Scientists studied 166 long-term surveys of various insects from 1,676 sites worldwide to track their populations which are slowly changing over time. They found that land-based insects especially flying insects like the butterfly are seeing a dramatic decline over 30 years, while marine-based bugs are thriving.
They hypothesized that the increase of water-based insects could be the result of a more environmentally friendly water policies protecting their habitats.
Land-based animals are declining in population
Global averages on the population of the insects show a significant drop although the number of insects being studied varied from place to place even in the nearby sites. The study shows that for the past 75 years, butterflies, grasshoppers, and other land insects had declined by 0.92% per year, said Dr. Roel van Kirk, the lead author of the research from the German Center for Integrative Biodiversity Research.
At this moment it might not mean so much but it actually means that in 30 years, we will see a 24% decline in their population, and 50% fewer in the next 75 years. The decline in their population happens quietly that we may not notice it, said the insect specialist.
You can compare it to the experience of going back to your hometown and find that everything has already changed, and all too often not for the better, Dr. Kirk said.
Windscreen phenomenon
Professor Jonathan Chase, another author of the paper said that their findings confirm the "windscreen phenomenon" in which fewer bugs get splatted on the windscreens of the cars than the last 30 or 40 years.
These flying insects have indeed decreased on average. However, most of the insects are less visible since the live out of sight, such as in the soil, in the water, or tree canopies.
They also revealed that these days there are fewer insects now living in the grass and the ground. But on average, insects living in the tree canopies has stayed roughly the same.
The land-based insects may be declining, but their cousins under the water seems to thrive as they show an average increase of 1.08% every year. That means we can expect a leap of 38% over 30 years for water-based insects.
Not too late to reverse man-made effects
The results of their study show that it is not yet too late to reverse the effects of humans on bugs. As we continue to make efforts in saving our waters such as conducting clean-up drives, we can save organisms also living in them.
This method makes scientists and conservationists hopeful for the insects, according to their paper published in the journal Science.
Ann Swengel, a co-author of the study, has spent the last 34 years studying the population of butterflies across Wisconsin and nearby states in the US, said that although there is a decline in their population, she also saw that in some sites, they are able to do well.
She added that it takes a lot of years and data to understand the failures and successes, species by species, and site by site. Although it is beyond the control of any person, our choices can make a difference in saving the insects in each site.
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