Many species of bumblebee have black and yellow stripes, an obvious warning sign in nature to predators that hunt by sight. Only females, i.e. queens and workers, have a poisonous sting as well. You would think bumblebees would have a safe life with few enemies. Nothing is further from the truth! During the various stages of their lives, they are ‘attacked’ by many organisms:
Predators: organisms that kill and consume many prey items during their lifetime; e.g. cheetah
Parasites: an organism that depends upon another organism for its life support system by living inside its host or on the surface; e.g. head lice. Some parasites may even effect the behaviour of its host to benefit the parasite.
Parasitoids: specialist organisms that develop within or on its host, usually ending in the gruesome death of the host; e.g. encarsia formosa, the tiny wasp used by organic gardeners to control aphids or for those of you more interested in science fiction and have seen the film ‘Alien’, will know what is meant!
Kleptoparasites: when one organism takes or steals the food or nest material of another organism, e.g. I have watched a blackbird whilst it watched a thrush as it smashed a snail’s shell and then stole the snail! Or have you ever had your chips stolen by a passing seagull? !
Safe inside the nest?
Bumblebees are social insects and as such live in a communal nest. A relatively small, but densely packed permanent food store, with a mobile population, themselves a potential food source. A treasure store for some opportunists. Here inside the nest, with a guards or two at the entrance, you would think they would be safe. Not so. When a queen initiates the start of the colony she has to find a suitable nest site, tend and care for her eggs or offspring, build and defend the nest and her offspring. Whilst she is out foraging invaders such as ants, centipedes, earwigs, or mice, may undertake a sneak theft of her eggs or grubs or eat them there. She may come under attack and killed by a cuckoo bumblebee, who will then enslave the previous queen’s workers to tend her own offspring.
Once the nest is well established, with numerous workers and guards you think they would be safe then. Again, not so! The nest contains living larvae, eggs, perhaps dead adults, wax, pollen, nectar and other food items all in one place ready for the taking, providing the taker is crafty! And crafty they are!
A few moths lay their eggs inside, in particular, the wax moth (Aphomia sociella) is a major pest and is said to be one of the bumblebees’ most serious enemy, particularly in urban areas, where the bumblebee’s nests may be easier to find. It sneaks in under cover of darkness to hide and lay her eggs with devastating effect. Although Sladen may never have found wax moth larvae in nests of B. Lapidarius, these wax moth larvae had obviously not red his book!
Then there’s a flesh fly called Brachicoma devia which enters bumblebees nests and lay their living larvae on the skins of the unsuspecting bumblebee larvae. These larvae, do n’t want a small bumblebee larvae to feed upon, they want a larger one to sustain them for their life own change. So they wait for their ‘meals’ to be fed and tended by their sister worker bees. When the bumblebee larvae are well fed and start to pupate and spin a cocoon, the Brachicoma devia larvae start their feast. Many scavengers will live inside the nest feeding on the waste material inside nests. The common house fly larvae will be found feasting away and even some species of hover fly toss their eggs into the nest entrance hole and if they are lucky will fly away to live again. If killed by the workers, they go into automatic ‘egg laying’ mode and carry on laying eggs even when dead! Their larvae feed upon the detritus inside the nest. I have also found snails inside nests that have been subject to infestations of wax moth larvae. Various small beetles and their larvae may also scavenge a living from the nest.
There is a large hoverfly called Volucella bombylans, which instead of mimicking a hoverfly, this strongly resembles some species of bumblebees, even down to a furry coat! It too lays its eggs inside bumblebee nests where the larvae eat through the detritus and possibly eat bumblebee larvae too.
Safe when flying?
The bumblebees are out foraging and flying to and fro. Are they safe as they fly? Not a chance! The larger robber flies will catch flying prey and ambush them mid flight, particularly the larger species. Some bumblebees may fall victim to spiders caught in their webs, something I have myself seen. Some fall victim to motor vehicles, when after colliding with them, we quickly buzz off on our way!
What catches them when they land?
Probably caught by a great tit, which after pecking out the stings goes on to eat the juicy insides!The crab spider is a specialist ambusher. It conceal itself under or on flower petals and has the ability to mimic the colour of the flower, a perfect and deadly camouflage.see how they capture bumblebees here on this BBC video…… http://bbc.in/fHhJ9q
Conopid flies also wait at flowers and as a bumblebee lands on the flower, the conopid launches itself onto the back of the bumblebee and expertly inserts a single egg inside the bumblebee’s body, with her razor sharp ovipositor. Soon the egg hatches and consumes the bumblebee from the inside, eventually killing the bee, whose corpse then becomes the flies coffin inside of which it spends the winter months, to emerge next summer.
I actually saw a species of conopid called Sicus ferrugineus, see here… http://bit.ly/kjMPaG
as it displayed typical egg laying activity. It waited actually on a B. terrestris nest box I have at home, a few inches from the entrance to the nest. As son as an unfortunate bumblebee left the nest, it launched straight after it like a flash. The fly zooms in, banks alongside, expertly deposits its eggs inside and immediately returned back to its ‘perch’. Waiting and the same happened when the next bumblebee left the nest. I saw this action 20 times and decided enough was enough and chased it away from ‘my’ nest!
The now UK established bee-wolf, ( Philanthus triangulum) includes honey bees in its diet and may well attack smaller bumblebees. Hornets are also assassins of bumblebees.
Larger predators could include, badgers, foxes, weasels, moles, shrews, voles, mink, field mice, dormice, blue tits, spotted flycatchers, hedgehogs, Sladen mentions swallows and we now have video evidence of crows, grey squirrels, great tits and mice predating on bumblebees actually at their nest sites….
see BBC video…… http://bbc.in/dGWnAM
Then there are mites, who hitch hike a ride on bumblebees, using flowers as staging posts and some can even be choosey about which ride they will hitched to, preferring some species and rejecting others,( there are even mites that hitch a ride on these mites!!). Some mites live in the nest, some are blood sucking mites and smaller still are the microscopic enemies such as Nosema bombi, which lives in bumblebee larvae and adults intestines, various bacterias, fungal pathogens. nematode worms and viruses.
Safe in hibernation?
The young queens have safely passed through the dangerous times some of their sisters and brothers have had to endure and after mating finds a suitable hibernation site. Even here is not safe. A nematode, Sphaerularia bombi, live and mate in the soil. Fertilised females invade the hibernating queens as they sleep, possibly through the mouth. Some species of mites also hibernate on the queen’s body, ready to invade her nest, others live inside her, awaiting spring when they feast on her blood and later infect the queens workers.
Read more articles about the bumblebee nest box and ways incorporated into nest box to deter pests
For more information and to help save bumblebees join the Bumblebee Conservation Trust.
Refs with my own experiences, observations and thanks to Steve McWilliam from Cheshire’s LRC...
|Benton,T. (2006). “Bumblebees”Harper Collins Publisher, London.|
Goulson, D. ( 2010). “Bumblebees behaviour, ecology and conservation” Oxford University press, Oxford.
Prys-Jones, O E. & Corbet S A. (1987). “Bumblebees” University of Cambridge
Sladen, F. (1912). “The humble-bee. Its life history and how to domesticate it” Macmillian and Co. Ltd, London