Impact of Color and Size of Bowl Trap on Numbers of
Bees Captured
Sam Droege
Introduction
Through observations and field trials, creative bee researchers have discovered that plastic
salad bowls were fast, cheap and effective trapping systems for bees. In 200, the author ran
a number of trials comparing numbers of bees captured across a wide variety of both
ultraviolet (UV) and non-UV colors. The results indicated that yellow, blue, and white bowls
were indeed effective at capturing bees and that their UV counterparts could perhaps be even
more effective. In contrast bowls colored red, gray, clear, black, and green caught essentially
no bees. Those results will be written up elsewhere.
In this report I focus more intensely on 8 bowl colors: white, light blue, yellow, and blue and
their UV counterparts. Additionally I look at the effect of the size of the bowl to see if smaller
more efficient sizes could be used to replace the large 12 oz. bowls traditionally used.
I would like to thank the Coevolution Institute for their financial support and the aid of Harold
Ikerd, Betsy Jackson (who performed many of the size of bowl trials), Joann Alexander, Alex
Alfaro, Steve O’Brien, and Laura Hilden for their help in running trials, pinning, labeling, and
identifying bees and being of great help for little or no compensation. Frank Parker needs to
be mentioned here as the Godfather of the bee bowl and his encouragement directly led to
these studies. Thank you also to the Logan Bee Lab for their general encouragement,
inspiration, and willingness to answer many questions.
Methods
Bees were captured using bowls or cups filled with soapy water. Approximately 1-2
teaspoons of Dawn dishwashing liquid were added to a gallon jug of water and that mix
distributed to bowls in the field. Bowls were placed in transects on the ground 5m apart within
a uniform habitat. In the early spring habitats included forested ones, after the spring
wildflowers and blooming trees finished bowls were placed only in brushy or open areas.
Bowls were left out in the field for either 24 hours or set out prior to 9:30a.m. and picked up
after 3:00p.m. Each treatment in all trials was composed of 5 bowls or cups. Treatments
were alternated regularly within the transect. The bulk of the data were collected in Maryland
in between Baltimore and Washington, however, some trials were run in Texas, Colorado,
Maine, Pennsylvania, North Carolina, and Tennessee. The raw data can be seen in the
associated files: (Bowl Test Date Tables.xls). Data were collected from April until
September 2002.
Color Bowl Preference Study
12 oz. plastic Solo brand salad bowls were used. Solo colors for yellow, white, blue, and light
blue were chosen. As yet, spectral characteristics of these bowls have not been measured.
These colors matched generally match their descriptions with the exception of blue which
most people would describe as a dark blue. Matching ultraviolet (UV) colors for these colors
were created by spraying white Solo bowls with paint supplied by Nocturn Ultraviolet Visual
Effects (A unit of Xenotech-Strong International, North Hollywood, CA 91605). Thirty-seven
trials were run.
Size of Bowl Preference Study
The following plastic solo bowls and soufflé cups were used: 12 and 6 oz. bowls and 4, 3.25,
2, 1, 0.7 oz. soufflé cups. All were painted with yellow UV paint. Twenty-two trials were run.
Statistical Analyses
All analyses were performed using the Minitab statistical package.
Results
Color Bowls
A one-way ANOVA was used to investigate if the mean number of captures differed among
colors. As the tables below demonstrate, that indeed was found to be the case.
