New Jersey Butterfly Sites

Glenhurst Preserve and Wagner Farm

by Mike Newlon

County: Somerset.

Municipality: Warren Township.

Directions: From I-78, take exit 36 (King George Road) and drive south 0.2 miles south to the stop light at Mountain Avenue. Turn left and drive 1 mile to the entrance (just past a small bridge) on the left. At the parking area there is a kiosk with information about the site and a trail map.

Parking: Yes, at both sites.

Nearest sizable town: Warrenville, a few miles south on King George Road, has shopping centers and restaurants. The closest gas station is on King George Road, immediately north of I-78 and there is another in the direction of Warrenville.

Habitats: Old fields, grown up to varying extent, cedar groves, a stream, ponds, forest edge, the Passaic River.

Maintained/Marked trails: Yes, although recently mowing has been episodic and trails may be grown up knee-high (or higher). Trails may also be rutted from passage of mowing equipment. Off-trail walking may be difficult because of thick vegetation and tussocky ground.

Restrooms: None at Glenhurst Preserve. In the warmer months there is a portable toilet at Wagner Farm (see below).

Picnic tables: No.

Species (notable in bold): Black Swallowtail, Eastern Tiger Swallowtail, Spicebush Swallowtail, Cabbage White, Clouded Sulphur, Orange Sulphur, Banded Hairstreak, Hickory Hairstreak, Striped Hairstreak, Juniper Hairstreak, Gray Hairstreak, Red-banded Hairstreak, Eastern Tailed-Blue, Summer Azure (can be abundant in June; native dogwoods, their host plants, are common), Great Spangled Fritillary, Pearl Crescent, Question Mark, Eastern Comma, American Lady, Painted Lady (some years), Red Admiral, Red-spotted Purple, Viceroy, Appalachian Brown, Little Wood-Satyr, Common Wood-Nymph, Monarch, Horace’s Duskywing, Wild Indigo Duskywing, Silver-spotted Skipper, Common Checkered-Skipper (once), Least Skipper, Fiery Skipper (some years), Peck’s Skipper, Tawny-edged Skipper, Northern Broken-Dash, Little Glassywing, Sachem (some years), Delaware Skipper, Hobomok Skipper, Zabulon Skipper, Broad-winged Skipper, Dun Skipper, Ocola Skipper (some years).

Best time to visit: June through August for butterflies; any time of year for birds, although fall migration can be especially good.

Exploring Glenhurst Preserve: From the Glenhurst parking area continue straight ahead through the gate. A large area of old fields and thickets lies ahead of you. The Red Trail (consult the map on the kiosk or available here) follows the perimeter of this area and is the best trail for butterflies on the tract. Early in the day the west side of the red trail, straight north from the parking lot, catches the sun early, while the trail on the east side of the area is still in shade. When you reach the Cross Trail in about 100 yards you have the option of continuing north to reach the ponds and the Passaic River, or crossing over to the east side. If there has been heavy precipitation recently the latter may be the best option. The cross trail to the east soon climbs up a small mound that in summer has had a patch of Canada thistle that attracts hairstreaks and skippers in midsummer. [You can also turn west here; cross Corey’s Brook on a small bridge; cross the trail that runs up the west side of the brook, bear slightly left on an ill-maintained trail through a screen of trees to reach a clearing which in late summer has abundant Joe Pye Weed and Ironweed.] Recently there has been a large patch of Purple loosestrife in the SE corner of the red-trail loop which in late summer attracts swallowtails, skippers, and other butterflies.

Exploring Wagner Farms: To reach Wagner Farm, return to Mountain Avenue, turn right, and drive 0.2 miles to the unmarked gravel driveway, between the fenced Community Garden and the silo. Cabbage Whites and Sulfurs are abundant in the extensive meadows here. Recently the upper part of the meadow has been mowed frequently, making it unattractive to butterflies. If mowing has not been recent patches of thistle and milkweed may attract them. It is usually worth walking around the community-garden fence.

Special precautions: Glenhurst Preserve, once a farm and then a golf course, slopes from Mountain Avenue down to the Passaic River. The tract offers the best access to a large area of protected land along the Passaic. The lower parts are often muddy and sometimes under water. Rubber boots are handy in getting through tall vegetation, especially if you wish to get off-trail, and often necessary. Ticks are present so take appropriate precautions. Parts of the south side of the Glenhurst tract abut private property. The border is usually obvious. DO NOT TRESPASS.

You might also want to visit: Great Swamp National Wildlife Refuge.

Further Information: Glenhurst Preserve (formerly known as Glenhurst Meadows) is a well-known birding site, especially good in fall. Birders may wish to consult the ebird hotspot. In recent years Red-headed woodpeckers have been regular along the Passaic River; listen for their soft three-note rattle. The area is briefly described on p. 179 of W.J. Boyle’s A Guide to Bird Finding in New Jersey, second edition, following the entry on Lord Stirling Park.



To view a larger map, click on 'View larger map' icon in upper right hand corner. (Tip: The satellite view may also suggest good potential butterfly habitat to explore.)


Glenhurst Preserve sign

Glenhurst Preserve sign.


Glenhurst Preserve trail

Glenhurst Preserve trail.


Wagner Farm meadows

Wagner Farm meadows.