[This article is a work in progress]
I am increasingly convinced that bumblebee markings are primarily a device for camouflage (or crypsis) as the scientists like to call it, rather than a warning device (warning mimicry). The paper referenced at the bottom of this article is one of the few I have been able to find that make reference to other theories and research into the reasons for bumblebee markings, some dating back as early as the 1920's.
The paper makes the point that actually very little research has been done in this area and that the mainly held view has been that bee markings are a warning device to predators. When a predator gets a nasty sting they associate the bright colours/markins with the displeasure and learn to avoid the colours in future. However, one of the few UK studies to examine this theory actually found no such benefit.
The author tentatively suggests the possibility of camouflage as a benefit almost as an aside. We had already begun to come to this conclusion from our own observations and photographic record of bees in captivity and this has subquenently been demonstrated further with bees in the wild.
Our sample is small and our observations are visual rather than statistical - none-the-less, we feel able to present some additional evidence for the theory that bumblebees are coloured primarily for camouflage in the wild. We should also consider the concept of Dazzle Camouflage.
The capture and subsequent care of Holly, our little disabled bee, has allowed us a degree of close study that perhaps would not easily be afforded under normal circumstances. Holly cannot fly, so she can be studied in either "lab" or "natural" conditions as we choose, because she does not have the freedom to escape.
Because she cannot successfully forage in the wild we have kept her in a semi-enclosed private habitat, with elements of her natural environment as well as man made elements. This allows us to see which habitats she naturally favours as well as how she behaves within them. Over the days we have begun to see patterns in her behaviour that we can report here.
We don't necessarily have explanations for these patterns, but we can certainly suggest some. The most striking things we have noticed is about her incredible colour match and camouflage in respect of the moss in the tub, as well as her outright preference to choose this as her resting habitat. The two factors may be related.
Three weeks after taking care of Holly we found another bee with identical disability and we introduced this bee to the same controlled environment as Holly. After 24 hours of uncertainty, they now cohabit successfully.
What can and can't be explained
We are aware that in order to demonstrate our camouflage theory with scientific rigour we would have to conduct robust trials that show statistical evidence that bees of certain colours are better protected from predators in certain environments. This would be no mean feat to achieve, in terms of number of bees required for statistical evidence and the ability to track them in the wild, even for a team of dedicated researchers. As two hobbyists with a scientific interest, this is simply not possible for us. Our evidence is therefore emipircal and anecdotal, but at least (we hope) well informed.
Firstly, we are very concious that we have primarily studied Bufftail bumblebees (Bombus Terrestris) and that a general theory of camouflage would have to explain the difference in markings for each Bombus species. Perhaps the hardest to explain are the species with red tails: Redtailed (Lapidarius), Early (Pratorum) and Blaeberry (Monticola) bumblebees; intuitively their colouring would seem to offer less protection.
In contrast, however, most of these species have slight variations in preferred nesting location and in some cases (e.g. Tree Bumblebee Bombus Hypnorum) there is an obvious visual synergy between the colour of the bee and the its natural nesting environment.
We are also conscious of Mans' contirbution to the changing environment for bees - the sheds, decking, rockeries, country gardens and artificial environments that man (perhaps inadvertently) provides for bees to nest, are a relatively recent addition to the environment bees would naturally choose; so we have been keen to see what bees actually do "out in the wild" as well as under controlled conditions. If anything, it is this that has cemented our belief in the hypothesis.
The first two of these images were taken within moments of each other about a metre apart in a deep ditch at the edge of the nearby field. Both bumbleebees appeared to be resting and preening in the Sun on a warm sunny afternoon. One was most definitely a Garden Bumblebee queen, of which I obtained some remarkable macro shots. Neither of these bees was up for moving nor initimidated by my presence, despite getting the camera to within a few inches. At a first glance they are pretty hard to spot - but it is interesting that each has chosen a location within the vicinity of each other, best suited to their individual colourings.
This next photo was taken after the summer when our sunflowers bloomed late. They were regularly visited by Common Carder bees and we noticed that this was where they chose to stay when they were spending time resting in the sun. Again, the colour match against the surroudings, and even the way the colour is organised and broken up is immediately apparent.
Full set on Flickr:
We found Holly on the ground within 2.5 day of our box being installed. We can't be sure how well developed our colony was by that stage, but it would have been fairly new with only a few bees - especially judging by the sound (or lack of) coming from it and compared to how it is now it is well-developed. Ultimately Holly was a recent addition to the colony and would not have had a long time exposed to other members of the colony or indeed to the outside world at all, including predators and plants.
- It's been interesting, therefore, to see the following behaviours develop and change over time as we have kept her in her tub:
- choosing moss over other materials as the place to rest, shelter and keep warm
- increasingly defending herself when we take the lid off her box with increasing levels of warning, even though (or because) no harm ever comes to her
- adopting face-first position into the moss when resting - exposing both her sting and camouflage bands when vulnerable
- gradual reduction in "perimeter survey" behaviour and appparent attempts to find a way out of the box
- general reduction in exploratory behaviour, save for new items introduced to the box; she will explore the item then return to her safe haven, then explore a little more, then return several times over
- circling on the spot or in a small area (we have no explanation for this) - sometimes tugging a little at the paper towel floor she is on
- finding the warmest spot in the tub to rest and warm up
This paper is an interesting analysis of the distribution of bee colour patterns across the world and it is not conclusive in terms of understanding the purpose; indeed, some aspects are counter intuitive (for example, the colours required for thermoregulation appear to group in the opposite way expected).
The author anecdotally suggests some basis for camouflage, but this is not measured. He also references some early papers which mentioned camouflage, but again did not study it.