A Color Based Dichotomous Key for Bumble Bee Identification in Washington State, v 1.1

A dichotomous key is a series of paired questions, the answers to which determines which couplet of questions to go to next--until the key predicts a species identification or other end point.

The dichotomous key is a common tool to assist in plant and animal identifications.

This key may not work as well in other parts of North America

Some interpretive notes:

How to use this key:

If this is your first rodeo, then start at the beginning.  The concepts of males and cuckoos are good to have a feel for when going out to observe. 

Using the key from the beginning is also a good way to encounter and learn the various technical terms for bumble body parts (e.g., scutum, stergite).  The colored blocks on the right hand side can be clicked on to get more information about the particular bumble bee part in question.

Another early objective is gaining confidence in which bumble bees show a corbiculum (pollen basket).

Once you have used the key a couple of times and are confident your bee in question has a corbiculum, it may be faster to jump down to the portion of the key most likely appropriate.  Those groups are:

Step

Description

Go to #

Comments or link to diagram or species page

Separating Females from Cuckoos and Males

 

1

Corbiculum / pollen basket present

5

1′

Rearmost leg hairy, rounded.  No pollen basket

2

Cuckoo Queens vs. all males

 

2

Heavy bodied cuckoo queen, very sturdy

3

2′

Any individual bumble bee with a hairy rear leg, lacking a pollen basket that is not a cuckoo queen

ID

This key is restricted to queens and female bumble bees at this time.  You can start the key at Step 5–if the male (drone) is similar to the queens or workers the key may be of assistance.

Separating Cuckoo Queens

 

3

Abdominal T4 has black center notch

ID

3′

T4 without black notch

4

4 (3′)

T4 yellow, T5 all black, occiput with yellow hairs

ID

4′

T5 with some yellow, black notch on T5, occiput with mainly black hairs

ID

Starting all non-cuckoo bumble bees

 

5 (1)

White on EITHER the scutum (front of thorax) OR T4+T5

6

5′

No white areas as described above

7

Bumbles showing White

 

6 (5′)

White scutum, golden abdomen

ID

6′

Scutum golden, T4 and T5 white

ID

Bumbles showing Yellow

 

7′

May have some yellow, but other colors also.  May be striped.

9

8#’

T4 mainly yellow

8

8 (7)

Abdominal T-1 thru T4 yellow, T5 and T6 black

ID

8′

Black wing band, T2 and T3 show some black

ID

Bumbles showing RED

 

9 (7′)

Bees showing RED on abdomen

10

9′

No red on abdomen

21

Separating Reds into 2 groups

 

10

RED on middle of abdomen

18

10′

RED at hind end of abdomen

18

“RED in middle of abdomen” group

 

11 (10)

Scutum yellow, T1 & T2 yellow, T3 & T4 red/orange, T5 black

ID

11′

Not as above

12

12 (11′)

Scutum cloudy, T1 & T2 yellow, T3 & T4 orange and/or black, T5 black

ID

Yellow head bumble bee, Bombus flavifrons, RED morph

12′

Not as above

13

13 (12′)

T2 & T3 red / orange

14

13′

T2 OR T3 show orange

17

14 (13)

Scutum cloudy

15

14′

Scutum yellow, no black hairs

16

15 (14)

Black inverted triangle on scutellum, range associated with San Juan Islands, often black notch on T2

ID

15′

T1 yellow, T4 black with white hairs in horizontal line

ID

16 (14′)

T4 yellow, range: drier, lower elevation, eastside lowlands

ID

16′

T4 yellow, high elevation specialist

ID

17 (13′)

Scutum and Scutellum both yellow, T2 usually shows at least some yellow, small body, very short face

ID

17′

Scutellum with black inverted triangle

ID

Red at hind end of abdomen

 

18 (10)

Scutum cloudy (yellow, with black hairs mixed in)

19

18′

Scutum yellow

20

19 (18)

T3 orange, sometimes with black; T4 & T5 orange; distinct red tail

ID

19′

T3 black, T4 & T5 pale orange hairs, can be subtle.

ID

No RED on Abdomen

 

21 (9)

 

No red, yes stripes

22

21′

Hind end of abdomen black

26

22

T1 & T4 white or yellow; inverted black triangle on scutellum

ID

22′

Not as above

23

23 (22′)

Face black, scutum and T4 yellow

ID

23′

Face yellow

24

24 (23′)

T3 all or partially yellow

ID

24′

T3 black

25

25 (24′)

Stergites black, hair length very even

ID

Bumbles with black end of abdomen

 

26 (21′)

Thorax & T1 thru T4 yellow, T5 black, corbiculum present

ID

26′

Not as above

27

27′

Not as above

28

28

T3 golden or yellow

29

28′

Not as above

30

29

Black dot between wings

ID

29′

No black dot between wings

ID

Morrison bumble bee, Bombus morrisoni (rare in WA, more common in OR and ID)

30 (28′)

Scutum cloudy, T1 & T2 yellow, possibly with black notches

ID

30′

Not as above

31

31 (30′)

T1 yellow, T2 with yellow or brown, relatively large bodied

ID

31′

T1 & T2 yellow, medium to small body size

ID

This is our start.   Version 1.1

If you find color morphs that fall outside this key, please bring them to our attention so we can expand the key appropriately.

Teamwork for the Win!

1

Washington's bumble bees

Bumble Bees of Washington State

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