What causes a plague of Locusts?

I found this great quote in the Health and Science section of the February 13th 2012 issue of Time magazine on page 18. Begin quotes.

Genesis of a plague cycle

In an outbreak year, locust swarms
blanket 20% of the Earth's surface. Why?
Blame agricultural practices like overgrazing.

1. Eroded Soil
Overfarming and overgrazing
deplete nitrogen from the soil.

2. Protein shortfall
Plants growing in low-nutrient soil
contain less protein

3. Locust hordes
Locusts prefer the low protein
flora and swarm to feed on them
end quote from Time Magazine
 
It's always interesting when plagues like one hears about in the Bible are explained scientifically. If I extrapolate, it sounds like when too many people are trying to feed themselves from a given farming area it creates a plague cycle. So, then the plague cycle happens and a whole lot of people in that area starve to death when the locusts are done feeding because there is no food left to eat in the fields.