250 B. Svensson et al. Agriculture, Ecosystems and Environment 77 2000 247–255
queens’ nest-seeking behaviour. This parasite ap- parently disturbs a queen’s orientation capacity. As
a result, infected queens search and dig in unusual places and continue nest-seeking until they die in the
later part of summer Lundberg and Svensson, 1975.
2.3. Statistical analysis To compare the activities of bumble bees in dif-
ferent landscape types and habitats, all results were transformed to total number of observations per 100 m
during the season
No. of observations 100 m
: No. of observations
mps ×
100 where mps metres per season for landscape types
= length of transect × number of inspections during
the period Table 1, and mps for habitat =length of each habitat in the total study area × number of
inspections during the period Table 1. The data were log transformed before the statisti-
cal analysis. One-factor ANOVA the SAS procedure GLM; SAS Institute Inc., 1982 was used to anal-
yse the data on landscape type n = 12 and habitat n = 96, respectively. To compare the landscape types
and habitats pairwise, a PDIFF command was used.
To analyse the data on bumble bee species, a split-plot design was used the SAS procedure GLM;
SAS Institute Inc., 1982, with the bumble bee species as the dependent variable. The independent variables
were landscape type quadrats as error term and habitat n = 96.
3. Results and discussion
Some 147 observations of nest-seeking bumble bee queens Bombus spp. were recorded in this study and
the following species were observed: Bombus lucorum L., Bombus terrestris L., Bombus pratorum L., Bom-
bus pascuorum Scop., Bombus lapidarius L., Bom- bus sylvarum L., Bombus subterraneus L. and Bombus
hortorum L. B. lucorum accounted for 76 of the ob- servations 52, whereas B. pratorum and B. horto-
rum were recorded only once and thrice, respectively Table 2.
Bumble bees all observations showed significant preferences for certain landscape types p 0.05,
Table 2 Bumble bee Bombus spp. species observed searching for nesting
sites in an agricultural landscape near Uppsala during April–June 1991
Species Abbr.
a
Number
b
Obs.
c
N.Q.
d
B. lucorum LU
76 52 13 April
13 April B. terrestris
TE 18 12
14 April 14 April
B. pratorum PR
1 1 25 April
13 May B. pascuorum
PA 10 7
7 May 7 May
B. lapidarius LA
14 9 11 May
24 May B. sylvarum
SY 10 7
11 May 29 May
B. subterranius SU
15 10 26 May
29 May B. hortorum
HO 3 2
29 May 7 June
Total 147
a
Abbreviations for species names.
b
Number of individuals observed during the period; and per- centage of total numbers observed within parentheses.
c
Date of first observation obs..
d
Date of the first observed nest-seeking queen of each species.
n = 12. There were more observations of bumble bees in RO than in the other landscape types Fig. 1.
In pairwise comparisons, differences between RO and RW and between RO and W were statistically signif-
icant p 0.05, n = 12 and the difference between RO and O was almost so p = 0.051, n = 12. The
number of species observed was also highest in RO.
One reason for these high values in the relatively open landscape could be that this type of landscape had
the greatest habitat diversity seven out of eight habi- tats were represented, Table 1. Richards 1978 found
that Canadian bumble bee species differed in their nesting-site preferences and ascribed these differences
to niche specialisation. Other authors have also re- ported differences in habitat Skovgaard, 1936; Fussell
and Corbet, 1992b and altitudinal zone Svensson and Lundberg, 1977 preferences among bumble bee
species.
When landscape types with the same number of habitats were compared, more nest-seeking queens
were found in the open landscape than in the rela- tively wooded one. In addition, the open landscape
had a relatively high species diversity five species, even though there were only four habitats present.
Thus, habitat diversity is apparently not the only factor affecting the number of bumble bee species nesting
in a given landscape type.
Few studies have been made with the aim of com- paring the occurrence of bumble bees in different
landscape types. The present study showed statisti-
B. Svensson et al. Agriculture, Ecosystems and Environment 77 2000 247–255 251
Fig. 1. Number of nest-seeking bumble bees observed per 100 m transect in different landscape types. Abbreviations for landscape types and species defined in Tables 1 and 2, respectively.
Table 3 Result of pairwise comparisons
a
between numbers of nest-seeking bumble bee queens observed in seven different habitats
b
F Fb
P Op
C Rb
Fob F
n.s. n.s.
n.s. Fb
n.s. n.s.
n.s. n.s.
P n.s.
n.s. n.s.
Op n.s.
n.s. C
n.s. Rb
Fob
a
p 0.05; p 0.01; n.s., no significant difference.
b
Habitat abbreviations defined in Table 1.
cal differences among the landscape types and the results are consistent with Skovgaard’s 1936 find-
ings in agricultural landscapes in Denmark, which showed that nest-selecting queens are influenced by
the landscapes’ character and vegetation, and that species-specific preferences exist.
