Bee Stings (Part Two): What you need to know about bumblebees

Bumblebee stings

Many of you reading this may be fearful of the loud, fuzzy bumblebees that busily fly about during Spring and Summer months. And your fear may well be justified. Bumblebees sting. And unlike honeybees, they do not die when they sting you. Their stinger, a smooth needle with no barbed edges, can easily pierce exoskeletons and skin alike… repeatedly. ^1,2

Bumblebee’s needle-like stinger. Image source: Anna’s Bee World

Just like other bees and wasps, the bumblebee’s stinger is modified from a piece of egg-laying apparatus called an ovipositor.¹ Therefore, only female bumblebees can sting, and instead use a small pore on their abdomen to lay eggs.¹ Males are completely harmless.

Why do bumblebees sting?

Simply put, bumblebees only sting when their life or their colony is at risk. However, it takes a lot to anger these gentle giants of the bee world.²

While the sting of a bumblebee usually causes humans minor injuries, it can be much more serious for smaller predators, sometimes even killing them.³ You would think very few creatures would be reckless enough to choose a bumblebee for their lunch, however, animals such as badgers, shrews, birds, hornets, dragonflies and some large spiders are all known to predate on bumblebees.⁴

Badgers target the bumblebee colonies, eating almost everything in sight from the small amounts of honey to grubs, their claws making easy work of digging up and ripping apart a bumblebee comb. ⁶ Although I am not really sure how they can cope with a colony of angry bees, I imagine their thick skin and nocturnal habits give them a serious advantage. ⁷

A bumblebee stinging a shrew in the nose.⁵

Crab spider with its bumblebee prey. Image source: Alex Hyde Photography

Bee-eater ready to snack on a bumblebee. Image source: Birds of Russia (Photographer: Vladimir Ezhov)

Birds can be a little craftier when it comes to eating bumblebees, often removing the stinger of a bumblebee before getting stuck in. In fact, birds like the specialist bee-eaters rub or hit the abdomen of the bee along a branch or hard surface, causing the bee to release its venom or lose its sting completely.⁸ Watch here to see a clever bee-eater in action.

With predators left, right and centre, it pays to be able to defend yourself and your colony. Even better is to be avoided completely, which is why many bees have the classic black and yellow warning colouring signalling to predators that they are not worth the trouble. This is shared by many stinging insects (Müllerian mimicry) as it means predators don’t have to learn many different warning signals. Some non-stinging insects cheat and have similar colouration to bluff to predators that they can also do them harm (Batesian mimicry).^{9, 10} In one study, toads that learned to avoid bumblebee prey also avoided the bumblebee-mimicking robber-fly. ¹¹

The American bumblebee (left) and its stingless mimic, a robber fly (right). Image source: Discover Life, Bug Guide.

Workers in a colony can sniff out any intruders entering their colony.¹² Larger colonies of buff- and white-tailed bumblebee appoint guard bees who examine incoming bees.¹³ They can smell differences between their own sisters and workers of the same species from other colonies. Any strangers entering the colony will be quickly greeted with an onslaught of stings and bites.¹²

A guard buff-tailed bumblebee on duty in a commercial bumblebee colony. Image source: Nik Sargent Observations

Some bumblebees can be feistier than others, even within the same colony. One study found that bumblebees more active in defending their colony had higher ovarian indices (number of potential egg cells in ovarioles) than those less active. Some species, such as buff- and white-tailed bumblebees, are known to be generally more aggressive than those like the early bumblebee (B. pratorum).¹²

However, sometimes bumblebees use their stings for entirely more selfish purposes. This is the case with cuckoo bumblebees. Cuckoo bumblebees belong to the subgenus Psithyrus and are thought to be evolutionary descended from the ‘true’ bumblebees (subgenus Bombus).¹⁴

Cuckoo bumblebee checking out a bumblebee colony in a man-made nest. Image source: Nurturing Nature

Cuckoo bumblebees do not build their own nests. Instead, much like cuckoo birds, they sniff out and take over established colonies of the hardworking social bumblebees.^1,2,14 This is no easy task; the cuckoo bee must sneak past the guard of workers and usurp the reigning queen. She may do this with a disguise; cuckoo species tend to have similar patterns to the species they parasitise.¹⁵

Bombus vestalis, a cuckoo bee, has no pollen baskets on its hind legs and morphologically resembles ‘true’ bumblebee species such as the buff- and white-tailed bumblebee. Image source: Entomology Today (Photographer: Stephen Falk).

