336 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
of what locusts are and how they live. A locust is nothing but a spe- 
cies of grasshopper, but usually larger in size and characterized mainly 
by gregarious habits. 
The life cycle of locusts and grasshoppers is fairly simple. The 
eggs are deposited by the female in the soil, in packets, or “egg-pods,” 
each containing 30 to 100 eggs. In countries with a cold winter, eggs 
lie dormant throughout this season, and in spring the young locusts, 
or “hoppers,” emerge from them onto the surface of the soil. In the 
Tropics, the eggs may hatch in 2 to 3 weeks, if there is rain or moisture 
in the soil. The difference between grasshoppers and locusts becomes 
apparent in the hopper stage; the former may be numerous, but each 
one lives independently of the others, whereas the latter congregate 
in dense groups, or bands. Further development consists in rapid 
growth, stimulated by voracious feeding on green vegetation, and in 
the periodic moulting which occurs 4 to 6 times before the adult insect 
appears; these differ from the hoppers only in size and the presence 
of two pairs of wings. The whole cycle occupies a year in temperate 
climates, but in the Tropics there may be several generations within a 
year. 
The most striking feature in the behavior of locust hoppers is their 
mass movement in bands, which may cover several square miles. The 
relentless march of hopper bands which are not stopped by obstacles, 
even by water, creates an impression of a dark purpose, of a movement 
toward an objective, and many more or less fantastic explanations 
have been offered to account for it. Recent investigations have, how- 
ever, definitely proved that the movement of hoppers depends very 
largely on temperature and occurs only on sufficiently hot days, while 
excessive heat again causes it to stop. The hopper movements are not 
caused by hunger and do not aim at finding food, since hoppers, driven 
by heat, often leave a fertile area and march into open desert. 
When hoppers become adult and acquire wings, they soon begin to 
fly about in swarms. Again, a swarm does not leave an area because 
of lack of food, and it does not necessarily fly toward more fertile 
lands, but its flight is initiated, directed, and interrupted by various 
weather factors. Swarms may reach great size and contain fantastic 
numbers of individuals. Thus, a swarm in East Africa measuring 
3 by 60 miles was estimated to consist of a million million locusts; and 
even larger swarms are on record. 
The distances covered by swarm flights may be enormous. In 1693, 
swarms of the migratory locust from the Danube delta reached Wales, 
at a distance of about 1,600 miles in a straight line, though probably 
not in a single flight. A swarm of the desert locust was encountered 
in the Atlantic midway between South America and Africa, about 
1,500 miles from the latter, whence it certainly came. This must have 
