Are Joro Spiders and Other Invasive Insects Headed to Central NJ?

By Richard D. Smith | Posted July 11, 2024

Invasive plants and insects are with us. And some have been around long enough to become residents. Too often that’s disastrous, as witnessed with the emerald ash borer of East Asia, which possibly became established in America in the 1980s. It was first documented in New Jersey in 2014. In just ten years, it’s become a scourge. According to the U.S. Forest Service, the insect has killed tens of millions of ash trees of every variety and is on track to eliminate most of North America’s 8.7 billion ash.

A female joro spider tends her web. The spiders are expected to arrive in New Jersey this summer.

(Photo by David Coyle, Clemson University.)

Meanwhile, other established invasives have receded into local ecosystems, becoming pests more than catastrophic threats. Are their populations being held down by existing predators or fluctuations in temperatures or food supply? It’s not often clear.

For example, so far this summer in Rocky Hill (about the geographical center of The Montgomery News readership area), surprisingly few brown marmorated stink bugs are to be found, in nature or within houses. George Hamilton, extension specialist in pest management at Rutgers University, New Brunswick, confirms that the stinkbugs “have been at lower levels for some time. For the most part, except in some agricultural situations, they are now more of a background insect.”

And what of the notorious spotted lantern flies, a serious threat to vineyards and other fields of succulent fruits? They, too, seemed mysteriously absent until early June when a Rocky Hill-based journalist observed (and then promptly squashed) two lone SLF nymphs.

“Same comment about spotted lanternfly, although they are still around,” said Prof. Hamilton, who’s observed SLF nymphs feeding on multiflora rose bushes in the woods near N.J. State Police headquarters, West Trenton. But he cautioned: “In other places, like Hudson County, they are still a big nuisance.”

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By contrast, milkweed bugs – with their characteristic lozengeshaped black bodies and inverted orange-red V marking — aren't invasive nor hazardous. But they mated prodigiously in April, giving rise to vigorous nymph hatches in late May/early June, with the prospect of multitudinous adults come July. Prof. Hamilton confirmed this report, adding that their abundance might portend local ecosystem health. “I would say they are a good indication that there are milkweed plants nearby, which is also good for insects like Monarch butterflies.”

But what of the scariest insect — actually, an arachnid — now in the news: the joro spider? Like the spotted lanternfly, they probably arrived from their native East Asia in a shipment of goods. They first became established in Georgia a decade ago.

Some scientists predict they’ll arrive in New Jersey this year. “It’s possible that they will eventually get here,” Prof. Hamilton acknowledged, “but I doubt it will be this year. If they do, they’d probably be hitch-hiking on a truck or car coming up from the Deep South.”

Most experts report that joro spiders aren’t aggressive, and even if they do bite, their venom is too weak to endanger humans. But the females with their bright yellow markings and expansive size (about that of a human hand when their long legs are extended) could terribly frighten people during a first encounter. “They probably will,” acknowledged Prof. Hamilton. “But so do the big wolf spiders in peoples’ basements — including mine.”