howard, Chief Entomologist of the United States 

 Department of Agriculture, which is considered a conserva- 

 tive one, that the United States pays an annual tribute to 

 malaria amounting to one hundred million dollars. 



The bat is stated to be the greatest natural enemy of 

 mosquitoes. In order to ascertain what proportion of the 

 food of bats, mosquitoes formed, the writer utilized a small 

 hunter's cabin where the bats congregated. He spread 

 a white sheet on the floor, after stuffing with rags all roosting 

 places except directly above the sheet. The bats were 

 counted as they came in the morning, checked by counting 

 after they were at roost, and again as they went out in the 

 evening. This was repeated three times on consecutive days, 

 and the guano carefully collected and examined with the 

 result that it was found that each bat dropped twenty- 

 six pieces of guano each day, from morning to evening at 

 a time of year (November) when mosquitoes were compara- 

 tively scarce: the number of droppings per day of twenty- 

 four hours was estimated at fifty. Careful examination of 

 the droppings resulted in the opinion being formed that in 

 each of these they were the remains of ten mosquitoes, thus 

 indicating that the food of one bat for the day included 

 some 500 mosquitoes and these comprised, on an average, 

 90 per cent, of the food of the bat. 



The author after extended observation estimated that 

 the natural bat roosts contain a population of at least 

 500,000 bats per roost. 



The commercial value of the guano produced in such 

 a roost is estimated at .$600 per year. 



Dr. Campbell, believing that from a hygienic point 

 of view alone it would be profitable to afford protection to 

 bats in any mosquito infested district, experimented 

 with difterent styles of structures to provide artificial 

 roosting places for these animals, and realizing at the 

 same time that such a practice would be more likely 

 to be adopted if it were financially profitable, he made the 

 estimate given above, and in addition found that an artificial 

 roost with accommodation for -500,000 bats would cost, at 

 the very outside, -§1,200. 



As a result of these experiments 'Dr. Campbell's Hygi- 

 ostatic Guano- Producing Bat Roost' was built. The struc- 

 ture described in the article under consideration was 

 intended as a model, but it has proved to be much more 

 than that. 



The structure itself is 20 feet high, 12 feet square at 

 the bottom and 6 feet square at the top, erected on four posts 

 which raise it 10 feetfrom the ground. On the posts are con- 

 trivances for preventing enemies of the bats from gaining 

 access to the roost. The bottom of the structure is built as 

 a large hopper under which a waggon can be placed, to 

 facilitate the collection of the guano. 



The principal enemies of the bats are the racoon 

 (Procpon liiior), opossums, skunks, wild cats, civet cats 

 ( Viverra civetta), and chicken snakes {Coluber quadrivittatus). 



The inner construction of the roost (which is of course 

 the most vital) is based on lines, after long and careful 

 study, entirely in harmony with the most singular habits of 

 the bat.s. When finished the inside was sprayed with 

 a chemical solution possessing an odour identical with that 

 of the bats and 2.5Dt). fresli guano was placed in the hopper 

 at the bottom. 



The roost was completed in April, 1911. It was situated 

 on the shore of a large body of fresh water, estimated at 

 900 acres in area, which receives an influx of about 

 10,000,000 gallons per day from the sewerage system of 

 the city of San Antonio. 



The lake never overflows, the water being used for 

 irrigation. The huge amount of organic matter in the 

 water, the large pools formed by irrigation on the land, the 

 water left in the laterals, the receding water left in the lake 

 when used largely, and the large pools formed by seepage 

 outside the earthern dams are the conditions which tend to 

 make this an ideal breeding place for mosquitoes and one 

 where theconditions of mosquito control are extremely difficult. 



The bat roost was completed, as already stated, in April 



1911. lu August of the same year it was found to be 

 tenanted by a colony cf bats estimated to number several 

 hundred from the fact that it took them, flying in a con- 

 stant stream, fully twenty minutes to come out. Durincr 



1912, the colony had so increased in numbers that several 

 hours were required for the bats to emerge from the roost in 

 the evening 



In 1913, a careful and extended investigation into the 

 mosquito conditions in the vicinity of the lake revealed the 

 fact that these insects were much less abundant than formerly. 



The following is the conclusion and summary of the 

 paper: — 



'1. That the mosquito is unquestionably one of man's 

 most formidable enemies, not only jj^r se but also by the 

 subtle role he plays in transmitting disease-produc ng bacteria. 



2. That the mosquito may be considered as a good food 

 for the bat. 



3. That we can build a home for the bat where it will 

 be protected from his enemies, and propagate in countless 

 nuiubers, at the same time protecting us, by improving our 

 hygienic conditions. 



4. That the commercial feature in the propagation of 

 bats will ensure its adoption, the hygienic benefits that follow 

 will protect the community in which they are erected, 

 especially the poorer classes who know nothing of the 

 dangers of mosquitoes or the use of screens, and amongst 

 whom we find the most sickness. 



.5. That when we propagate this most useful creature, he 

 not only destroys the disease-producing mosquito that serves 

 it as food, but it actually converts that most malevolent of 

 insects into a high grade fertilizer.' 



