The Ecology of Bumble Bees

Ecological constraints

Bumble bees are much better adapted to survival in cooler latitudes than the honey bee. Summer survival depends on whether foraging bumblebees gain more energy from the nectar than they use up visiting the flowers. Bumblebees overcome the problem of winter food shortage by shutting down the colony until spring. So when bumblebee queens emerge in the spring the success of the new colony rests entirely on their shoulders.

This makes them hairy !

Bombus jonellus male

First the new queens must find a nest site, then collect as much food as possible to feed the young bumblebee larvae. They have to be able to fly in all weathers – so a clear advantage in an unreliable climate is a warm, hairy coat for insulation. A thick, water repellent coat allows bumbles bees to forage in the rain and late into the evening. The downside of a thick coat is of course, overheating and so no bumblebees live in hot tropical climates.

Machair grassland – plentiful flower resources but unreliable weather – good bumblebee habitat

A Scramble For Forage

Unlike honey bees that have evolved to take advantage of a ‘boom and bust’ availability of flower sources which favours insects that can move quickly to new nectar sources in a generally unspecialised way. In the cooler conditions that they are adapted to, the bumble bees survival strategy is more specialised. In temperate climates, especially where open grasslands dominate, flowers tend to have longer flowering periods. They are often small but there are lots of individual flowers. When they are grazed new flowers are produced giving a reasonable constant, if sometimes unpredictable flowering resource. The overall pattern in highly seasonal and this favours the annual nest and overwintering queen system of bumblebees rather than the long lived social system of the honeybee.

Nest Site Availability

In order to survive the winter honeybees are adapted to using cavities such as caves or hollow logs and in modern times, man made beehives. By contrast, bumblebee queens don’t need to look for long lasting nest sites and most species utilise old, small-mammal nests that are plentiful in grasslands. Of course, for all species of bees, if forage sources and nest sites disappear so do the insect species that depend on them along with their vital pollinating services.

Adapted from an original article by Mike Edwards of the Bees, Ants and Wasps Recording Society that appeared in Beecraft Feb 2005.

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