Open access journal: http://periodicos.uefs.br/index.php/sociobiology
ISSN: 0361-6525

DOI: 10.13102/sociobiology.v69i2.5459Sociobiology 69(2): e5459 (June, 2022)

The behavior of forming sleeping aggregations on 
stems of bushes and trees or in the nesting site to sleep at night 
is characteristic of many species of bees and wasps (Evans & 
Linsley, 1960; Linsley, 1962; Alves-dos-Santos et al., 2002). 
Records of these insects forming sleeping aggregations 
have been made for more than a century, but there is no full 
understanding of the reasons for this phenomenon (Banks, 
1902; Bradley, 1908; Rau & Rau, 1916). However, studies 
suggest that such behavior may be related to thermoregulation 
(Evans & Gillaspy, 1964; Linsley & Cazier, 1972), defense 
against predation (Evans & Linsley, 1960; Alcock, 1998) or 
the evolution of social behavior (Grassé, 1942). 

Bees’ sleeping aggregations are usually composed of 
males because females usually spend the nights inside their 
nests (Alcock, 1998). Sleeping aggregations can last weeks, 
months (Evans & Linsley, 1960) or even years when shared by 
individuals of different generations (Linsley, 1962). Sleeping 
aggregations of male in the tribe Eucerini (Apidae) have 
already been reported for different species (Table 1). Here 
we describe the general aspects of the behavior of Melissodes 

Abstract  
Bee males are sometimes found forming sleeping aggregations on stems of 
bushes or trees to sleep at night, but there is no complete understanding 
of the reasons for this behaviour. This note describes the behavior of 
Melissodes (Ecplectica) nigroaenea (Smith, 1854) males forming temporary 
sleeping aggregations in dry inflorescences of Bidens pilosa L. The sleeping 
aggregations of M. nigroaenea were observed for approximately 15 days in 
an area of Cerrado, Brasília, DF. During the day M. nigroaenea males visit 
flowers of Cosmos sulphureus Cav. near the sleeping aggregations, where the 
females collect pollen. In the late afternoon, the males return to the sleeping 
aggregations, where they sleep at night. These data provide new information 
about the behavior of M. nigroaenea males.

Sociobiology
An international journal on social insects

Wagner P. Silva, Rogério R. Andrade

Article History

Edited by
Evandro Nascimento Silva, UEFS, Brazil
Received                            16 December 2021
Initial acceptance             19 March 2022
Final acceptance               11 June 2022
Publication date                24 June 2022

Keywords 
Bees, dormitory, night shelter, solitary bees.

Corresponding author 
Wagner Pereira Silva 
Laboratório de Hymenoptera, Instituto de 
Biologia, Universidade de Brasília  
70910-900, Brasília, DF, Brazil 
E-Mail: wagner.sillva@yahoo.com.br

(Ecplectica) nigroaenea (Smith, 1854) males in two sleeping 
aggregation in Central Brazil.

Two sleeping aggregations of M. nigroaenea males 
were established for  approximately 15 days, between March 
and April 2018, and observed (about 30 h) in an agroforest 
on the campus Darcy Ribeiro of the University of Brasília 
(UnB), Federal District, Brazil (15°45’51.1” S, 47°52’05.4” 
W), where native plant species are maintained and cultivated 
in a soil rich in exogenous organic matter and green manure. 
Two species of Asteraceae – Bidens pilosa L. and Cosmos 
sulphureus Cav. – stand out in the place by the occurrence 
of several species of bees such as Bombus (Fervidobombus) 
pauloensis Friese, 1913; Epanthidium tigrinum (Schrottky, 
1905); Megachile spp. Latreille, 1802 using the reproductive 
structures of the plants to sleep. The sleeping aggregations of 
M. nigroaenea were recorded in inflorescences of B. pilosa, 
at about 40 and 60 cm above the ground, and approximately 
15 cm between both. The highest number of males was 
recorded in March when five and ten males, respectively, 
in the 40 and 60 cm sleeping aggregations were recorded. 

