The Dilemma of Insect Counting: More and more land is used for agriculture, which means more pesticides are used and fewer diverse crops grow. In addition, cities are growing, which is why forests and other wilderness areas are declining. All of this leaves insects with fewer places to shelter and pollinate. Added to this is climate change, which is causing them problems. This is proven by numerous studies from all over the world.
Complete species censuses would therefore be very time-consuming and costly. Nevertheless, the study shows clear tendencies. They conducted studies in six different habitats, ranging from coastal to mountainous regions. The western bumblebee, formerly one of the most common species in California, has not been found at any of these sites. In addition, there is a large number of worldwide studies, all of which show that insect populations are declining. So scientists cannot say for sure how many animals of a species still exist. However, you can prove that the total stock is declining.