A Bumble bee on Mountain Mint. (photo by Don Hunter)

Bumble bees lead a precarious life. They have annual
colonies, i.e., the colony only lasts one season. At the end of the season the
entire colony, except for the fertilized females (the queens), dies. A queen
overwinters in a sheltered location and emerges the following spring to found a
new nest. How does she know when to emerge? The cue she uses is the soil temperature. But as the climate warms the soil will warm earlier and earlier, so a bumble bee queen will start to establish a new nest earlier and earlier. To establish a new nest the queen must be able to find a
source of pollen to feed her young larvae. This means that she must have a
supply of flowers available. But flowering is controlled by the length of day,
which does not vary with the temperature. This creates a problem for the early
emerging bumble bees. If there are no flowers open then there is no pollen to
feed her young.

A new publication in the journal Science reports that bumble
bees punch holes and bite the leaves of plants that have unopened flower buds.
Plants that receive this treatment bloom as much as a week earlier than plants
that received no bites. 

The researchers attempted to mimic the bites by punching
holes in the leaves of plants with tweezers and razor blades. They found only a
slight decrease in time to flower, implying that it is not the damage that
causes earlier flowering. It must be something transmitted in the bee salivary
secretions. 

It seems there is always something new to discover in nature.