Asian long-horned beetle [photo: Kyle Ramirez]

Invasive Species: Stowaways in the Supply Chain

The supply chain you operate may be delivering more than you bargained for, if the goods or materials you ship are accompanied by pests that have hitched a ride.

Despite your best efforts to operate a low-carbon, ethical business, people won’t remember you fondly if you introduce an invasive species. In simple terms, that’s a plant or animal that isn’t native to a particular place, and that subsequently thrives. The consequences for native plants and wildlife can be devastating, threatening local biodiversity, harming local industry and providing a huge headache for the people who try to clean up the outbreak.

Thankfully, we’re a bit less naïve about this issue nowadays. It’s still possible to buy some exotic plants or pets, have them escape from your garden and multiply halfway across the country, but the dangers are at least recognised. Since April 1st 2014 you can no longer buy floating pennywort (or four other plants) in an English garden centre – although you can probably find plenty of the stuff choking a nearby canal or lake.

Floating pennywort

Floating pennywort

Modern biosecurity policies represent quite a change from the mid-nineteenth century, when European settlers formed ‘Acclimatisation Societies’ to make the colonies seem more familiar. They introduced plants to make their gardens feel more like home, and they introduced animals too; in order to hunt them for food, for economic reasons, or just to make the landscape ‘look right’… and they didn’t understand the damage that the introduction of a few rabbits would do to Australia – nor that of taking possums from Australia and introducing them to New Zealand.

Truckload of dead possums

Cruel, or necessary? It’s a question of perspective. Disposing of possums in New Zealand, where they carry bovine tuberculosis and pose a terrible threat to biodiversity.

All too often, the results are catastrophic. Invasive species thrive when they find themselves in a place where their traditional predators don’t exist, and where the new things they choose to eat have no defence against them. Competition between species is nothing new of course: everything that still exists has a long, long history of competing for space, for sunlight, for food and so on, but the modern-day pace of change is a hundred times faster than when the distribution of organisms was based upon mechanisms such as coconuts falling in the ocean and being washed up on strange shores. With international trade comes the international distribution of invasive species.

As I mentioned back in August, an awful lot of wood gets used for packaging materials such as pallets. According to Wax [2014] making pallets and the like in the USA accounts for a staggering 44% of US hardwood production. That’s bad enough in itself, but a pallet also offers in-transit accommodation and catering for certain burrowing insects.

The emerald ash borer (agrilus planipennis) is native to Asia and Eastern Russia, but in June 2002 they were found in Michigan, USA, having arrived in shipping materials. Once in North America they multiplied rapidly, finding that the local ash trees had little resistance and there were no predators or parasites to threaten them. It is expected that the emerald ash borer will ultimately kill most American ash trees – a process that takes about ten years, but is too rapid to allow the ash to produce seedlings before it succumbs. The cost of fighting the infestation (not winning, just fighting) is estimated by Kovacs et al [2010] to be $10.7 billion over a ten-year period.

Pallets should be treated before being moved across a national boundary, either with heat (130° F for half an hour) or with methyl bromide – a highly toxic substance that attacks the ozone layer as well. Only its importance in biosecurity has kept it from being phased out… but one can’t help feeling that (as so often in the sustainability field) we’re trying to solve one problem by introducing another.

“I know an old lady who swallowed a fly…”

It’s not just pallets that pick up hitchhikers, though: any ship that takes on ballast water, in order to manage its stability, and subsequently discharges that water elsewhere may have given a free ride to a vast quantity of plants, animals, viruses or bacteria.

When zebra mussels showed up in the Great Lakes (USA / Canada) in 1988, it was clear these fingernail-sized natives of the Caspian Sea hadn’t got there of their own accord: they’d either been transported in ballast water, or (less likely) attached themselves to an anchor or chain. The total cost of the zebra mussel invasion, to date, is estimated at $5 billion.

Zebra mussels

Zebra mussels attach themselves to any hard surface, causing considerable damage to vessels and pipes… as well as edging out native species.

The International Maritime Organization has done a lot to slow the transfer of invasive species via ballast water, but acknowledges that the problem may not have peaked yet: the incidence of outbreaks continues to increase with the growth in seaborne trade. Their list of the “ten most unwanted” makes depressing reading.

I first became alerted to ballast water as a vector during my study of the cruise industry, but if you think about it, a cruise ship is probably going to discharge less ballast water than a cargo ship, because its all-up weight isn’t going to vary all that much from one port of call to the next. Nonetheless, Klein [2008] reports that noncompliance with ballast water regulations in California led to Carnival Cruise Lines paying a $200,000 administrative fee to settle with the California State Lands Commission.

For everybody involved, it seems that biosecurity is a lot cheaper when you get it right first time.



Klein, R.A. (2008) ‘Cruise Ship Squeeze: The New Pirates of the Seven Seas’, Gabriola Island: New Society Publishers

Kovacs, K.F., Haight, R.G., McCullough D.G., Mercader, R.J., Siegert, N.W. and Liebhold, A.M. (2010) ‘Cost of potential emerald ash borer damage in U.S. communities, 2009–2019’, Ecological Economics 69, 569–578 [available online]

Wax, J. (2014) ‘99 Percent Invisible: Wooden Pallets Carry Environmental Costs Along with Their Loads’ Earth Island Journal, January 10th, 2014 [available online]


One thought on “Invasive Species: Stowaways in the Supply Chain

  1. Great post. This is an issue very relevant to Australia. I didn’t know about the possums in NZ. I’m pleased to hear that compliance with ballast water regs are being enforced. Green tree frogs often stow away in crates of bananas & are flown back to Qld.

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