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July: Fiddler Crabs

Fiddler crabs are a key indicator of the health of the region's salt marshes.

fiddler crabs

Watch the tide ebb at any salt marsh in the Harbor Bight area, and chances are you'll be treated to sightings of fiddler crabs, one of nature's more vivid characters. Fiddlers emerge from burrows in the mud as the tide recedes, to skitter about -- foraging, mating, and doing burrow-construction and maintenance work.

The first thing you'll notice about fiddlers is that some of them sport one outsize yellow claw that, while impressive, seems far too big for the crab's small body. These are the males, and, in fact, these claws do hinder a male fiddler's search for food. On the other hand, they seem to be an important part of his sex appeal. (Perhaps the bigger the claw, the more gumption that particular male must have simply to survive, a quality that doesn't go unnoticed by the females!) During the summer, when fiddlers breed as frequently as once every two weeks, a male puts much effort into digging and maintaining a large, tidy cylindrical burrow fit for his hoped-for queen. Most of the rest of his energy goes into trying to seduce a female -- he waves his big claw about, trying to get a female's attention, and then tries to escort each prospect down into his burrow. If a female seems interested, he'll descend partway into the burrow and drum its edge with his claw. If she likes these "good vibrations," she will enter the burrow, the male will plug up the entrance, and they mate.

All burrows provide shade and refuge during the hottest parts of the day, during winter (fiddler crabs hibernate through the cold months) and during high tide. Fiddlers will roll up a small amount of mud and plug up their burrow's opening during high tide, trapping a small pocket of air. When the tide rolls out, holes will suddenly begin to appear in mud as it is exposed, and fiddlers emerge.

fiddler crabFiddlers roam the flats of salt marshes in search of algae or decaying vegetation. Unlike other crabs, which use their claws, or "chelipeds," to crush food or to grasp objects, the fiddlers' claws are used to pick up sand or mud, which they ingest. They use their mouthparts to scrape food materials (such as decaying organic matter and unicellular plants such as algae) from the sediment. Then they place indigestible material aside in the form of balls. These undigested pellets often blanket the marsh, and can persist through successive tidal cycles.

Fiddler crabs are a crucial link in the ecology of a salt marsh. They help aerate the soil around marsh grasses and stimulate the turnover of important nutrients in the soil. Fiddlers are also a favorite prey of larger predators such as blue crabs, egrets and herons, and small mammals such as raccoons. And they are also sensitive to environmental contaminants such as insecticides and heavy metals.

Where to See Them: Fiddler crabs can be seen in most tidal salt marshes and associated mudflats along the New Jersey coast and in Long Island. Good examples of salt marsh habitat are found at New Jersey's Cheesequake State Park and Forsythe Wildlife Refuge, and New York's Pelham Bay Park and Jamaica Bay Wildlife Refuge.

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More Highlights Planting butterfly gardens is a great way to build a tiny nature reserve in your own backyard. A successful butterfly garden has plants that meet butterflies' needs during all four life stages -- egg, caterpillar, chrysalis, and adult.

You can attract butterflies to your garden by providing them with food (nectar-rich flowers), water, shelter, and places to lay their eggs (host plants). Different species of butterflies can have very different tastes in nectar; the greater diversity of flowering plants in your garden, the greater diversity of butterflies you'll likely attract. (Some plants, such as milkweed and butterfly bush, attract a wide variety of butterfly species.)

Note also that caterpillars eat the foliage of the plant they were deposited on as eggs, which means you'll need to grow plants that female butterflies prefer to lay their eggs on.

black swallowtail larva on Queen Anne's lace

Photos: Don Riepe/Jamaica Bay Wildlife Refuge

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