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Bumblebees

By Whitney Cranshaw, Colorado State University Cooperative Extension, Entomology

Public awareness of the honeybee declines has increased, and subsequently, so has the attention being paid to these pollinators.

There are over two dozen species of bumblebees (Bombus species) found in Colorado. Unlike honeybees they are native to the region and are extremely important pollinators of many native plants, perhaps being most obvious at alpine elevations. Bumblebees also are "buzz pollinators", which shake the flower as they feed on the nectar and making them extremely efficient at pollinating certain types of flowers, notably tomatoes. A substantial industry has developed providing bumblebee colonies for greenhouse tomato producers.

Bumblebees are social insects, but produce an annual colony. The overwintering is a large, mated female "queen". They seek protected areas during winter and issue out in spring looking to establish colonies. Most often bumblebees use abandoned rodent burrows for nesting. However, they sometimes are found in old mattresses, inside abandoned vehicles, or among insulation within walls. Regardless, nests almost invariably are established where there is insulating debris that is used in nest construction.

Initially, the overwintered queen does all activities required for colony development. Jug-shaped waxy cells are produced for rearing young and storing nectar and pollen. The queen forages for food and expands the nest as needed. The first young produced reflect this overtaxing, and are quite small due to their restricted diet. They assist with further colony development and subsequent bumblebees tend to be increasingly larger as more food is collected. During these early stages, allred-butted bumblebee (44021 bytes) bumblebees are female workers, not sexually competent because of the poor diet they received during development. It is usually only in late summer that the large, sexually mature "queens" are produced. Some males also are raised at the end of the season. The females mate and become the overwintering queens that will establish next year's colony. Workers and males die at season's end and the colony is abandoned.

Bumblebees can sting and will aggressively defend their colony, which unfortunately may be difficult to detect. Foragers, however, are quite passive and rarely sting unless severely provoked.

Four species of Colorado bumblebees have orange/orange-red markings on the hind end ("red-butted" bumblebees, shown at right) and some species (e.g., Bombus huntii) are very common.

Photos: Judy Sedbrook.

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Date last revised: 01/05/2010