FORMICA. 253 



from the mouth, Andre sixty centimetres 44 , Escherich 1J-1 J m., 

 and Lubbock says a hand held as high as eighteen inches above the 

 nest will be covered with acid 45 . I have noticed it shot by these 

 ants to a distance of from six to twelve inches. 



Latreille mentions that the people in Sweden employed this 

 acid to give a taste of lemon to cream 4 , and Schenck says it was 

 used in Germany in baths as a cure for gout and rheumatism 25 . 



The fumes of this acid are so pungent as to induce coughing and 

 take one's breath away if the head be held over a disturbed nest 

 of this species. 



It is also very corrosive, and Latreille pointed out that it produces 

 pustules on the skin such as are produced by stinging nettles 4 . 

 When working at nests of these ants for several days the skin has 

 peeled off my hands, and when I have worn gloves as a protection 

 they have been burnt by the discharges of formic acid 64 . 



To determine the quantity of anhydrous acid contained in the 

 liquid ejected by F. rufa, Poulton 63 invented an apparatus, which 

 consisted of a glass tube containing filter-paper fastened to a glass 

 rod fixed in the tightly-fitting india-rubber cork. I obtained a 

 number of these tubes and collected discharges from the ants ; the 

 percentage of anhydrous acid was found to fluctuate greatly in the 

 various samples, strong samples containing from 60 to 70 per cent. 



Mr. A. Vincent Briscoe of the Imperial College of Science, London, 

 has kindly worked out for me the weight in grams of Formic Acid 

 present per ant in a number of workers of Formica rufa which I 

 obtained from Camberley ; he obtained the following results : 



1. Ten ants were shaken in a stoppered bottle, which was 

 rinsed out with water after the ants had been removed. The 

 amount of acid found in the bottle was less than '002 gm. 



2. Ten ants were dropped into boiling water to extract the 

 acid from them these 10 ants gave '021 gm. ( = '0021 gm. per 

 ant). 



3. Fifteen ants (six dead and nine alive) were treated with 

 boiling water these 15 ants gave '027 gm. ( = '0018 gm. per ant). 



He therefore concludes that each ant, on an average, contains 

 about '002 gm. (2 milligrams) of formic acid. 



F. rufa is an omnivorous feeder, devouring insects, carrion, 

 honey of flowers, honey-dew, the excreta of Aphidae, caterpillars, 

 etc. etc. 



The workers drag home to their nests both living and dead insects, 

 exploring every tree and bush in the neighbourhood, and are thus 

 of great value in clearing woods and forests of insect pests. It is 

 probable, considering how many insects, etc., the ants of a large 

 colony may be seen to bring home per minute on favourable days, 

 that they would bring in nearly one hundred thousand daily. 

 Forster in 1850 states that the rufa nests near Aachen were nearly 



