Goodbye Greenheads!

Have you ever gone into a marsh in Cape Cod or have just been sitting on the beach when all of a sudden you get a pinch of pain? And then, hours later, that bite becomes raised and it starts to painfully itch and ooze? What could have possibly happened? You were bitten by a greenhead.


What are Greenheads?

More harmful than mosquitos (in my opinion), greenheads look like normal flies, but seconds after they land on you, they inject their saliva into your blood causing a painful reaction. Greenheads, or salt marsh horse flies, are actually two different species of flies including Tabanus nigrovittatus and Tabanus conterminous. Both species can be found in salt marshes along the Atlantic coast, from Nova Scotia all the way to Florida. These flies are most abundant during the summer, which is not good for the tourism industry in Cape Cod.

Greenheads spend their whole lives in and around the salt marsh. They lay eggs on salt marsh grass and the larvae either crawl down after hatching or get washed away by the tide. The larvae then burrow in the marsh for 1-2 years. Then, the larvae come to the surface to pupate. Adult male and female flies feed on sugary substances, but after laying eggs for the first time, females get bloodlust.


Bloodcurdling Behaviors

In order to lay eggs again, female greenheads need blood for the same reason that female mosquitoes need blood. The blood provides much needed protein that is used in egg development. So, female greenheads must search for blood. Unfortunately for us, humans are usually the victims. Since greenheads are active during the summer months, beachgoers are an easy target.

Greenhead bites hurt so much because female greenheads inject their saliva into your skin and the chemicals within the saliva prevent your blood from clotting or scabbing. The pain is your body’s reaction to the chemical. The large bump is your continued allergic reaction.


How do they even find you?

Female greenheads do not only see you, but they can also smell you. Every time you exhale, they can smell the carbon dioxide and other chemicals that you breathe out. So, they can essentially find you day or night. Hopefully you aren’t sleeping in a room with one in it!


How can we control them?

The Cape Cod Greenhead Fly Control Project has implemented blue box traps. These traps only attract females that are looking for a bloodmeal. The box visually attracts them and each year, over 800 traps are deployed throughout Cape Cod.

All of the box traps are placed in the marsh. If you want to see one, visit our instagram (@beach.lex, or linked to our website). I went into the marsh and I was able to look at one in person. Since the majority of flies live in the marsh, they are the most effective when placed there as opposed to being placed in yards or on the beach. The traps are blue because blue has proven to be the most attractive color for blood-seeking greenheads. At the end of each summer, over 30,000 flies can be found in each box!

As greenhead populations have skyrocketed over the past 40 years, controlling them has become more and more necessary. By using the box trap, we are able to make the Cape as fun and enjoyable as possible.


This information is from this very interesting article:

https://www.ccmcp.net/greenhead-fly-control/pages/control-project-activities

Go check it out for more!


Cover photo: https://historicipswich.org/2019/07/21/life-in-the-time-of-greenheads/

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