Jersey Shore goers know all too well that nothing can ruin a day at the beach quite like those pesky greenhead flies whose bites pack quite a punch.

What are greenheads?

Greenheads, which are produced from our coastal marshes, are a species of horse fly whose scientific name is "Tabanus nigrovittatus", which in Latin, translates to “black striped horsefly,” said Kyle Rossner, a South Jersey entomologist with a background in insect conservation.

The greenheads that bite are the females that are seeking a blood meal to produce eggs. Those eggs are laid and the larvae develop in salt marshes along the high tide line where vegetation collects. Their larvae are predatory maggots that feed on other invertebrates, Rossner added.

The females need the proteins and fats that are rich in mammal or bird blood or even reptile blood. They use that to produce their egg masses that require a lot of protein and fats.

Rossner said the larvae of greenheads get enough of that in their larvae diet. The first batch of eggs for greenheads is laid without any blood. But in order to produce subsequent batches of eggs, the females need to seek out another source of that protein.

'It’s just a regular old buffet of people with their clothes mostly off'

What attracts greenheads to the beaches?

That would be the abundance of food at the beaches, which is humans, Rossner said.

“It’s just a regular old buffet of people with their clothes mostly off, so a lot of space to bite,” he added.

The salt marsh greenhead is in full force. Greenhead fly populations reach peak numbers in July but they are out and about from mid-late June into September, Rossner said.

The females bite from sunrise to sunset with bites reaching their peak in the middle of the day when it’s high heat and humidity. Rossner said the only time he’s never seen the greenheads bite is at night.


Does wind direction affect their presence?

Wind direction and speed can affect how many greenheads are in any particular area. He said that has more of an effect when you get further from the marsh. So, the closer to the marsh, the less it’s going to have an effect because that’s where the flies are generally.

When talking about beaches, it’s important to compare towns and the amount of space they have between the marsh and the ocean.

For example, in Wildwood Crest, if the wind is blowing from the ocean to the marsh, it’s less likely the greenheads will make their way from the marsh to the oceanside, Rossner said.

But, in Strathmere or Stone Harbor Point, the marsh and the ocean beach are very close to one another. Greenheads are strong fliers and big insects so wind direction is not going to deter them much from making it to the beach, he said.

At Sandy Hook, breezes blowing from the bay toward the ocean could bring out more flies.

Can greenhead flies transmit disease to humans?

Generally, humans can be worry-free about disease transmission from greenhead flies, Rossner said.

“The thing you should watch out for the most with them is the big welts, the bites that they leave. They can easily become infected if you don’t keep them clean or you keep scratching them open. I always find if you have one or two of them, putting a bandage over it keeps you from scratching it,” he said.

Greenheads can spread infection to cattle and they carry equine encephalitis that can affect horses.

How can humans stop getting bitten by greenheads?

Greenhead flies are attracted to many things like body heat, movement, and certain colors.

Rossner said the best defense against greenheads that works for him is wearing light-colored, long-sleeved shirts and long pants. Finding the right combination of fit, color, and fabric can keep them away and keep you incredibly cool.

Since that’s not the perfect outfit for the beach, Rossner suggested wearing repellant with DEET. While DEET won’t stop the flies from landing on a beachgoer, it can stop them from biting.

Can people trap greenheads?

It’s difficult to keep greenheads out of our backyards with pesticides because they are strong, big insects. So, it would require heavy doses of pesticides that would not only be expensive but would cause ecological problems, too, Rossner said.

But there has been a lot of good luck and research into greenhead traps that are in people’s yards. They are big black boxes on four legs with two big jars sticking out of the top of them.

“There is some good information with plans on how to build those yourself online and even through the Rutgers website. But, then also there are people throughout southern New Jersey who are selling them pre-made,” Rossner said.

So, until it’s time to go back to school, greenheads are here to enjoy the summer with you at the shore.

Jen Ursillo is a reporter and anchor for New Jersey 101.5. You can reach her at

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