Each year, the first few weeks of fall in South Jersey feature an invasion from the north — monarch butterflies, descending on the shore en masse as they migrate south to Mexico.

But this year, the invasion has become a deluge, with the most butterflies seen in years in parks, refuges and even in towns. Visitors and residents are crowding shore areas to see.

So one of the shoulder season’s biggest attractions turns out to be not a convention or a festival, but an insect converging on the region by the thousands.

“I think every time I look up, I see a monarch,” said Don Freiday, visitor services manager at the Edwin B. Forsythe National Wildlife Refuge in Galloway Township.

In Cape May Point, the Monarch Monitoring Project has been doing hourly and weekly counts of monarch activity for 20 years. Halfway through the season, numbers for last week show an average of 237 monarchs spotted per hour, the highest average for that week in six years and the third highest in all 20 years.

“We’re coming up on seaside goldenrod time, and Cape May Point’s going to be gangbusters when the winds come,” said Monarch Monitoring Project field coordinator Louise Zemaitis, of West Cape May. “People have been flocking there by the hundreds to see monarchs the last couple of weekends.”

Cape May Point State Park, at the very southern tip of the state, is the last spot monarchs can gather before they make the long trip across the Delaware Bay to the south, making it one of the biggest draws for monarch observers.

While this week was slower due to rainy weather and southerly winds — keeping the monarchs from starting out across the bay — the weekend’s conditions look so favorable for seeing butterflies that visitors may see a “river of monarchs” making its way through the dunes.

“It continues until the end of October,” Zemaitis said. “They come from anywhere there’s milkweed — that’s their host plant. Without milkweed, there’s no monarchs — in places like southern Canada. They’re a tropical species and can’t survive any freezing temperatures, so they go to the mountains of Mexico outside Mexico City, and they rest there by the millions.”

Why so many this year? Zemaitis thinks low numbers last year may have been due to a wetter season that led to fungus and disease killing off the larvae.

“Insects have the ability to rebound from relatively low numbers,” she said. “We’ve had some years that were really, really bad, and this year seems to be (better).

Also this year, the central flyway away from the shore is experiencing drought, she added, driving more to the eastern flyway through New Jersey — “which seems to be OK and full of monarchs.”

As they make their annual migration south — often multiple generations removed from those who came the year before — a dual migration of monarch enthusiasts arrives to greet them.

“Over the last three to four weeks, I’d say 40 (percent) to 50 percent of visitors come to see the monarchs,” said Janet Hunnicutt, who works in visitor services at Cape May Point State Park. “On the trails where we have wild sunflowers, they converge out there pretty well, and in the back behind the dunes on the goldenrod.”

Timing is everything, Hunnicutt said.

“If you get here really early, you can see them roosting,” she said. “And then around 11 to 12 (in the morning), they become super-active.”

At the Forsythe refuge, Freiday estimated, “I’d have to say there are three or four times as many as I’ve seen. ... Last Friday we went on our nature walk, and there were dozens roosting in the trees along the sides of the trail.”

Tim and Vici Shull, of Moorestown, Burlington County, visited the refuge this week, and while they’re mostly birders — waterfowlers, to be precise — they hoped to study up on the monarch.

“One of the things I’ve tried to do is become more knowledgeable of butterflies,” Tim Shull said. “I’m still a novice when it comes to them. I’m doing pretty good with birding, but with butterflies, we’ve barely scratched the surface.”

Added Vici Shull: “They fly by so quickly, you can’t see them!”

The dual birder/monarch watchers are part of a trend of visitors to the shore, said John Cooke, president of the Chamber of Commerce of Greater Cape May.

“The whole ecotourism niche market Cape May offers is a very attractive draw for naturalists,” Cooke said. “And it’s helped all the hospitality people fill the gaps during the shoulder season.”

As for the monarchs themselves, it won’t really be known just how many came this way until they do a count over the winter in Mexico — “where they count by the hectare,” Zemaitis said.

“Monarchs are interesting on many levels,” she said. “Scientifically they’re quite interesting, but another is the mystical way that some people look at it. They arrive around the Day of the Dead in Mexico, and they look at monarchs as the souls of the dead. When they return to the mountains, they feel like they’re with their loved ones. And I feel many people up here feel that way, too.”

Contact Steven Lemongello:

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