Analysis of Variance for Number of Bees
Source
DF
SS
MS
F
P
color
7
1846
264
2.32
0.026
Error
281
31979
114
Total
288
33825
Individual 95% CIs For Mean
Based on Pooled StDev
Level
N
Mean
StDev -------+---------+---------+--------blue
37
6.33
7.97
(--------*-------)
blue UV
35
12.51
18.06
(--------*--------)
pale b
36
8.48
7.31
(--------*--------)
pale bUV
36
10.95
10.61
(-------*--------)
white
37
8.06
8.45
(-------*--------)
white UV
36
7.69
8.00
(--------*--------)
yellow
35
5.03
6.09
(--------*-------)
yellow UV 37
12.13
13.66
(-------*--------)
-------+---------+---------+--------Pooled StDev =
10.67
4.0
8.0
12.0
Tukey's pairwise comparisons were performed to investigate which of these pairs of
colors differed significantly. Note that the UV colors (other than white UV, which,
interestingly, caught fewer bees than its non-UV counterpart) caught significantly
more bees than many of the non-UV colors. Also, in a bit of statistical irony, the
non-UV yellow had the lowest mean despite it being the bowl of choice in the old
days.
Family error rate = 0.0500
Individual error rate = 0.00264
Critical value = 4.29
Intervals for (column level mean) – (row level mean)
Significant Pairwise Differences are in Bold
blue
blue UV
pale blu
pale bUV
white
white UV
blue UV
-13.81
1.45
pale blu
-9.73
5.42
-3.66
11.71
pale bUV
-12.19
2.96
-6.12
9.24
-10.09
5.16
white
-9.25
5.80
-3.18
12.08
-7.15
8.00
-4.68
10.47
white UV
-8.94
6.21
-2.87
12.50
-6.84
8.42
-4.37
10.88
-7.21
7.94
yellow
-6.33
8.93
-0.26
15.21
-4.23
11.14
-1.76
13.60
-4.60
10.66
-5.02
10.34
-13.32
1.73
-7.25
8.01
-11.22
3.93
-8.75
6.40
-11.59
3.45
-12.01
3.14
yellow U
yellow
yellow U
-14.73
0.53
The figure below graphs the mean counts of bees captured in 5, 12 ounce plastic
bowls of the following colors: blue, UV blue, light blue, UV light blue, white, UV
white, yellow, UV yellow that were filled with soapy water for a day. There is
nothing new in this graph, really, but I think a bit clearer demonstration of the
differences and much easier to use in power point talks.
Because there were 20 trials from Maryland, and those were taken throughout the time of year
that bees were flying, a two-way ANOVA was used to investigate both the effect of color and
of date. Color slipped to a non-significance level in this test while date was found to be highly
significant. An inspection of the means for the different colors again shows high values for
Blue UV and Pale Blue UV but not for yellow UV.
Analysis of Variance for numbers of bees captured
Source
DF
SS
MS
F
P
datemd
17
8116.7
477.5
6.95
0.000
colormd
7
792.9
113.3
1.65
0.128
Error
119
8171.2
68.7
Total
143
17080.8
datemd
04/02/20
04/04/20
04/11/20
04/12/20
04/18/20
05/24/20
05/25/20
05/26/20
05/27/20
06/10/20
07/06/20
07/15/20
07/16/20
07/29/20
07/31/20
08/01/20
08/09/20
Mean
5.9
18.6
12.4
1.9
8.1
2.2
2.1
1.4
4.4
3.0
15.6
30.4
15.1
5.2
5.9
8.2
2.7
Individual 95% CI
-----+---------+---------+---------+-----(-----*-----)
(-----*----)
(----*-----)
(-----*-----)
(-----*-----)
(-----*-----)
(-----*-----)
(----*-----)
(----*-----)
(-----*-----)
(-----*----)
(----*-----)
(-----*-----)
(-----*-----)
(-----*-----)
(-----*-----)
(-----*----)
08/10/20
15.2
colormd
blue
blue UV
pale b
pale bUV
white
white UV
yellow
yellow UV
Mean
6.0
12.0
9.4
12.2
8.7
8.8
5.1
8.3
(-----*-----)
-----+---------+---------+---------+-----0.0
10.0
20.0
30.0
Individual 95% CI
-------+---------+---------+---------+---(---------*---------)
(---------*---------)
(--------*---------)
(---------*--------)
(---------*--------)
(---------*---------)
(---------*--------)
(---------*--------)
-------+---------+---------+---------+---4.0
8.0
12.0
16.0
Size of Bowl
The effect of size of bowl or cup was tested using a one-way ANOVA. The results are
below with the surprising result that no difference was found among the sizes. In
fact, the two smallest soufflé cups (about the size of spit cups) had the highest
means. If these results were standardized by the amount of water held in each cup
the differences would be quite dramatic.
