There are many stories in the news lately
about the deadly locust invasions, especially in Africa. Locusts
belong to the same order as grasshoppers, katydids, and crickets
- the Orthoptera (derived from the Greek words orthos meaning
straight or rigid and ptera meaning wing).
Grasshoppers congregate
in huge swarms that can do severe damage to crops. These
swarming grasshoppers are called locusts. There are more than
20,000 species of grasshoppers known to science, but only about
a dozen of these transform into locusts and produce damaging
swarms.
Locusts and
grasshoppers are the same in appearance, but locusts can exist
in two different behavioral states (solitary and gregarious),
and most grasshoppers do not. When the population density is
low, locusts behave as individuals, much like grasshoppers.
However, when locust population density is high, individuals
undergo physiological and behavioral changes, known as phase
polyphenism, and they form gregariously behaving swarms of
adults.
In addition to changes
in behavior, phase change may be accompanied by changes in body
shape and color, and in fertility, physiology, and survival.
These changes are so dramatic in some species that the swarming
and non-swarming forms were once considered to be different
species. The scale of population increase and migrations also
distinguish those species known as locusts from grasshoppers.
Locusts are large
herbivorous insects that can be serious pests of agriculture due
to their ability to form dense and highly mobile swarms. They
are species of short-horned grasshoppers that periodically form
large populations in dense migrating groups, where individuals
differ in several characteristics from those living separately.
A locust has longer and stronger wings and a smaller body than a
grasshopper.