Bumble bees’ preference for the habitats differed significantly p 0.01, n = 96 8 habitats × 12 tran-
sects. Nest-seeking queens were observed most fre- quently in Fob Fig. 2, and they were also frequently
encountered in Op and Fb. The frequency of encoun- ters was somewhat higher in Rb, than in F and P. The
frequency of nest-seeking queens was low in C, and none was observed in Fo. Table 3 shows significant
differences among habitats in pairwise comparisons. The highest occurrence of queens in forest bound-
aries probably reflects a preference for sites offering some degree of shelter. In their survey in England
where the public participated in reporting observa- tions of bumble bee nest sites, Fussell and Corbet
1992b found that most nests were sheltered from wind. However, the high score for forest boundaries
could also be ascribed to the strong preference of B. lucorum queens for this type of habitat. When this
species was excluded from the analysis, the habitat ‘other open ground’ ranked highest in terms of fre-
quency.
The habitat with the highest number of species of bumble bees was road boundary five species were ob-
served nest-seeking in this habitat type, although the density of observations total per 100 m of investigated
transect was lower than in forest boundary and field boundary types. The number of observations in pas-
ture varied between transects. Most observations were made in pastures with only a few grazing animals and
with an abundance of grass.
In the field habitat, nest-seeking queens were ob- served only in grass ley, which is less disturbed
than other crops; one reason being that, normally, no ploughing is carried out for at least three consecutive
years. No nest-seeking bumble bees were observed in fields with annual crops. These results add statistical
value to earlier findings Skovgaard, 1936; Fussell
252 B. Svensson et al. Agriculture, Ecosystems and Environment 77 2000 247–255
Fig. 2. Number of nest-seeking bumble bees observed per 100 m transect in different habitats. Abbreviations for habitat and species defined in Tables 1 and 2, respectively.
and Corbet, 1992b, showing that uncultivated areas are of greater value as nesting places, compared with
cultivated areas. Fig. 3 shows characteristics of the patches where
bumble bee queens were searching for nesting places. Withered grass and tussocks are typically found in un-
cultivated areas. Almost all bumble bees of all species showed searching behaviour in patches with withered
grass 92, and most of them searched where the oc- currence of withered grass was considerable. In addi-
tion, 86 of the queens were observed in patches with tussocks, and 70 of the bumble bees were observed
in patches where new grass was uncommon or absent. Of the observations, 31 were made in patches where
stones were frequent, and 35 were made in stoneless patches. Only 24 of the queens showed nest-seeking
behaviour in patches with moss.
Queens of the latest emerging species were ob- served nest-seeking on patches with new grass more
frequently than queens of the earlier emerging species. This difference is probably the result of higher abun-
dance of new grass later in the season, when the late-appearing queens are most active.
Skovgaard 1936 concluded that the association be- tween bumble bee nests and stony ground is not as
strong as some studies indicate. In the present study, one third of the observed queens were nest-seeking
in patches without stones, which accords with Skov- gaard’s 1936 observations. The frequency and place-
ment of underground bumble bee nests are probably dependent on the abundance of abandoned rodents’
nests Svensson and Lundberg, 1977; Harder, 1986. Only eight of the 14 species of bumble bees men-
tioned by Løken 1973 as occurring in this part of Sweden were recorded in this study. In studies car-
ried out in recent years in Norway Dramstad and Fry, 1995; Saville et al., 1997 and Great Britain Fussell
and Corbet, 1991, only seven and six species, respec- tively, were found in landscapes of similar, or greater,
size than in the present investigation. In eastern Fin- land, Ranta and Tiainen 1982 found ten species and
Skovgaard 1936 mentioned 13 species in his report from Denmark. Pekkarinen 1984 found that numbers
of species in European areas were similar throughout the continent. The lower numbers recorded in recent
investigations may reflect a decline in species diver- sity, as has been reported from England Williams,
1982.
The eight bumble bee species Bombus spp. ob- served in this study, have been divided into those that
prefer open terrain i.e., B. terrestris, B. lapidarius, B. sylvarum and B. subterraneus and those that pre-
fer forest boundaries i.e., B. lucorum and B. pascuo- rum. This grouping is in agreement with earlier inves-
tigations Skovgaard, 1936; Ranta and Tiainen, 1982; Reinig, 1972. However, no firm conclusions concern-
ing B. pratorum or B. hortorum can be drawn because of the restricted numbers of observations.
