It is early morning when we arrive at the rugged coast of Aruba’s Arikok National Park. My intrepid guide for the day is Diego Marquez, the park’s director and former biologist. Our mission is to find boa constrictors. "Even though this area is extremely arid, humidity hangs under the bushes and trees," says Marquez. "Much of it is produced from sea spray blown in by the trade winds. Boas thrive in this place. Let’s go find one."

Marquez leads me over a treacherous, trail-less limestone landscape dotted with scrub and stout trees sculpted horizontally by the winds. I try to avoid the barbs, needles and thorns that seem to be poking out from every plant. "Watch out for the thistles, too,” warns Marquez. "If you brush up against one of those, you will get a bad chemical burn." And then there is the unforgiving terrain. Any misstep here and chances are good for a twisted ankle, or worse. I want to view this hauntingly beautiful place while walking, but that is out of the question. I can only focus on the next step and where to place my feet. After a tedious five minutes, we stop in front of a huliba tree. "Welcome to the Boa Forest. Can you find the snake here?" asks Marquez. I scan the dense maze of dried limbs and sparse branches. After a half minute, I give up. "Okay, where is the boa?" I ask.

Diego Marquez Boa 27 02 2014
As director of Aruba’s Arikok National Park, biologist Diego Marquez is used to tracking down the boa constrictors that have invaded the island. Image: Patrick Holian

Marquez points to the base of the tree's gnarly trunk with his snake-handling tool. Lurking motionless in the shadows is a metre-long boa constrictor. I'm a bit miffed – I'm no more than three feet away from it, and yet I've missed it. "Don’t worry," says Marquez. "If a ranger finds one snake an hour, that’s about average. The snakes blend into the habitat very well. You can go very close to them and they will not move. Finding a boa is tricky business."

I learn that boa constrictors are ambush predators, ones that normally do not travel to hunt. Instead, they wait for prey to come to them. Positioned head down at the base of the tree, the snake we've just uncovered can easily strike at lizards sccurying by.

We hike for another half hour. I pass directly underneath a huge snake curled on a tree branch and don't even see it ... Marquez has to call me back, pointing upwards. "This is another common ambush place. Boas often stretch out on branches so they can nab birds.  I also find them lying under shrubs. The snakes conceal their entire bodies under the leaf litter, except for their heads. Then they wait for a bird or lizard to come by."

Twenty years ago, there were no boa constrictors roaming the Aruban countryside. Then one day in 1999, the first one was discovered. Depending on her size, a mother boa can give birth to 30-50 baby snakes at a time. With no natural predators on the island, the population has exploded in a very short time. 

“Their adaptability is how nature works and that’s beautiful. When you see those snakes, they are trying to survive just like us.”

"We were studying the cascabel, Aruba’s rare rattlesnake," says Andrew Odum, a Toledo (USA) Zoological Society herpetologist who has been conducting snake research here for over a decade. "It’s unique in the world, but once we discovered the invasion of boa constrictors, our focus changed. We need to find out the exact impact boas are having on Aruba's native species and develop a management plan."

I later speak with Facundo Franken from Aruba’s Section of Nature Management. "It’s most likely the first boas were released by or escaped from snake hobbyists," he says. Franken is also a member of the Boa Constrictor Task Force, a volunteer group that conducts annual boa hunts to keep numbers down. Boas are not restricted to the park, but are found all over Aruba, from local backyards and hotel gardens to the front steps of the island's Parliament. In 2008, over 800 were captured. Experts believe four to five times that number are still on the loose.

Franken has a unique take on these island invaders. "Their adaptability is how nature works and that’s beautiful. When you see those snakes, they are trying to survive just like us.  And we don’t belong here either if you want to really look at the situation. If you are making excuses for people, why wouldn’t you do that for a species?"

Aruba Habitat Fragmentation 27 02 2014
Development on the island has fragmented what used to be vast stretches of wild outback. Image: Patrick Holian

Franken is referring to Aruba's relentless development to accommodate a burgeoning tourism industry and a fast-growing population. Two large photos that hang at Arikok National Park's visitors' centre illustrate the problem clearly: a 1948 aerial shows post-World War II Aruba, while beneath it hangs a digital satellite image of the island 50 years later. The difference is staggering. Areas that were at one time cunucus (small farms) are now crammed with housing developments. Vast expanses of Aruba’s mondi (the island’s wild outback) are now a checkerboard mosaic of human encroachment. In short, the natural habitat of this small island nation is quickly disappearing. And it seems people are more responsible for the 'big squeeze' on Aruba’s environment than the boa constrictors are. 

"We have human behaviour with unplanned development with no recognition of nature. It is causing fragmentation of the habitat," claims Greg Peterson, founder of the Aruba Birdlife Conservation Foundation. "Aruba has gone into an unsustainable development. It has gone from 60,000 to 110,000 residents in one generation and the results are severely impacting our bird populations, our environment."

Shoko Burrowing Owl 27 02 2014
Populations of the shoko, a type of burrowing owl found only on Aruba, have been particularly affected by the boa invasion. Image: Albert Burgers, Flickr

Peterson and Marquez did some data crunching with what they consider conservative numbers and estimate that over 17,000 birds are devoured annually by boa constrictors.  One bird hit hard is the shoko, a burrowing owl subspecies found only on Aruba. Peterson recently dissected a freshly killed boa and found four shokos, an entire family, in the belly of the snake. World-renowned avian biologist Adrian Del Nevo pegs Aruba's shoko population at around 200 pairs. The owl-eating boa that Peterson opened, therefore, ate 1% of the population at one sitting.

Back at Arikok National Park, Diego Marquez and I conclude our trek in the 'Boa Forest'.  We uncover three boa constrictors in our hour-long search. He leaves me with this parting thought about the invasion. "We need daily patrols in high-density areas, places like roois (arroyos) in the city. They are perfect places for the snakes since they hold plenty of water and birds. But until the Aruban government gets that in place, we can’t effectively control the boa."

Aruba has a Minister of Environment, but no department to handle a bio-invasion on this scale. It's akin to having a steering wheel but no car. In addition, the annual volunteer boa hunts are simply not keeping pace with the exploding snake population. There also appears to be little political will to power down the robust economic engine of tourism and development. Until the actions of both snakes and humans are to some degree restrained, the big squeeze on Aruba’s natural world looks set to continue.

Top header image: Nick J Webb, Flickr