MIGRATING CRANES fly over northern Israel earlier this month.
(photo credit: REUTERS)
A study of the migration of insects, especially in colder weather, found that it is the largest overland migration on Earth. The 5.3 trillion migratory insects in the UK alone that travel south each year to Africa constitute a biomass of nearly eight times that of traveling birds. Scientists worry, however, that global warming will significantly increase the number of migrating insects, which can impair many ecosystems.
Where do the insects disappear to during the winter? Dr. Nir Sapir of the University of Haifa’s evolutionary and environmental biology department, lead author of the study, noted that until now there has not been a comprehensive, quantitative study on the phenomenon of insect migration. “We hypothesized that there are many populations of migratory insects, but it was not known which migrate and which do not, when it happens or how far they go,” he said.
The large-scale international study, which included researchers from the University of Haifa, Nanjing University, Exeter University, the Hebrew University of Jerusalem, the University of Greenwich and Rothamsted Research (both in the UK), is now changing this field. To collect the data, the team set up radar systems 15 years ago in southern England, covering an area of 70,000 square meters.
They measured the weight of insects, altitude and other data.
For very small insects, which weighed less than 10 milligrams and were not picked up on radar, they used special nets that caught them in the air. Data were collected between 2000 and 2009 on insects that flew over 150 meters above the ground, unlike mosquitoes, house flies or honeybees, which fly much lower and were not included in the study.
The findings clearly showed that in the fall, there is movement of these insect populations to the South, and in the spring there is movement to the North. The scope of the insect exodus surprised even the researchers – about 5.3 trillion insects, which created the biomass of 3,200 tons, roamed every season. The study did not examine the points of origin and destination of the entire population of insects, but the researchers believe that migration covers at least several hundred kilometers and possibly much more.
“Because there is evidence that this migration also occurs above the sea, and because Britain is an island, the insects have reached the mainland in the spring, and at least some of them reach the mainland also in the fall,” Sapir said.
Another finding, which was no less surprising, was that the insects are helped by the wind to reach their destination and choose to “hitch a ride” on specific gusts of wind. Insects survived the southerly winds in spring and northern winds in the autumn.