A plastic new world

By Athayde Tonhasca

Mr McGuire: I want to say one word to you. Just one word.

Benjamin: Yes, sir.

Mr McGuire: Are you listening?

Benjamin: Yes, I am.

Mr McGuire: Plastics.

Film buffs will recognise one the most quoted dialogues in motion picture history, where Mr McGuire advises young Benjamin Braddock on his career options in the 1967 classic ‘The Graduate’.

Mr McGuire was prescient: the plastics industry has expanded to levels unimaginable in 1967. Cheap, versatile, resistant and durable, plastic products are essential in today’s society. They are everywhere. So, unsurprisingly, they are an ever growing environmental problem: land, waterways and the oceans are stuffed with discarded plastic. 

Plastic rubbish is a blight on the landscape, but some birds and mammals have taken advantage of this abundance of material. Squirrels and opossums have learned to use straws, string and plastic bags for nest building; plastic fragments were present in about 14% of surveyed nests of the brown booby (Sula leucogaster), a seabird found around the world. So, diligent nest builders such as leaf-cutter bees were bound to join this team of opportunists.

Most leaf-cutter bees (genus Megachile) cut pieces of leaves or petals to build their nests; some use mud, pebbles or resin as construction materials. These bees usually nest in sheltered natural cavities such as burrows, crevices and hollow twigs. They are important pollinators, and a few species have been reared commercially for crop production, such as the alfalfa leaf-cutter bee (Megachile rotundata).

Top: A Megachile centuncularis at work. This is one of seven megachilid bees in Britain. Bottom: A leaf-cutter bee nest © Line Sabroe (top) and Subbu Subramanya, Wikipedia Creative Commons

In Ontario, Canada, alfalfa leaf-cutter bees have been creative and resourceful by using pieces of polyethylene-based shopping bags as a building material. Another local species, the bellflower resin bee (Megachile campanulae), constructs nests with plant resins instead of pieces of plants. It has no use for plastic bags, but polyurethane-based sealants, which are applied to the exteriors of buildings, offer a handy and abundant alternative. Some bellflower resin bees mixed this plastic product with natural resins to build their nests.

Brood cells partially constructed with polyethylene plastic bag fragments (L,) and polyethylene resin © MacIvor & Moore 2013, Ecosphere 4(12) art155

Rural areas are not exempt from the plastic deluge. In the Argentinian countryside, bits of greenhouse covers, agrochemical containers, fertilizer bags and irrigation hoses combine with ubiquitous shopping bags to deface the landscape. One bee, possibly an alfalfa leaf-cutter bee, took advantage of this clutter to do away with leaves or petals completely: she built an entire nest with pieces of two types of plastic.

Plastic brood cells (L) and pieces of plastic used in the construction of a leaf-cutter nest © Allasino et al. 2019, Apidologie 50: 230-233

We don’t know whether plastics have any effect on leaf-cutter bees. They may be neutral, or even beneficial; plastics may act as a barrier against fungi and parasites, which are important mortality factors for solitary bees. On the other hand, these impermeable materials may trap water and thus increase the brood’s susceptibility to diseases. 

By using plastics, bees have demonstrated their ability to identify alternative and convenient resources, and to adjust to changes in their environment. All the same, plastic nests are another troubling sign of a world living in the Anthropocene. From the Greek anthropos (man) and cene (new or recent), this unofficially labelled geological epoch applies to Earth’s history since humans started to have a significant impact on climate and ecosystems. It’s a new world of mass extinctions, deforestation, pollution, fossil fuels, and climate change. Perhaps leaf-cutter bees can adapt and even flourish in this world. We may do the same. Or not.