International plant trade is spreading invasive species and pests

Continental European snakes, geckos, and Italian wall lizards are silently making their way to northern Europe. They travel undetected among ornamental plants such as olive trees that are imported for gardens and green spaces.

These hidden plant hitchhikers can become invasive species, threatening native ecosystems – just as they have in snake-free Mediterranean islands like Majorca.

Importing ornamental plants

The presence of these reptiles signals a larger problem. Ornamental plants and cut flowers transport a wide range of pests, including insects, fungi, and disease-carrying organisms. These shipments move at high speed and in large volumes, making thorough inspections nearly impossible.

A study published in the journal Bioscience warns that despite regulations, imported plants pose an increasing risk. The global market for ornamental plants is expanding rapidly, and stronger regulations are urgently needed to prevent environmental and agricultural damage.

“Ornamental olive trees for sale in the UK can be over 100 years old, with many hiding places amongst their gnarly bark and the soil they’re transported in. This is incredibly risky in terms of importing pests,” said Professor William Sutherland from the University of Cambridge.

“Adult snakes and lizards are just the tip of the iceberg. If they’re getting through, what’s the chance of us spotting small insects and fungi – the things that really cause the problems?”

“The sheer volume of cut flowers and ornamental plants being traded at speed around the world makes it extremely difficult to intercept all the pests and diseases they carry. Even with the best of intentions, unwanted hitchhikers are getting through customs import checks all the time,” added Dr. Silviu Petrovan, a researcher from Cambridge.

Illegal plant trade and wild pests

The problem goes beyond pests. Some suppliers ignore regulations, illegally stripping orchids and cacti from tropical habitats and selling them as part of legal shipments. Enforcing trade protections on a large scale is challenging, making it easier for endangered species to be exploited.

“Even with a global trade in cultivated ornamental plants, there is still a market for rare species taken from the wild, and this can lead to rapid species declines, as well as increased risks that wild pests and plant diseases may enter the supply chain,” warned Dr. Amy Hinsley from the University of Oxford.

A frog’s journey to Sheffield

For Dr. Petrovan, the issue became personal when he was called to identify a live frog found in a florist’s shop in Sheffield. Initially, he assumed it was a joke. 

When Dr. Petrovan realized the tree frog had arrived from Colombia via Ecuador, he was shocked.

“Finding a South American tree frog in a Sheffield florist was extraordinary. It made me realize that if you can get this type of fragile small vertebrate arriving alive in a flower shipment without being noticed at customs, just how hard it must be to detect very small agricultural insect pests or their eggs,” said Dr. Petrovan.

To assess the scale of the problem, researchers analyzed records from Dutch customs (2017-2018) and the UK’s DEFRA (2021-2023). Over 80% of intercepted pests were insects, highlighting the difficulty of detection.

Environmental and health costs

The study on invasive species reveals several serious concerns about the ornamental plant trade, particularly in the countries that supply these plants. 

One major issue is pollution, as microplastics and agrochemicals used in plant cultivation contaminate soil and water systems. Another concern is the health risks faced by workers handling cut flowers which expose them to harmful pesticide residues. 

The industry’s high water consumption also threatens food security, especially in places like Kenya, where floriculture takes up to 98% of the water drawn from Lake Naivasha, reducing the availability of water for essential agriculture. 

Additionally, transporting flowers across the world generates significant carbon emissions, with each flower producing up to 3kg of CO2 due to refrigeration and shipping. Beyond these environmental impacts, the exploitation of wild plants remains a critical problem. 

Many endangered species, such as rare cacti, succulents, and orchids, continue to be taken from their natural habitats to meet demand, putting these species at further risk of extinction.

Need for sustainable solutions

Despite its risks, the ornamental plant industry supports many rural economies. In 2022, the global export value of cut flowers and foliage reached $10 billion, while live plants and bulbs totaled $13 billion.

“We absolutely don’t want to encourage knee-jerk reactions that might be well-meaning but actually cause more problems than they solve,” said Dr. Petrovan. Instead, he advocates for better industry standards. 

“We need to push to make the industry more sustainable through things like certifications and better regulation, and to work with those involved in the trade to better understand the risks and how to mitigate them,” added Dr. Petrovan.

The role of responsible consumers

“We need to be responsible consumers. While certification standards are being developed, buying plants rather than cut flowers can reduce many of the risks that stem from importing cut flowers. They last much longer and also reduce the emission costs,” said Dr. Alice Hughes from the University of Hong Kong (HKU).

The ornamental plant trade is booming, but it carries hidden risks. From invasive reptiles to agricultural pests, unchecked imports threaten ecosystems and food security. 

Smarter regulations, responsible sourcing, and consumer awareness can help create a more sustainable future – without sacrificing the beauty that plants and flowers bring to our lives.

The study is published in the journal Bioscience.

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