Laboratório de Hymenoptera, Instituto de Biologia, Universidade de Brasília, Brasilia-DF, Brazil

Male Sleeping Aggregation of Melissodes (Ecplectica) nigroaenea (Smith, 1854) (Hymenoptera, 
Apidae, Eucerini) in Brazilian Cerrado

ID

SHoRT NoTE

mailto:wagner.sillva@yahoo.com.br
https://orcid.org/0000-0002-5199-3124


Running title: Wagner P. Silva, Rogério R. Andrade – Male Sleeping Aggregation of Melissodes (Ecplectica) nigroaenea2

The collected specimens (n = 2) were assembled, identified 
and deposited in the Entomological Collection of UnB 
(Department of Zoology).

The first males arrived at the sleeping aggregation 
site around 16:00 h (Figure 1). M. nigroaenea males used 
the mandibles to fix themselves to the dry inflorescences of 
B. pilosa. This way of attaching to the substrate has been 
observed in many bee species, f. ex. Coelioxys deplanata 
Cresson, 1878; Melissoptila aff. bonaerensis Holmberg, 1903; 

Centris (Paracentris) xanthomelaena Moure & Castro, 2001 
(Linsley, 1962; Mahlmann et al., 2014; Martins et al., 2018). 
After clinging to the inflorescences, the males used fore 
and middle legs to find the ideal position to establish in the 
sleeping aggregation and spend the night (Figure 2). Some 
males then frictioned the hind legs, concomitantly, sometimes 
scrubbing them against the sterna or terga. This behavior of 
scrubbing the legs and the sterna or terga may be related to 
chemical signaling, being observed also in Tetrapedia species 
(Alves-dos-Santos et al., 2009).

Fig 1. Male sleeping aggregation on dried inflorescence of Bidens pilosa 60 cm above the ground (A) Melissodes nigroaenea 
males arriving at the sleeping aggregation. (B) M. nigroaenea males trying to find a position in the sleeping aggregation.

Interactions between the M. nigroaenea males were 
registered in some situations, usually due to the arrival of a 
new individual at the sleeping aggregation, which collided 
with another male, establishing for a few seconds some contact. 
These interactions almost always occurred when the last males 
arrived at the sleeping aggregations, around 17:00 h, and 
other individuals were already resting. Males left the sleeping 
aggregations early in the morning, resting individuals were not 
observed after 07:00 h. However, on two or three occasions 
M. nigroaenea males were recorded returning to their sleeping 
places and during the day when it was cloudy or raining.

Females of M. nigroaenea were observed (about 
30 individuals) collecting pollen, mainly between 10:00 
and 16:00 h, in flowers of C. sulphureus near the sleeping 
aggregations. M. nigroaenea males (n = 4) were often observed 
ingesting nectar from the flowers of C. sulphureus, but 
of copulations on flowers were not observed (Figure 3). 

Fig 2. Melissodes nigroaenea males fixed in Bidens pilosa through 
the mandibles at the sleeping aggregation 40 cm above the ground.



Sociobiology 69(2): e5459 (June, 2022) 3

According to Chemsak & Thorp (1962), Melissodes robustior 
Cockerell, 1915 males seem to present a preference for 
sleeping in Cosmos sp. flowers, where females collect pollen. 
Some authors suggest that establishing sleeping aggregations 
near flowers used by females as a source of floral resources 
may represent a strategy adopted by males in the search 
for mates on the next days (Alves-dos-Santos et al., 2009; 
Pinheiro et al., 2017).

Mahlmann et al. (2014) also recorded a sleeping 
aggregation formed by M. nigroaenea males. The individuals 
of two Eucerini species – M. nigroaenea and Melissoptila 
aff. bonaerensis – formed an sleeping aggregation where 
the individuals remained fixed through the mandibles in dry 
inflorescences of Hyptis sp. (Lamiaceae). Other studies report 
sleeping aggregations formed by individuals of both sexes 
(Evans & Linsley, 1960; Starr & Vélez, 2009; Yokoi et al., 

Fig 3. Male of Melissodes nigroaenea ingesting nectar in flower of Cosmos sulphureus.

Table 1. Sleeping aggregations records of Eucerini available in the literature.