Timing is also essential; striking too late will mean that a colony is too large and strong to let any intruder pass. ^1,2,15 By invading the colony before the second batch of workers have emerged, she has a good chance at success.² She engages the queen of the colony in a fight to the death and the odds to win are certainly not equal. Cuckoo bee females have thicker armour, and an even longer stinger.² The cuckoo bee injects the soon-to-be-defeated queen with her stinger, filling her with venom enough to kill her. The cuckoo bee lays her own eggs, and the late queen’s daughters raise them.

Bumblebee venom & allergic reactions

As serendipity would have it, during the time I was writing this blog, I was stung by a bumblebee for the first time. I was transferring the bee to a tube and suddenly felt a needle prick in the tip of my finger, followed by throbbing pain where the sting had occurred and then a low pulsing ache in my hand. After taking an antihistamine, this passed within a half hour or so. Merissa, PhD student in AP lab studying effects of pesticides on bumblebees (see her blogs here) had a stronger reaction to a bumblebee sting in her finger, experiencing “shivers” up her arms throughout the entire day following the sting.

An unfortunate dachshund on the receiving end of a bumblebee sting. Couldn’t resist including this. Image source: Metro

When a bumblebee stings, it injects a cocktail of molecules known as venom (as opposed to poison, a substance that is toxic if ingested or absorbed) into its target. Their venom includes small molecules like sugars and amino acids, peptides and proteins.¹⁷ 72% of the molecules in bumblebee venom found by one study were identified as homologs to honeybee venom proteins, which indicates similar function and heritage of these proteins in both bees.¹⁶ However, bumblebees have only about half as many compounds in their venom than the honeybees do.  Furthermore, some bumblebees have venom that is only half as toxic as honeybee venom.

This may be because bumblebees don’t sting vertebrates as often as honeybees do. They also only have their nest for a season, whereas honeybees keep their hives through the winter and over a couple of years, meaning the greater the need to defend it.¹⁶

Diagram depicting the majority of the human population’s response to a bumblebee sting. Image soure: Koppert Biological Systems

People (and other animals, like dogs¹⁸) often have varying degrees of reactions to bee stings, from just a short-lived, localised pain like I experienced to much more severe allergic reactions. But why do some people have allergies to bee stings and others don’t?

An allergy is basically an overreaction of the immune system towards certain molecules that are normally harmless. Antibodies are produced in response to these molecules and cause a biochemical, chain reaction, known as an allergic reaction.¹⁹

Sometimes an allergy to one type of bee sting can cause someone to be allergic to other types of bees that they have never been stung by – this is called a cross-reaction.¹⁶ As bumblebee and honeybee venom share many venom components & proteins, despite being separated by 100 million years of evolution²⁰, it is quite common for people who have honeybee allergies to also be allergic to bumblebee stings.²¹ People with allergies only to bumblebee-specific compounds will likely not have severe reactions to honeybee stings, and this has implications for how people with different bee sting allergies are treated medically.²²

Although allergies to bumblebee stings are rare¹⁷, there have been increases in bumblebee stings and allergic reactions to these stings among people working with imported bumblebee colonies used to pollinate crops like strawberries.²³

What to do if you are stung

Stay calm. As most people only experience short-term pain and minor swelling, an antihistamine should be enough to reduce or prevent worse symptoms within an hour or so.

Monitor resulting symptoms. If you experience any digestive issues, difficulties in breathing, heart palpitations or fainting then get to a doctor ASAP.²⁴

2 simple ways to avoid being stung

• Don’t be conspicuous. If working in close contact with bees, don’t wear perfumes or strong-smelling products, as these can attract or annoy bees. They are also sensitive to scents such as perspiration and alcohol. They also take a dislike to some jewellery and watches due to the smell of oxidised metal.
  
