There has been a flurry of excitement in the media over a recently-published observational study describing the “behavioural flexibility and adaptation” of solitary bees to our “plastic-rich environments”. In a nutshell, during the course of a larger field study looking at wild bees in urban landscapes, researchers in Toronto discovered that some urban Megachile bee species in the city had lined their nest cells with plastic materials.
Megachilid ‘leafcutter’ bees are solitary bee species that build their nests as rows of sealed cells inside natural cavities, like wood hollows or plant stems. To protect the developing larvae inside, the cells are lined with natural materials, like bits of leaves, flower petals, or plant resins.
So what do these bees do when they live in a city where the natural world is in short supply? Use the most available alternative material…ubiquitous plastics. The researchers found that one species (Megachile rotundata, the alfalfa leafcutter bee), which normally uses snippets of plant leaves to line their nests, had incorporated tiny pieces of plastic shopping bag into nest cells. The other species (Megachile campanulae), which normally collects resins from plants or trees to build the nest cell, had made do with a type of polyurethane-based sealant usually used to seal window frames.
Media coverage has been extensive, from science media to tabloid dailies, but the general theme appears to be the same: no need to feel bad about our impacts on the environment, animals are learning to cope just fine. Is this a “a rare piece of good news for bees“? Could it be optimistic evidence that bees are learning to adapt to a world increasingly dominated by humans, giving hope to the future of global food security?
Most newsy versions of the story focused on the study’s apparently remarkable finding that all the bee larvae in plastic-lined nests survived and were parasite-free. Apparently Plastic was no longer consorting with the Grim Reaper and had regained its crown as the patron of modern society…here was an ethical paracetamol for our collective headache of trying to live lightly in a consumerist world!
It’s true, plastic can prevent parasites from getting to bee larvae, as this USDA factsheet from 1970 discusses – nest cells constructed in plastic drinking straws will produce parasite-free bees, because the parasite cannot get through the plastic straw wall…but as we all know, plastic doesn’t breathe, and up to 90% of the larval brood can be lost to mould infestation in solid plastic nests, parasites or no parasites.
There is a bit more to the Toronto study that the newsy versions didn’t mention. Firstly, the urban bee nests did not have hermetically-sealed plastic linings – they were made up of mixed pieces of plastic and leaves. Therefore, their survival cannot be compared to survival inside solid plastic walls. Secondly, some of the bees emerging from the sealant-lined cells were parasitised by a generalist brood parasite, Monodontomerus obscurus. Thirdly, although the information in this observational study is important and useful, the sample size was too tiny to be considered evidence of any real effect.
The authors were simply reporting an ecological observation that occurred as part of a larger replicated study looking at other factors. In total, the number of trap nest cavities set out around Toronto for bees to settle into was 5700 (190 sets of 30 cardboard tubes). Out of 5700 possible nest cavities, this observational article is talking about 2 cavities, in which 5 individual brood cells were found to be plastic-lined. This is definitely not proof that wild bees can survive in plastic nest cells!
In their discussion, the researchers note the potential for plastic linings to stop parasites, but they also remind us that there are “many other examples of plastics inhibiting essential functions including mobility, foraging, and respiration in other animals”. Sadly, the newsy versions will be read more than the original article, and very few of these versions (briefly) acknowledge the other side of the story (e.g. here and here).
It is comforting to think that wildlife can adapt to changing environments, especially when we are responsible for that change. But we are already aware of the negative effects plastic exposure can have on foetal development, hormone function, skin health and even the results of scientific laboratory studies. Sometimes the effects aren’t seen immediately. What will we see in a few years, after multiple generations of bees have built and emerged from plastic-lined nests? Is this a cause for celebration that wildlife can survive human domination, or more incentive to start cutting the plastic umbilical cord?
© Manu Saunders 2014