University of Otago geneticist and bee researcher Associate Prof Peter Dearden made the comments amid concerns on social media.
Some concerned Facebook users were worried a virus could be spreading through the population.
Others have been feeding dying or struggling bumblebees sugar water or honey.
Prof Dearden said the large number of dead bumblebees was probably because the population was higher than normal.
"I think we are just seeing lots of dead bees because there are lots of bees,'' Prof Dearden said.
The short-lived creatures often struggled as the temperature dropped.
Many would be dying because they had reached the end of their natural lives, but some could be rescued if they were simply lacking the energy to make it back to their nests.
"Many of those are probably rescuable if you give them some sugar water or diluted honey.''
There was no evidence the increase in dead bees was caused by a virus, as he had not seen any devastated nests - which would be where the bees would probably die if they were hit by a virus.
However, a small portion of bumblebees might by dying after reacting to certain plants.
"Lime trees, in particular, seem to have lots of dead bumblebees and lots of dead honeybees around them.''
