Bumble Bees

From Bugwoodwiki
Hpipm banner 800.jpg

Compiled by Whitney Cranshaw, Colorado State University:

Colorado Insects of Interest

Bumble Bees

Figure 1. Foraging bumble bee with filled pollen baskets on hind legs.

Scientific Name: Bombus species

Order: Hymenoptera (Bees, Wasps, Ants, Sawflies and Relatives)
Family/Subfamily: Apidae/Bombinae (Bees/Bumble Bees)

Figure 2. Bumble bee (top) compared to a honey bee (bottom).
Identification and Descriptive Features: Bumble bees are large, heavy-bodied and quite fuzzy bees. Although most North American species of bumble bees are black and yellow, orange markings occur on several species found in Colorado. The most common species in much of the state, Bombus huntii, has a large band of orange on its abdomen and most of the species that are restricted to higher elevations of the state have some orange markings. The largest species in the state, B. morrisoni and B. nevadensis, are primarily yellow. Size among all species varies considerably with production of large queens and some quite small workers.

Distribution in Colorado: At least one of the 23 species of bumble bees (Table 1) present in Colorado can be found any where in the state. Among those that have the widest range within Colorado are Bombus huntii, B. appositus, B. morrisoni, and B. nevadensis. Several are found primarily at higher elevations, including Bombus balteatus, B. bifarius, B. centralis, B. melanopygus, B. rufocinctus, B. sylvicola.

Life History and Habits: Bumble bees are social insects that establish colonies which last through a growing season. Colonies are initiated in spring by an overwintered and previously fertilized female, known as the queen. As the colony develops and expands it may ultimately be populated over 100 individuals that are organized into different castes. Dominating are infertile females, known as workers. By midsummer some males are usually produced along with some large females, which will serve as potential queens of the following season. The original queen, along with all workers and males perish at the end of the year.

Figure 3. Interior of a bumble bee nest showing wax cells, many of which are capped and contain pupae. The species is Bombus vagans, not present in Colorado. Photograph courtesy of the Ken Gray Collection, Oregon State University.
Bumble bee colonies are established in cavities, usually with some sort of insulating material present. Abandoned rodent burrows and bird nests are common sites for nest construction. They have sometimes been observed to nest among stuffing of old couches, in insulation inside the body of long unused cars, and similar sites that provide the protection and space they seek.

Within the colony, rearing and food storage occurs in roundish wax pots that are spread throughout the nest space. The wax produced from abdominal glands by the bees and the jug-like cells are often being reformed to meet colony needs. Eggs are laid in these wax pots and the larvae develop within them, being fed and tended by adult bees. When full-grown the larvae cap over the rearing cell with silk and pupate, later emerging as a winged adult.

Nectar and pollen serve as the foods that sustain the bumble bee colony and forager bees collect the pollen on the hind legs, in specialized pollen baskets, similar to honey bees and digger bees (Family Apidae). Excess food will be stored for later use but bumble bees do not produce large amounts of honey (processed nectar) and ultimately use all food that is collected.

As the colony develops through the season several changes in the colony occur. Originally there is a single queen that is charged with all colony functions - from nest construction to food collection as well as rearing. Subsequently the first workers produced tend to be rather small because of poor diet, and size contrasts markedly from the queen. However, as the workers assist with and take over most colony functions the larvae are increasingly well fed and subsquently develop into larger workers.

Figure 4. Overwintered queen of Bombus morrisoni.
The colonies are usually sufficiently well established by midsummer that some males are produced along with some large and potentially fertile females, potential queens. Males spend most of the time outside the colony in roosts established at prominent points. Virgin fertile females that pass are pursued by the males for mating. Male bumble bees can be distinguished from the females by having substantially larger eyes; they also lack a stinger.

Bumble bee females can sting and workers will readily defend a colony if it is disturbed. The sting is quite painful but, unlike honey bee workers, bumble bee stingers do not detach and they are capable of repeated stings.

Bumble bees are very important in providing pollination services to many plants. They have a different approach to pollen collection than do honey bees and most other bees, known as “buzz pollination.” When visiting a flower a bumble bee will often grasp it with its mandibles and vibrate, causing the pollen to be shaken out onto its body. Such pollination style is critical for many native plants which are dependent on bumble bees for pollination and subsequent seed production.

Among the plants that are dependent on buzz-pollination are many plants in the nightshade family (Solanaceae). As a result, bumble bees are used widely in pollination of greenhouse-grown tomatoes and peppers, which are produced commercially in several areas of Colorado.

Cuckoo Bumble Bees: Among the native Colorado species are three cuckoo bumble bees (subgenus Psithyrus). Queens of cuckoo bumble bees enter and displace the queen of existing colonies and the workers then rear the young of the invader. The cuckoo bumble bees are usually distinguished from other bumble bee species by having an abdomen that is less hairy. The most common species, Bombus (Psithyrus) insularis Smith, is also one of the lighter colored species.

Figure 5. Size range of Bombus huntii. An overwintered queen is on the left.
Figure 6. A commercial bumble bee hive used in pollination of greenhouse-grown tomatoes.
Table 1.  A checklist of bumble bee species (Bombus) present in Colorado, arranged by subgenera (in parentheses).  Notes on distribution provided by Virginia Scott, University of Colorado.


  balteatus - high elevation over 10,000 ft
  auricomis (sometimes considered a subspecies of nevadensis) - Eastern CO
  nevadensis nevadensis - Our biggest species. Found throughout most of the state roughly 5000-8000 ft
(Bombus s.str.)
  occidentalis – formerly common from the Front Range west.  Decreased populations of     this species have been noted in several western states
  fraternus - Front Range and eastern Colorado up to about 6500 ft
  riseocollis - across state at lower elevations (<6000 ft)
  morrisoni - across state at lower elevations (<6500 ft)
  ufocinctus – Front Range-west below about 8000 ft
  fernalde - about 7000-8500 ft
  insularis - across state (4500-11,000 ft)
  suckleyi - mountains (6500-10,000 ft)
  bifarius - mountains (7500-10,000 ft)
  centralis - mountains (7000-9000 ft)
  flavifrons - mountains (8500 - >12,000 ft)
  frigidus - over 10,000 ft
  huntii - across state 5000-7000 ft, not along eastern edge of state
  sylvicola - mountains over 10,000 ft
  melanopygus - mountains roughly 9500-12,000 ft
  mixtus - mountains roughly 9000-11,000 ft
  appositus - across state between (roughly) 7500-10,000 ft
  californicus (sometimes considered a subspecies of fervidus) - 7500-10,000 ft
  fervidus fervidus - lower elevation 5000-8000 ft

pensylvanicus - lower elevations, mostly eastern plains up to 6000 ft; valid Moffat and Delta county records

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.