Bird migration is well documented by researchers the world over but insect migration is less known. Now, an international study found that not only do flying insects migrate on a seasonal basis but that this movement constitutes the largest migration in today’s world, creating a mass that is almost eight times that of birds that migrate from Britain to Africa.
In a study recently published in the journal Science, researchers examine the phenomenon of insect migration.
“The migration of 3.5 trillion insects, with a biomass over seven times that of the birds that migrate from Britain to Africa, has significant ecological ramifications. Insects are highly sensitive to climate change, and this may lead to dramatic changes in the population of migrating insects, causing important environmental changes,” says Dr. Nir Sapir of the Department of Evolutionary and Environmental Biology at the University of Haifa, one of the authors of the study.
Although flying insects constitute one of the largest populations on the planet, no comprehensive quantitative study has been undertaken until now. Researchers assumed that many insect populations migrate, but did not know which insects do so, when, and how many.
A broad-based international study undertaken by researchers from the University of Haifa, Nanjing Agricultural University, the University of Exeter, the Hebrew University of Jerusalem, the University of Greenwich, and Rothamsted Research is now providing a picture.
In order to collect data, radars were installed some 15 years ago in southern England. Data from these radars were used to estimate insect bio-flow over an area of 70,000 square kilometers. The radars measured the weight of the insects, their flight speed and their direction and height. For very small insects that weigh less than 10 mg and are not picked up by the radar, special nets were used to catch samples in the air. Between 2000 and 2009, data were collected for insects flying at heights of over 150 meters.
The findings clearly showed a southward movement of these insect populations in fall and a northward movement in spring. The researchers were surprised by the scale of this phenomenon: some 3.5 trillion insects, creating a biomass of 3,200 tons, migrated in each season.
The study did not examine the starting points and destinations of each insect population, but the researchers believe that this migration takes place over distances of at least several hundred kilometers and possibly even more.
“Since there is evidence that this migration also takes place over sea, and since Great Britain is an island, these insects must have come to Britain in the spring, and at least some of them must reach continental Europe in the fall,” says Sapir.
Also surprisingly, the data also showed that insects use the wind in order to reach their destination, choosing to “hitch a ride” on specific wind flows. The insects exploited the southerly winds in spring and the northerly winds in the fall.
“They actually chose the direction they wanted to go in. We were surprised to find that insects make conscious use of navigation capabilities in order to reach their destinations using these winds,” says Sapir.
The study’s authors say these findings have ramifications for many ecosystems, and even for our own everyday lives. In most cases, insects’ bodies include 10 percent nitrogen and one percent phosphorus. This makes them excellent fertilizer for plants and crops and nutritious food for insect eaters, such as birds, bats, and other animals.
“Such a large biomass has tremendous importance for the functioning of diverse ecosystems across large parts of the globe, and for other aspects of our daily lives,” says Sapir. “Cycles of nitrogen and phosphorus in nature are extremely significant, particularly since these chemicals form a limited component in the food chain. This massive movement of insects transports these vital materials across enormous distances.”
Researchers pointed out that the warmer the weather, the more insects are born.
“We do not know yet whether all types of insects are reproducing more, or whether only certain types are doing so. An increase in the number of some insects could be harmful, while in other cases it could actually be beneficial. Accordingly, it is too soon to tell whether this change should be welcomed. But what is certain is that this is the largest and most influential continental migration in the world, as far as we know to date. We need to start monitoring it carefully,” says Sapir.