B. Svensson et al. Agriculture, Ecosystems and Environment 77 2000 247–255 253
Fig. 3. Characteristics of patches within all habitats where nest-seeking activities were observed as a percentage of total number of observations for each set of patch characteristics n = 147. Occurrence of characteristics within patches is classified as absent, low, medium
or high WG, withered grass; NG, new grass; TU, tussocks; ST, stone; and MO, moss.
B. lucorum was the earliest emerging and most gen- eralistic species. This conflicts with the assertion by
Richards 1978 that early species tend to be special- ists. In the present study, this species was observed in
all landscape types Fig. 1 and habitats, except for- est Fig. 2. The densities in different habitats were
significantly different p 0.05, n = 96. It was most abundant in forest boundaries. During the course of
the study period, it became the most frequent species as well. Of this species, 80 were observed in patches
with stones and they tended to search where stones were frequent Fig. 4. The only patch characteristic
that was associated with few observations of B. lu- corum, was new grass, probably because the queens
were nest-seeking so early in the season. Therefore, it is concluded that although queens of B. lucorum can
be found searching for nesting sites in almost all areas in the agricultural landscape, they seem to prefer for-
est boundaries in the relatively open landscape with lots of withered grass, tussocks and stones.
The difficulty in discerning between workers of B. lucorum and B. terrestris, because of their similar
colour patterns, has led to them being treated as a sin- gle species in some studies e.g., Fussell and Corbet,
1991; Dramstad and Fry, 1995; Saville et al., 1997. However, morphological differences are more distinct
between queens of the two species. Thus, the present study was able to document differences in their choice
of habitat for nesting places. B. terrestris was observed only in field boundaries
and other open ground Fig. 2, and the frequency with which it was encountered differed significantly
among the habitats p 0.01, n = 96. The first queens also appeared very early in the season Table 2. This
species, in particular, tended to be observed in patches where there was little new grass, whereas all species
that appeared later in the season ,searched for nests predominantly in patches with new grass, i.e., at least
90 of the observations for each species Fig. 4. B. terrestris was strongly associated with withered grass
and seemed to prefer field boundaries and other open ground in various types of agricultural landscape with
much withered grass and tussocks. It was often found searching in patches lacking most of the characteristics
included in our analysis.
In contrast, B. pascuorum searched for nesting sites in diverse types of patches. This species preferred
patches with stones 80, and it was often found where the frequency of stones was low or medium
Fig. 4. Of the B. pascuorum queens observed, 60 were in patches with moss. All observed queens of
this species were found on forest boundaries Fig. 2. This habitat differed significantly from all others as re-
gards the distribution of this species p 0.05, n = 96.
254 B. Svensson et al. Agriculture, Ecosystems and Environment 77 2000 247–255
Fig. 4. Patch characteristics for the six most frequent bumble bee species within all habitats where nest-seeking activities were observed. The result is shown as the percentage of the total number of observations for each species and for each set of patch characteristics.
Occurrence of characteristics within patches is classified as absent, low, medium or high WG, withered grass; NG, new grass; TU, tussocks; ST, stone; and MO, moss.
In northern Sweden, Svensson and Lundberg 1977 found that this species seemed to prefer open areas
with tussocks. It seems probable that bumble bees in southern Sweden prefer locations sheltered from wind
and sun, whereas queens in northern Sweden prefer open areas, in order to get more warmth from di-
rect sunlight. The present findings agree with those of Skovgaard 1936, who found that B. pascuorum is,
despite its trivial name ‘field bumble bee’, associated with woodland, where it builds its nest in moss.
B. lapidarius was found only in open and relatively open landscapes Fig. 1, where it searched for nest-
ing places in many different habitats Fig. 2. Of the queens observed of this species, 57 were in patches
with stones, but the frequency of stones in these patches was generally low Fig. 4. B. lapidarius did
B. Svensson et al. Agriculture, Ecosystems and Environment 77 2000 247–255 255
not appear to be keenly interested in tussocks or stones, despite this species sometimes being called the ‘stone
bumble bee’. This agrees with Skovgaard 1936, who found this species to be associated with grassy areas
and to have generalistic habitat preference.
Almost all B. sylvarum observed were found in rela- tively open landscape Fig. 1, and this difference was
statistically significant when comparing species dis- tributions among landscape types p 0.05, n = 96.
Skovgaard 1936 also observed that B. sylvarum, de- spite its species name, is not found in forest, a fact
borne out by the present study.
Queens of B. subterraneus also preferred open type landscape, as found by Reinig 1972. They were
found only in open and relatively open landscapes Fig. 1. This species was observed in other open
ground, road boundaries and field boundaries Fig. 2, and the frequencies with which it was observed
differed significantly among the habitats p 0.01, n = 96. B. subterraneus was the only species that
was never observed in mossy patches. It was also uncommon in stony patches.
4. Conclusion
