ABOVE: The Luquillo rainforest of Puerto Rico

Since the 1970s, populations of arthropods—a group of animals that includes exoskeleton-bearing critters such as insects, spiders, centipedes, and millipedes—in the Puerto Rican rainforest have drastically fallen, according to a study published Monday (October 15) in PNAS. 

Rensselaer Polytechnic University biologist Bradford Lister first collected data about arthropod biomass in Puerto Rico’s Luquillo rainforest in 1976. He and coauthor Andres Garcia, a biologist at the National Autonomous University of Mexico (UNAM), repeated the measurement in 2012 and found that it was 10 to 60 times smaller than it was 36 years earlier, according to a press release. That’s a decline of 99 percent, according to Science.

Also during that period, the temperature in the forest rose by 2 °C (3.6 °F). Lister tells The Washington Post that according to their analysis,...

The new study is one of many documenting declines in insect populations. For example, a 2017 study reported that in protected areas in Germany, insect biomass had decreased by 76 percent between 1989 and 2016. 

The researchers saw a decline not only in arthropods in Puerto Rico but also in animals that eat arthropods. For instance, the population of anole lizards, which eat insects, had dropped by more 30 percent since the first sampling, the Post reports. 

“This study in PNAS is a real wake-up call—a clarion call—that the phenomenon could be much, much bigger, and across many more ecosystems,” David Wagner, an invertebrate conservation biologist at the University of Connecticut, tells the Post. “This is one of the most disturbing articles I have ever read.”

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