Above - Bumblebee foraging on Phacelia
Bumblebee foraging behaviours are complex, with many
When do bumblebees visit flowers for food, and why do they choose particular flowers? How far will bumblebees fly to find food and do they ‘tell their friends’ when they’ve found a rewarding flower patch?
Here we explore some of these questions.
Honey bees famously perform a ‘waggle dance’ – a figure of 8 dance on vertical honey combs to indicate the location of food sources to other honey bee workers in the colony.
The honey bee waggle dance was famously decoded by Karl von Frisch 1967, who won a Nobel Prize for his work.
More recently, it has been suggested that the honey bee dance language may also be influenced by the environment in which the honey bees are foraging (Chittka 2009).
It is believed that bumblebees do not perform a waggle dance to communicate food locations as such. However, returning foragers run around the nest emitting a pheromone which is believed to stimulate foraging behaviour (Dornhaus and Chittka 1999, 2001).
Interestingly, stingless bees appear to perform a kind of dance which some may find reminiscent of the honey bee waggle dance, although again, it is not clear whether the dance itself confirms the location of appropriate flora (Chittka 2009).
Do bumblebees prefer to forage alone, or are they happy to forage with other bumblebees and how do they know which flowers to visit?
Some evidence suggests that bumblebees may learn about rewarding flower species (i.e. species of flowers which provide lots of nectar and pollen), directly through observing other conspecific foragers (i.e. bees of the same species) (Worden and Papaj 2005).
Bumblebees will also switch flower species to a more rewarding alternative more quickly if other bees are foraging there than if alone, because they are attracted to occupied flowers (Leadbeater and Chittka 2007).
……But Foraging Efficiently…
However, despite a willingness to forage together, bees are able to detect and avoid visiting flowers which have recently been visited by other bees. How?
Bees have an oily residue on the whole surface of their bodies, including the feet. Research has suggested that upon visiting flowers, at least some species leave a trace of this residue behind.
Honey bees, for example, use these temporary scent marks act as a repellent in order that other honey bees can distinguish and reject flowers that have recently been visited by themselves or their colony members. This means they avoid wasting time by exploring and probing empty flowers.
It has been found that bumblebee species also exhibit this behaviour. The bumblebee species Bombus terrestris and Bombus pascuorum were able to distinguish and avoid flowers which had previously been visited by conspecifics and other Bombus species. (Goulson, Hawson and Stout 1998).
Nectar robbing describes the taking of nectar from flowers without entering the flower (and thus without pollinating it). Bumblebees achieve this by biting the base of the flower to get accces to the nectar (see the photograph right). Bumblebees (usually short-tongued bumblebees) are believed to be more likely to engage in this behaviour.
(When insects feed from a hole in the flower created by nectar robbing, this is called secondary robbing).
How far do bumblebees fly for food?
Flight and foraging ranges are variable, dependent on species and environmental factors (i.e. availability of rewarding flowers).
In honey bees, recorded foraging distance has ranged from 1-6fm, but (rarely) up to 20km, whilst
Solitary bee species are thought to fly only a few hundred metres (Shcwartz and Hurst 1997) - although a distance of 25km has been recorded for euglossine bees (Janzen 1971).
However, the data on bumblebees does not provide a clear picture, to my knowledge. Various studies have been carried out, but the results are rather mixed and not conclusive. In some instances, the results could be said to have been a product of the study design, rather than providing a realistic picture of bumblebee foraging distances. However, there is some evidence suggesting that foraging ranges vary according to the different bumblebee species (i.e. some forage closer to the nest, others further away) and it is also possible that there is some correlation between foraging range and nest (colony) size, with bumblebee species from typically smaller colonies tending to forage closer to home (less than 1500m) than those with larger colony size - i.e. more than 2 km from the nest (Walther-Hellwig and Frankl 2000).
You can read more about how far bees fly, with links to scientific papers on this page.
Manufacturers of pesticides (including garden insecticides) may advise their application during the morning, to minimise the risk to bees, which may be foraging.
However, a study by Herrera (1990) showed that in two common garden species studied (Bombus terrestris and Bombus lucorum), foraging activity peaked early (5am – 7am) and late (5 – 7 pm). Note that ‘peak’ nevertheless can imply that some foraging may also occur outside of those times.
Bumblebees are famously hardy, and can withstand cold temperatures due to their ability to vibrate their bodies and generate terrific heat. This is exactly what the bumblebee queen must do when she emerges from hibernation. Bumblebees have even been photographed foraging on the flowers of mahonia, peeping through snow. However, not surprisingly, rain is poor weather for bumblebees.
It is believed that bees learn to favour flowers that have previously provided a reward, thus they continue to forage on the species whilst ever the reward remains available.
This makes for efficient foraging, since the complex shapes of some flowers means that bees may have to develop the knack of gaining access to the pollen and nectar stores within.
Once the bee has learned how to efficiently tackle a flower species, it therefore makes sense to exploit it for food whilst the nourishment remains available.
Flowers attract their perfect pollinators in various ways. They have developed characteristics (pollination syndromes) such as scent (sweet scented flowers are preferred by bumblebees) and visual cues, such as the ultra violet patterns on petals which guide bees onto a ‘landing platform’.
Flower shapes also play a role in that some flower species are visited only by particular bees. For instance Hypericum vouytcheuse are visited for pollen only by Bombus lucorum and Bombus pascuorum workers using buzz foraging.
It is well known that different bumblebee species have different tongue lengths. Whilst it seems this could affect the foraging behaviour of bumblebees, it should be noted that even within a single colony, tongue length can vary, simply because of the varied sizes of the workers and males.
Read about nectar robbing.
Find out more about bumblebees
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