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 (Olibareum, Libanus thurifera) 
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 Margeraff, 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 manceuvring 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, 
L2 
