When South African officials at Cape Town’s international airport came across cardboard boxes labelled as toys being sent to China they became suspicious.

China is famous for exporting toys around the world - not importing them.

The boxes were opened for a spot check - and instead of finding the promised toddler’s cooking set or a board game inside, they discovered bundles of endangered succulent plants all carefully wrapped in toilet paper.

In total 23,000 plants known as conophytum were found in that consignment in April 2022, investigators with the Endangered Species Unit of the South African Police Service told the BBC.

The authorities had been on the alert after a courier company was nearly duped by the same ploy a few months earlier.

About a year later, the authorities at the same airport came across cardboard boxes labelled as mushrooms. They were also being exported to China.

When opened, they saw bags usually used for onions stuffed with succulents - around 12,000 pieces.

“It never stops,” said one police investigator. “You find out their one method, and they come up with another smuggling idea.”

Since 2019, more than one million illegally harvested succulents representing 650 different species have been seized by authorities as the plants transit through southern Africa to overseas markets, according to Traffic, an international organisation that investigates wildlife crimes.

It said that within South Africa, some 3,000 trafficked succulents are intercepted by enforcement agencies each week.

Driven by growing demand for them as ornamental plants, new markets are emerging, particularly across East Asia, with many African countries now involved in supplying them, largely from the wild, according to the South African National Biodiversity Institute.

This has threatened biodiversity in regions such as the Succulent Karoo - an area so-called by the World Wide Fund for Nature which covers extensive arid zones of South Africa and Namibia. It supports more than 6,000 succulent species - 40% of which are found nowhere else, conservation organisations say.

One of the most-common smuggled succulent species is the conophytum of which several sub-species are subject to trade restrictions.

This is because, according to the International Union for Conservation of Nature (IUCN) red list, they are either critically endangered or endangered.

And postal and courier services have become an easy way to smuggle small plants like succulents, wildlife trade experts say.

A recent report by the World Customs Organization (WCO) found that the most common method of smuggling flora and fauna was to pack them into small parcels to post, which accounted for 43% of all seizures in 2022 - an increase of 17% from the previous year.

“There are many different ways criminals may use to conceal illicit goods in the post. A common method is to use children’s toys,” said Dawn Wilkes, postal security programme manager for the Universal Postal Union - a global association of postal services.

She told the BBC such consignments generally originated from Africa or Asia.

And customs agents know all too well that traffickers are nothing if not cunning.

Last March, officials at Hai Phong city, in north-eastern Vietnam, discovered an intriguing shipment from Nigeria.

The containers were full of what looked like black horns. On closer examination, they found that were ivory tusks painted black.

Experts investigating illegal wildlife trade say it is unusual for tusks to be disguised with paint - though in the past Vietnamese authorities have seized ivory concealed in shipments of cow horns.

The Hai Phong seizure included some 550 pieces of elephant tusks, weighing nearly 1,600kg (252st).

It led to the arrest of two people in Nigeria in connection with the shipment, according to the Wildlife Justice Commission, which worked with the country’s customs service on the case.

The illegal trade in ivory mainly affects Angola, the Democratic Republic of the Congo, Kenya, Zambia, and Zimbabwe and is one of the major reasons behind a decline in African elephants – the population has fallen by around 90% over the past 30 years.

The African forest elephant is on the IUCN’s red list as critically endangered.

Endangered sharks off the coast of Africa are also proving difficult to protect -especially as their fins are a key ingredient in shark fin soup, a much sought-after delicacy in many parts of the world.

There are more than 500 recorded species of sharks, and the trade in many of them is allowed. But selling and buying parts of around 60 shark species is restricted as they have become endangered.

And this is the loophole traffickers exploit, wildlife trade investigators say.

A few cases were detected in South Africa in recent years when customs authorities were faced with shipments that included a mix of both legal and illegal shark fins.

“Criminals will claim that the endangered species are actually the legally traded species,” Sarah Vincent, an expert with Traffic, told the BBC.

“So it is vital that law enforcement know how to tell which is which.”

This was being done in South Africa with the aid of Traffic's 3D digital technology, she said.

Given that wildlife trafficking cases have become increasingly sophisticated with varied concealment methods, it is important for enforcement agencies to share information with their regional and international counterparts.

For Elizabeth John, senior wildlife investigator with Traffic in south-east Asia, a united front against traffickers is the only way to confront them.

More information-sharing over the years has resulted in increased seizures.

Confiscations in 2022 were up 10% compared to 2020 figures, and a striking 56% compared to 2021, according to a WCO report.

But increased seizures also point to an alarming trend.

“These statistics suggest that illegal wildlife and timber trade are still prevalent, and traffickers are employing various techniques which are evolving, to evade applicable laws that prohibit this illicit crime,” the WCO says.

Wildlife trade experts say the challenge is to keep customs and border control authorities well-resourced, equipped and trained to be ahead of the traffickers’ constantly evolving tactics.