Where Are All The Flying Insects Going? Researchers Observe A 75% Decrease In The Amount Of Flying Insects Over The Past 27 Years
Today lets talk about bugs.
Icky, icky, give me the shivers, bugs.
But rather than a cute post about a bug I found outside, lets talk instead about a recent publication from the journal PLoS One titled "More than 75 percent decline over 27 years in total flying insect biomass in protected areas."
In this publication, the researchers spent an very long time studying flying insect population biomass (the studies were done from the years 1989 to 2016) at a large number (96) of different locations all across Germany. The point of these studies were to get a better handle on how insect populations change, depending on where they are located relative to human habitation.
There have been a variety of studies performed in the past which have indicated that insect populations have been on the decline. With extensive studies having been done on insects that are important for plant pollination like bees (, ) and the hawk moth, all showing that the populations of these insects are in decline. 
These decreases pose a problems for both we humans as well as the ecosystems of our planet as a whole, as pollination is absolutely essential for plant growth and maintenance of the habitats in which the many organisms that inhabit the planet live. It's also essential for food production, and I don't know about all of your opinions on eating, but I really like doing that and would like to continue to!
Onto The Research
The scientists conducting this study were monitoring flying insect populations and to do this they used Malaise traps, which to my untrained eye just looks like a tent made of mesh. These traps catch the flying insects, the amounts and identities of which can then be painstakingly calculated and determined (likely by some graduate student or unpaid intern).
Most of the 92 locations where the data was generated from were only sampled one time, one year and were not returned to in subsequent years. The sampling was done about every 11 days after the trap was set up (in the spring) and over the course of the whole study the researchers collected over 1500 samples. It is from these bug samples that the data is generated.
What Did They Observe?
They saw a significantly negative relationship between the overall biomass of insects relative to time. The authors state that there was a 6.1% decrease in biomass on average, PER YEAR, over the duration of their study. This is reflected in the figure to the left. Here what we are looking at is the average number of grams of insects caught in the traps, per day relative to the years that the study went on. Looking at these box plots we can first state that the error is huge, but that seems reasonable as collecting insects likely has a lot of sample to sample variation. However we can also see a VERY clear trend with regards to the average value and this trend goes down by quite a lot over the years.
The researchers further quantified this data and looked at when this decrease was happening. They saw that the observed loss of biomass disproportionately occurred in the summer months when the insect population should have been at its highest, and was less pronounced in the spring and fall. We can see this in the plot to the right where most of the change occurs in July and August.
The researchers explored their data looking for discrepancies between the various sampling locations, but found the trends held for the general regions in which the samples were obtained. The authors discuss that depending on the area that the samples were taken there were always more or less insects (marshy wetlands had more then say a sandy area with fewer nutrients. However the general decline in the insect populations were consistent in both areas, relative to the total amount of insects that these areas supported. Meaning, the decrease wasn't just because of one type of ecosystem, it was everywhere.
They also searched for explanations like weather conditions and found that parameters like temperature or amount of moisture were unable to account for the decreases they observed.
The authors summarize stating that over the 27 years in which the flying insects were studied, a decrease in total population of around 76% was observed. Their results here mirroring that of previous studies on bees, and moths that I mentioned before, but expanding upon that data indicating that the issue is not limited to just these pollinators but to ALL flying insects.
What Does This Mean?
They don't know!
One of the prevailing theories put forth to explain why bee and moth populations were declining was climate change. . They make it clear that their data does NOT support climate change as the cause for this phenomenon, nor does it support that changes to the landscape itself are affecting the insect populations.
They state in their discussion that the rate of decline in the insect population they observe here is "alarming," and stress the urgency in quickly figuring out what the true cause is, as well as better understanding just how quickly this will be affecting ecosystems as a whole.
Flying insects appear to be dying, and their populations are dwindling quite quickly. Additional research is needed to figure out the why, all we know now is what is happening. Hopefully data like this stokes the fires for researchers and we can identify the culprit. Allowing for a solution to be put in place, before it is too late and ecosystems are irreparably damaged.
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