While temperatures in the tropical forests of northeastern Puerto Rico have climbed two degrees Celsius since the mid-1970s, the biomass of arthropods – invertebrate animals such as insects, millipedes, and sowbugs – has declined by as much as 60-fold, according to new findings published today in the Proceedings of the National Academy of Sciences. While temperatures in the tropical forests of northeastern Puerto Rico have climbed two degrees Celsius since the mid-1970s, the biomass of arthropods – invertebrate animals such as insects, millipedes, and sowbugs – has declined by as much as 60-fold, according to new findings published today in the Proceedings of the National Academy of Sciences.