WHY DO THESE BEES STAB PLANTS?

 We know a lot about the way bees and other pollinators impact our lives. We have to because without them we Wouldnt have things like almonds and apples and blueberries. Yet there is something we have completely missed about the humble bumblebee. And it might give them a leg up in weathering climate change. In a paper published in 2020 in the journal Science, researchers reported a previously undocumented behavior in bumblebees. 

In tough times, when the colony is hungry, bumblebees will use their mouthparts to deliberately damage the leaves of plants that haven't yet flowered which seems like a bad idea when you need those plants for food. The researchers observed the bees and concluded that they’re not consuming pieces of the plant or taking them back to their colonies. Instead, they appear to be damaging leaves because it induces the plant to flower sooner. The researchers found that bee-damaged plants flower up to thirty days earlier than plants that have not been stabbed by bees. What’s more, they gave one test colony access to flowering plants and another colony access to flowerless plants.

 They found that the leaf-damaging behavior was strongly associated with bees who were presented with the flowerless plants. This behavior makes sense. The colony depends on flowers for food, and if you’ve got a lot of baby bumble bees to feed, you can’t afford to wait for those slacker plants to get their flower on. What we don’t know is how this leaf-stabbing behavior evolved. It seems unlikely that individual bees would have learned that puncturing a leaf causes the plant to flower early since so much time passes between the behavior and the reward. 

Neither are they looking for pollen in the wrong places -- bumble bees instinctively know better than that. We’re also not really sure why the leaf-stabbing behavior works. It could be that the plants interpret the behavior as an attack by actual leaf-eating bugs, so they flower sooner as a survival strategy. But... there aren't really any known examples of plants doing this when, say, grasshoppers arrive, so it doesn’t seem likely. Neither is early flowering advantageous for the plant. It’s more beneficial for plants to flower at the same time as other members of their species, in order to ensure cross-pollination. However, scientists conducting this study did find a clue… by indulging in some leaf-stabbing themselves. And they found it's not just the physical damage that induces flowering. Plants damaged by actual bees still flowered up to twenty-five days sooner than plants damaged by researchers. 

So it’s got something to do with the bees themselves. It could be that they’re injecting some kind of chemical into the leaf that jump-starts flowering. But we’d have to identify that chemical to know for sure -- and it could be something totally different. Ultimately, though, this clever strategy might give bumblebees a head start on adjusting for climate change. As the climate warms, it may become more common for the calendars of plants and pollinators to be out of sync. And that means that many pollinators won't able to find flowers when they need them the most. But pollinators that can change the flowering schedule of their food source will likely have an advantage over species that have to wait around for nature to take its course.