• Leave the bees be. Don’t swat or hit them away, don’t pick them up or touch them and definitely don’t go poking around or disturbing their colonies. If you leave them be, they’ll pass you no heed and continue on their way providing their important pollination services

References

1. Alford, D. V. (1978). The life of the bumblebee. Northern Bee Books, Hebden Bridge.
2. Goulson, D. (2003). Bumblebees: their behaviour and ecology. Oxford University Press, USA.
3. De Graaf, D. C., Aerts, M., Danneels, E., & Devreese, B. (2009). Bee, wasp and ant venomics pave the way for a component-resolved diagnosis of sting allergy. Journal of Proteomics, 72(2), 145-154.
4. Comont, R. (2017). RSPB Spotlight Bumblebees. Bloomsbury Natural History, UK.
5. Van Dyck, S. (2005). Bumblebees. Lerner Publications, USA.  
6. Goulson, D., O’Connor, S., & Park, K. J. (2018). Causes of colony mortality in bumblebees. Animal conservation, 21(1), 45-53.
7. The Wildlife Trusts (2019). European Badger. The Wildlife Trusts. [Retrieved 29 July 2019, from https://bit.ly/2YputtG].
8. Fry, C. H. (1983) ‘Honeybee predation by bee-eaters, with economic considerations’, Bee World, 64(2), 65-78.
9. Barnard, C. J. (2004). Animal behaviour: Mechanism, development, function and evolution. Pearson Education, Harlow.
10. Heinrich, B. (2004). Bumblebee economics. Harvard University Press, USA.
11. Brower, L. P., Brower, J. V. Z., & Westcott, P. W. (1960). Experimental studies of mimicry. 5. The reactions of toads (Bufo terrestris) to bumblebees (Bombus americanorum) and their robberfly mimics (Mallophora bomboides), with a discussion of aggressive mimicry. The American Naturalist, 94(878), 343-355.
12. Free, J. B. (1958). The defence of bumblebee colonies. Behaviour, 12(3), 233-242.
13. Sargent, N. (2019). Bumblebee Observations. [Retrieved 29 July 2019, from https://bit.ly/2LPcniO]
14. Cameron, S. A., Hines, H. M., & Williams, P. H. (2007). A comprehensive phylogeny of the bumble bees (Bombus). Biological Journal of the Linnean Society, 91(1), 161-188.
15. Williams, P. H. (2008). Do the parasitic Psithyrus resemble their host bumblebees in colour pattern? Apidologie, 39(6), 637-649.
16. Van Vaerenbergh, M., Debyser, G., Smagghe, G., Devreese, B., & de Graaf, D. C. (2015). Unraveling the venom proteome of the bumblebee (Bombus terrestris) by integrating a combinatorial peptide ligand library approach with FT-ICR MS. Toxicon, 102, 81-88.
17. Bucher, C., Korner, P., & Wüthrich, B. (2001). Allergy to bumblebee venom. Current opinion in allergy and clinical immunology, 1(4), 361-365.
18. Thomas, E., Mandell, D. C., & Waddell, L. S. (2013). Survival after anaphylaxis induced by a bumblebee sting in a dog. Journal of the American Animal Hospital Association, 49(3), 210-215.
19. Annila, I. (2000). Bee venom allergy. Clinical & Experimental Allergy, 30(12), 1682-1687.
20. Stolle, E., Wilfert, L., Schmid-Hempel, R., Schmid-Hempel, P., Kube, M., Reinhardt, R., Moritz, R.F.A., 2011. A second generation genetic map of the bumblebee Bombus terrestris (Linnaeus, 1758) reveals slow genome and chromosome evolution in the Apidae. BMC Genomics, 12(48).
21. Cruz, S., Vega, A., Fernandez, S., Marques, L., Baltasar, M., Alonso, A., Jorro, G., Moreno, A., Sánchez-Morillas, L., Miranda, A., Soriano, V., Fernández, J. & Guspi, R.;  (2012). Report from the Hymenoptera Committee of the Spanish Society of Allergology and Clinical Immunology: immunotherapy with bumblebee venom. Journal of investigational allergology & clinical immunology, 22(5), 377.
22. Hoffman, D. R., El-Choufani, S. E., Smith, M. M., & de Groot, H. (2001). Occupational allergy to bumblebees: Allergens of Bombus terrestris. Journal of allergy and clinical immunology, 108(5), 855-860.
23. Josef, P. (1993). Occupational allergy to bumble bee venom. Clinical Experimental Allergy, 23(10), 878–878. doi:10.1111/j.1365-2222.1993.tb00268.x 
24. Koppert Biological Systems. Treatment of bumblebee stings and allergies. Koppert Biological Systems. [Retrieved 29 July 2019, from https://bit.ly/2Y6wijI]

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