ORDER VI. VEIN-WINGED INSECTS. 249 



over larkspur, borage, or other blue flowers, and discharge 

 any of their fluid substance upon them, their blue color will 

 be changed into red. 



In the ant-hills among the pine woods we very commonly 

 find little resinous cakes, formed like pebble-stones, which, 

 like other building materials, are carried into their dwellings 

 by the ants. This substance, saturated with the formic 

 acid, is very similar to the so-called frankincense, used in 

 churches as well as private houses as a perfume, because 

 when put upon lighted coals its smoke emits a pleasant, 

 amber-like odor, somewhat resembling that of frankincense, 

 but which is undoubtedly due to the presence of formic acid, 

 with which this resinous substance is impregnated by the 

 ants. The true frankincense (Olibanum, Libanus thuriferd) 

 is brought from Central India, and is obtained from the res- 

 inous juice of a tree called Browellia serrata. This resin 

 is used in India not only for its perfume, but as pitch, when 

 boiled with oil, for pitching the bottoms of ships ; and in 

 medicine for its stimulant, astringent, and diaphoretic prop- 

 erties. The formic acid was first discovered, about a cen- 

 tury ago, by the German chemist MarggrafF, in Berlin, 

 and it is now also artificially prepared by distillation for 

 medicinal purposes, as well as for its perfume when 

 burned. 



Many curious and interesting phenomena have been ob- 

 served in connection with the habits and customs of the 

 ants, a few of which we must notice in this place. In the 

 pleasant evenings of the month of August there are often 

 seen swarms of male and female ants rising in large col- 

 umns perpendicularly into the air, ascending and descend- 

 ing in large masses, and, after thus manoeuvring for a time, 

 they come down to the ground, lose their wings, and die, as 

 soon as the females have deposited their eggs in the hills 

 and left them in charge of the workers. These flying col- 

 umns of ants sometimes appear like a mass of thick smoke, 



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