Species Substrates Sex Reference

Florilegus (Florilegus) condignus Cresson 1878 On racemes of Medicago sativa (Fabaceae) Male LaBerge & Ribble (1966)

Gaesochira obscura (Smith, 1879) Stems of an unidentified species Unknown Rau & Rau (1916)

Melissodes (Ecplectica) nigroaenea (Smith, 1854)
Dried inflorescence of Hyptis sp. (Lamiaceae)
Dried stems of Bidens pilosa L. (Asteraceae)

Male
Male

Mahlmann et al. (2014)
Present study

Melissodes (Eumelissodes) agilis Cress 1878
Stems of an unidentified species
In sunflowers (Helianthus sp., Asteraceae)

Unknown
Unknown

Bradley (1908)
Rau & Rau (1916)

Melissodes (Eumelissodes) denticulata Smith, 1854 Verbena stricta (Verbenaceae) Male Mathewson & Daly (1955)

Melissodes (Eumelissodes) robustior Cockerell, 1915 Inside flower of Cosmos sp. (Asteraceae) Male Chemsak & Thorp (1962)

Melissodes (Eumelissodes) vernoniae Robertson, 1902 Verbena stricta (Verbenaceae) Male Mathewson & Daly (1955)

Melissodes (Melissodes) bimaculata (Lepeletier, 1825)
Stems of an unidentified species
Stems of an unidentified species
Melilotus sp. (Fabaceae)

Unknown
Unknown
Unknown

Banks (1902)
Rau & Rau (1916)
Rau (1938)

Melissodes verroniana Robt. Stems of an unidentified species Unknown Rau & Rau (1916)

Melissoptila aff. bonaerensis Holmberg, 1903 Dried inflorescence of Hyptis sp. (Lamiaceae)
Males, 
females

Mahlmann et al. (2014)

Svastra (Brachymelissodes) cressonii (Dalla Torre, 1896) Petioles of leaves of unidentified species Male Cockerell (1915)

Svastra (Epimelissodes) obliqua (Say, 1837) Stems of unidentified species Male Rau & Rau (1916)

Svastra (Idiomelissodes) duplocincta (Cockerell, 1905)

Leaf or stem of Encelia farinosa (Asteraceae)
Leaf or stem of Calliandra eriophylla (Fabaceae)
Leaf or stem of Ruellia peninsulares (Acanthaceae)
Leaf or stem of Justicia californica (Acanthaceae)

Male
Male
Male
Male

Alcock (1998)
Alcock (1998)
Alcock (1998)
Alcock (1998)



Running title: Wagner P. Silva, Rogério R. Andrade – Male Sleeping Aggregation of Melissodes (Ecplectica) nigroaenea4

2016, 2017). However, in the present study only M. nigroaenea 
males were observed in both sleeping aggregations.

Many explanations of the functions of aggregations 
have been proposed, but are still inconclusive. Sleeping 
aggregations could represent a strategy to reduce the risk 
of nocturnal predation, although it could also represent a 
greater risk of predation as has already been described for 
stingless bees (Evans & Linsley, 1960; Brown, 1997; Alcock, 
1998). Another benefit that sleeping aggregations could 
provide would be the possibility of elevating the capacity of 
individuals to thermoregulate, since in the face of a possible 
predator, the bees could present a minimum ideal temperature 
to perform the flight activity and consequently escape (Linsley 
& Cazier, 1972). The hypothesis that males form sleeping 
aggregations near sources of pollen visited by possible 
reproductive partners cannot be discarded. Thus, Cosmos 
flowers could serve not only as a source of floral resource but 
also as a mating site for Eucerini species (Chemsak & Thorp, 
1962). Besides sleeping in aggregations, some studies have 
reported Eucerini males sleeping inside flowers mainly from 
Cucurbitaceae and Orchidaceae (Hurd & Linsley, 1964; Dafni 
et al., 1981; Willis & Kevan, 1995; Vereecken et al., 2012; 
Watts et al., 2013).

There is not yet full understanding of the factors 
that determine the establishment of sleeping aggregations. 
However, our observations add new information about the 
behavior of Eucerini males. Future studies, addressing how 
this behavior may be related to a possible strategy of defense 
or sexual selection in solitary bees are needed.

Acknowledgements

The authors thank Dr. Antonio J.C. Aguiar (Department 
of Zoology/UnB) and Dr. João Bernardo de Azevedo Bringel 
Júnior (Department of Botany/UnB), respectively, for the 
identification of the bees and plant species. WP Silva thanks 
the Coordenação de Aperfeiçoamento de Pessoal de Nível 
Superior (CAPES), under Finance Code 001, for granting 
a doctoral fellowship. RR Andrade thanks the Fundação de 
Apoio à Pesquisa do Distrito Federal (FAPDF) for granting a 
undergraduate scholarship.

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