Analysis of Variance for bees
Source
DF
SS
MS
size
6
192
32
Error
147
23602
161
Total
153
23794
Level
0.75
1.00
2.00
3.25
4.00
6.00
12.00
N
22
22
22
22
22
22
22
Pooled StDev =
Mean
8.97
10.97
7.46
7.68
8.23
7.77
8.77
12.67
StDev
13.36
18.94
10.26
12.45
9.98
8.29
12.58
F
0.20
P
0.977
Individual 95% CIs For Mean
Based on Pooled StDev
-----+---------+---------+---------+(------------*-------------)
(------------*-------------)
(-------------*------------)
(------------*-------------)
(-------------*------------)
(------------*-------------)
(------------*------------)
-----+---------+---------+---------+4.0
8.0
12.0
16.0
Again, a nice graph of the differences in means. Note the greatly truncated scale on the y-axis.
As with the colored bowls, a 2-way ANOVA was performed on Maryland data alone looking at
both size of bowls and date. Again, no significant difference among the sizes of bowls was
detected, however, date was significant.
Analysis of Variance for bees
Source
DF
SS
date
21
18105.4
size
6
192.0
Error
126
5497.0
Total
153
23794.5
date
03/28/20
03/29/20
04/2/200
04/3/200
04/30/20
05/8/200
05/9/200
05/24/20
07/3/200
07/11/20
08/11/20
08/13/20
08/15/20
08/17/20
08/23/20
08/25/20
09/5/200
09/12/20
Mean
5.4
6.7
6.5
28.6
43.9
7.6
1.0
7.7
30.7
9.4
5.7
6.7
4.4
1.6
0.9
5.7
3.2
0.7
MS
862.2
32.0
43.6
F
19.76
0.73
P
0.000
0.623
Individual 95% CI
---+---------+---------+---------+-------(---*--)
(--*---)
(--*---)
(--*--)
(--*---)
(--*--)
(---*--)
(--*--)
(--*---)
(--*---)
(--*--)
(--*---)
(--*--)
(--*--)
(---*--)
(--*--)
(--*--)
(--*---)
09/17/20
09/24/20
10/2/200
05/10/20
size
0.75
1.00
2.00
3.25
4.00
6.00
12.00
1.6
1.3
3.7
5.1
Mean
9.0
11.0
7.5
7.7
8.2
7.8
8.8
(--*--)
(--*--)
(--*---)
(--*---)
---+---------+---------+---------+-------0.0
15.0
30.0
45.0
Individual 95% CI
--+---------+---------+---------+--------(----------*----------)
(----------*----------)
(----------*----------)
(----------*----------)
(----------*----------)
(----------*----------)
(----------*----------)
--+---------+---------+---------+--------5.0
7.5
10.0
12.5
Discussion
The results presented here tantalize, but do not fulfill. There are clear indications that UVcolors significantly increase the catch of bees in bowl/cup traps. Additionally, as is true in so
many places, it is also clear that bigger is not necessarily better, at least in terms of number of
bees captured. In fact, if follow-up tests uphold these results, small bowls have the
advantages of using less water, being easy to carry and deploy with one hand, costing less,
taking up less volume in packs and luggage, being less conspicuous and tempting to curious
citizens, and using less paint.
However, both these results are incomplete in that we do not know the species composition of
the catch. It possibly could be the case that one of the colors with low bee numbers was
proficient in the capture of species not found in other colors. Species identifications are still
being determined and will be presented elsewhere.