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What to look for this week - Bumblebees

Published: 06 May 2020

The glorious sunny weather we were treated to last week was also enjoyed by some other Shetland residents, notably bumblebees. There were certainly plenty buzzing around my garden and probably yours too – most of mine were feeding on willow catkins, the pollen providing a welcome food source until a few more herbs start to flower and provide nectar. Pollen is rich in protein, nectar rich in sugar.  

All of these bumblebees will be queens. Only mated female (queen) bumblebees survive over winter, buried a few centimetres down in the soil. They emerge once the sun has warmed the soil enough to awaken them from hibernation. After feeding up they are soon on the look-out for a new nest site – typically a whole in the ground or occasionally a shed roof.

Once she has decided on her nest she collects pollen and stores it in the nest chamber. Look closely and you can see the baskets on her hind legs in which she transports the pollen. Queens can carry up to 75% of their body weight in pollen; imagine bringing back nine stones of shopping from your next visit to the supermarket! She then makes a wax cell on the pollen store and lays her first brood of eggs. After five days of brooding the larvae hatch. They feed on the pollen and nectar which she brings and after two or three weeks each spins a cocoon and pupates. Two weeks later a bumblebee emerges. All of these, however, are female workers. Their job in life is simply to go and forage for nectar and pollen to help the queen raise more broods of eggs. No sex for them!

At some point when the colony is mature the queen lays her last brood of eggs. Some of these develop into males and females (young queens). This signals the beginning of the end for the colony. The males usually develop first, leave the nest and patrol regular routes along which they place scent hoping to attract a young queen from another colony for mating. Each species has its own particular scent. Once mated the young queen builds up enough body fat to survive the winter and then finds a location to hibernate. Their body can produce glycerol, a form of anti-freeze, should the temperature dip to low. Queens are easily told from workers as they are much larger – almost twice the size.

Bumblebees are fascinating creatures.  To fly, their muscles which are located in the thorax, must be around 30 to 40 degrees centigrade. They warm up by shivering, sitting in the sun or taking advantage of a warm surface. Flying keeps them warm, their wings flap an incredible 200 times a second(!) but this requires a lot of energy. Think of it this way. If we run it takes us around half an hour to consume the calories in one Mars Bar but a human-sized bumblebee would consume the same number of calories in less than 30 seconds! Their ability to fly in cool temperatures at either end of the day gives them a big advantage over other insects as they can continue feeding for longer.

Bumblebee populations have crashed over much of mainland Britain, where modern, intensive agriculture leaves little room for flowers. Fortunately they are faring better here in Shetland where agriculture is less intensive and there has been a boom in gardening. Bumblebees are incredibly important pollinators of flowers, including commercial crops such as tomatoes, peas, apples and several berries.

Until recently Shetland was home to four species of bumblebee but in the last few years two more species have colonised the islands – a product of global warming perhaps. They can be difficult to identify but we have a few tips.  You can also find out more in our new Bumblebees leaflet.

First up is it a Shetland Bumblebee. These are pretty obvious as they look very different with an orange thorax (upper body) and yellow abdomen (lower body). The recent colonist the Early Bumblebee is also distinctive as they have a yellow and black stripe on both the thorax and abdomen but the give-away is the orange tip to the abdomen - giving them an orange-tailed look. Then it gets tricky so look at the thorax (upper body). This will have either a yellow - black - yellow i.e. triple banding (Garden and Heath), or simply a yellow - black i.e. double banding (Northern White-tailed or Buff-tailed). If its a Garden or Heath then you really have to get close enough to see the shape of the face – short and round in Heath, or long and thin in Garden, not of the feint-hearted! if its a Northern White-tailed or Buff-tailed then look at the tail (the bottom bit of the lower body or abdomen). If this is pure snow white then it will be a Northern White-tailed but if it has a hint of buffy yellow (sometimes actually quite a deep orangey yellow) then it will be a Buff-tailed.

Shetland Amenity Trust is keen to receive records of bumblebees so that we can get a better picture of their abundance and distribution in the islands. So if you do see and can identify a bumblebee why not e-mail us at paul.harvey@shetlandamenity.org . A photo will help us confirm the identification.

Photo: A Shetland bumblebee, our most distinctive species with its burnt orange thorax (upper  body) and contrasting yellow abdomen (lower body). This one is feeding on Bird’s-foot Trefoil has lost a few of its yellow hairs so the black of the body is showing through.  

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