Managed bee populations decreased by more than 40 percent between 2014 and 2015, and in 2013 the bumble bee population dropped by 35 percent.
As climate change kills off some of their favorite flowers, several bumblebee species in the Rocky Mountains have responded to those losses by evolving shorter tongues.
Researchers have now found one more piece of the puzzle: Bumble bee tongues are shrinking.
The researchers are concerned about what this decline could signal for larger trends across bee populations and flower ecosystems. The result is that the bees are still doing fine with their shorter tongues. But because the flowers where the long tongue is required have dwindled, the bees didn't need that much tongue.
Declining honey bee populations would affect up to 75 percent of domestic produce, Greenpeace reports, with apples, strawberries, tomatoes, and almonds among the hardest-hit crops. One possibility is that the bees are just getting smaller.
A U.S.-Canadian research team found that deep-tubed flowers are blooming less often on the slopes of three Rocky Mountain ridges in Colorado, changes linked to increasingly warmer summers. This forced the bumble bees to feed on shallow flowers. The shortening of bee tongues was documented by the researchers by measuring the length of bee tongues in preserved specimens from 1966 to 2014.
What they discovered is that two bee species in the region, Bombus sylvicola and Bombus balteatus, have shorter tongues than they did 40 years ago.
It is very surprising that in the rather short period of less than 50 years, an insect is adjusting the way it's body grows. That evolution, it turns out, could be an important aspect of bee survival in the face of changing climates.
The pattern seen here may predict future effects of climate change in other systems, the authors say. Climate change is to blame, Miller-Struttmann says.
More than 85% of flowering plants - including some crops - require pollinators to reproduce. Furthermore, as the planet continues to warm, bee tongues will continue to shrink, the researchers say. The economic value of bee pollination services ranges from $10 billion to $15 billion.
The results highlight how certain mutually beneficial ecological partnerships can be lost due to shifts in climate. But for now, it's still unclear how the flowers will be affected. The costs of sporting long tongues now seem to outweigh the benefits, so natural selection has favoured bees with shorter tongues.
These problems appeared not only in Colorado, where the study was conducted, but in other places as well.
While biologists have tracked how global warming has altered the developmental, migration, timing and other behavior in plants and animals, what makes this study unusual is the physical changes in the bees, said study co-author Candace Galen at the University of Missouri.