ON MAY 9th American customs and border-protection officials launched an aerostat—a fat, tethered balloon—above the coast of Puerto Rico. Its job is to use radar to detect low-flying aircraft, ships and smaller vessels carrying drugs across the seas to the south. This is not the first time the island, a territory of the United States, has been home to an aerostat: an earlier one crashed in a storm in 2011. Now it needs one again.

William Brownfield, the State Department’s senior anti-drugs official, says that 16% of cocaine imports into the United States came through the Caribbean islands last year. That is up from 4% in 2011. For European cocaine imports, the proportions are even higher.

The rising volume of drugs coming through the Caribbean is an example of what drugs wonks call the “balloon effect”, the idea that increased pressure on one drug route produces a bulge elsewhere. Until recently, the favoured northbound route for cocaine from South America—principally via Venezuela, after Colombia’s interdiction efforts in the 1990s—was by small aircraft to Honduras. Planes fly a dogleg path—first north, then west—to avoid Colombian airspace; the drugs then move by land or other means via Central America and Mexico.

Last year Honduras stepped up its counter-narcotics pressure. Drug flights to Central America dropped by a third and traffickers were pushed east to the Caribbean islands. That brings a chunk of the drug trade full circle, back to the 1980s when the likes of Pablo Escobar, a Colombian kingpin, used the islands as their route to market. It is “likely to get worse before it gets better”, Mr Brownfield told a group of Caribbean police commissioners in April.

Traffickers often work with small packages, moving them in several jumps (see map). Some embark directly from the Venezuelan coast; others go overland through sparsely populated rainforest in Guyana and Suriname, where borders are virtually uncontrolled and small aircraft can land on remote roads or interior airstrips.

The first hop from the mainland is often by “go-fast” speedboat, laden for long trips with drums of fuel as well as cocaine. Sometimes the cargo is just 50kg, sometimes more than a tonne. The shortest hop from Venezuela is just a matter of minutes to Trinidad. The busiest route is due north to the Dominican Republic (Haiti wins some business, but is chaotic even for traffickers). There are also well-established trails up the eastern Caribbean island chain and westward via Jamaica.

For the next leg of the journey, another option is to use drugs mules and swallowers of cocaine-filled condoms. A steady stream of yachts and pleasure craft ply the blue waters between the islands. A few cross the Atlantic, where European controls on arriving yachts are lax; a few sail north. Boat-to-boat transfers create confusion; customs checks are often lax. Cruise ships are attractive because screening is a nightmare. More than 6,000 passengers may board a single vessel after a busy day in port, some laden with shopping. There are also supplies, offloaded rubbish and crew to check.

Drugs are also concealed in commercial cargo. Big container ships call at transshipment ports such as Kingston in Jamaica or Freeport on Grand Bahama. In the Dominican Republic only one port, Caucedo, is certified under the Container Security Initiative that allows United States’ officials to examine cargoes. Smaller vessels of a few hundred tonnes chug from the mainland to the Dutch islands of Aruba or Curaçao, or from Guyana to the eastern Caribbean.

The final destination is likely to be North America or Europe, sometimes via West Africa. Puerto Rico is a way-station, physically in the Caribbean but within United States’ customs barriers. The French territories of Martinique, Guadeloupe and French Guiana do the same for Europe.

Backtrack

The uptick in volumes is nothing but bad news for the Caribbean. International gangs, from Mexico’s Sinaloa group to the Italian ’Ndrangheta, are becoming more entrenched. They work with local counterparts who may be paid in kind with a percentage of the shipment and perhaps a few guns. Local demand for cocaine is low; the main intra-island trade is in marijuana. But multiplying shipments mean more gang members and more officials to bribe. The Caribbean already has some of the world’s highest murder rates. The trafficking revival will do nothing to bring them down.