DESCRIPTIONS OF MOVING SWARMS. 
95 
ing forward in the same way; a movement which the writer of this chap- 
ter has observed on a small scale. 
Denon, 192 speaking of a flight he observed, says: 
Information was brought that the plain was covered with birds, which traveled in 
close phalanxes and descended from the east to the west. From a distance they actually 
saw that the fields seemed to roll along the plain in the direction mentioned. Instead 
of birds, they found a cloud of locusts, who only skimmed along the land, stopping at 
every blade of corn to devour it and then flying to fresh prey. 
The following description of their movement by the traveler Anders- 
son is worth repeating 193 : 
The several columns that crossed our path in the course of the day must each have 
been many miles in length and breadth. The noise of their wings was very great, 
not unlike that caused by a gale of wind whistling through the shrouds of a ship at 
anchor. It was interesting to witness at a distance the various shapes and forms that 
these columns assumed, more especially when crossing mountain ranges. At one time 
they would rise abruptly in a compact body, as if propelled by a strong gust of wind: 
then, suddenly sinking, they would disperse into smaller battalions, not unliko vapors 
floating about a hillside at early morn, and when slightly agitated by the breeze ; or 
they would resemble huge columns of sand or smoke, changing every minuto their 
shape and evolutions. 
During their flight numbers were constantly alighting ; an action which has not 
inaptly been compared to the falling of large snowflakes. 
The Italian author Lucretiis, from whose paper we have already fre- 
quently quoted, makes the following statement in reference to their 
movements : 
Upon the emigration of locusts, certain circumstances, as common as they are un- 
heeded, merit the attention of the observer. Their flight is more certain, and at a 
greater altitude, whenever the atmosphere is of a heated temperature, and the air 
clear and calm (?)• On the other baud, when the atmosphere is charged with mist or 
with rain, or pervaded by a chilly element, or oven about the rising or the setting of 
the sun, they move more slowly, exhibiting a certain rigidity, moving their wings with 
difficulty, and not rising to any great height. And when they attempt to continue 
their raids in a rainy season, or one tending to cold, they begin by agitating their 
wings and exerting all their strength to rise; but not finding themselves in a condi- 
tion to sustain a long journey, they at first droop, and then fall precipitately to the 
ground, and are compelled to continue their journey on foot. 
Bowles, 191 who believes the chief cause of their migration is the flight 
of the females to avoid the importunities of the males, says : 
In their efforts to escape they begin to rise little by little into the air, and finally to 
the height of 400 or 500 feet, forming a cloud which intercepts the rays of the sun. 
The clear and serene sky of Spain is obscured and becomes in the midst of summei 
more dark and gloomy than that of Germany in spring. The rustling of so many mill- 
ions of wings forms a dull roar similar to that which a sudden blast of wind produces- 
in a forest full of leafy trees. The route which the first formidable swarm takes always 
follows the wind, and this first flight is usually prolonged about two leagues, but if 
the weather is calm and serene the length of their flight is less. In these fatal pauses 
the locusts commit the most frightful ravages. By their exquisite sensibility to odora 
they scent from a great height in the air a field of grain or a garden. I have seen 
them turn from the course of their march more than a half a league obliquely to de- 
192 Travels in Upper and Lower Egypt, Eng. Trans. 
193 Lake Ngami, 282. 
194 Introduziono alia Storia Nat. ot Geog., flsica Spagna, T. 2, pp. 1-24. 
