What are those Blue Boxes in the Marsh?

Posted by Mark Washburn on Wednesday, February 18th, 2015 at 9:53am


There’s something on Cape Cod that at first probably looks a little out of place to the first-time visitor.  It’s not a tourist spot, or even a scenic part of the Cape, but it is an important one.  We’re talking about those bright blue boxes you’re sure to spot mixed in with the green marsh grass.

Essentially, these strange wooden boxes are part of an effort to control a not-so-welcome visitor.  Each year, the months of July and August are seemingly the worst for enticing the annoying greenhead fly.  This is the time of year unfortunately that the females bite many residents and visitors, leaving behind a large itchy welt.

The female can lay up to 200 eggs at a time, but needs blood to lay more eggs.  That’s why she starts looking for people and animals, and has no mercy on those she chooses to attack.  It’s an annoying inconvenience for beachgoers, boaters and hikers, alike.  That’s where the blue boxes come into play.

These blue boxes are part of the Cape Cod Greenhead Fly Control Project.  Essentially, around springtime or early summertime, fly trappers set out hundreds of these boxes in the marshy areas of the Cape.  Not only do they spare people from being bitten, but also they actually trap the greenhead flies inside.  On average, the boxes collect hundreds of thousands of greenhead flies by the end of the season.

Most flies are attracted to the color blue, but other designs are also in operation.  They all work pretty much the same way.  The contraptions help lure the greenhead flies under and up, as if they were about to strike a large animal.  Unfortunately for the flies, once they get inside the boxes they can’t get out.

If you’re wondering why the area isn’t just sprayed with some type of chemical to help control the fly population, there’s a good reason.  It’s part of an effort to preserve the surroundings.  Because there are so many greenhead flies in the area, and they’re so large, it would take a huge amount of chemicals.  Those chemicals could hurt the marshland, and perhaps not impact the fly population at all.

To help keep the Cape a fun and enjoyable place to be, the blue boxes aim to reduce the numbers and reduce the bites.  Scientists are continually coming up with new ideas to try to make the traps better and more effective.  That’s good for all of us hoping for an enjoyable summer along Cape Cod.

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