Heptagonal orbweaver

Description

Heptagonal orbweaver is a common, exotic, small, orb-weaving spider. It was probably introduced into the United States from Australia or the Pacific islands, where it is native. It now occurs in the U.S. from Maine to Florida, west to Minnesota and eastern Texas, and on the West Coast of southern California. The first sighting in Minnesota was in Wabasha on June 21, 2019.

Adults are active from March to November. They are found in agricultural fields, old fields, marshes, and roadside ditches. Webs are built in vegetation near the ground.

Females are ⅛″ to ¼″ (4.1 to 6.0 mm) in length.

The front part of the body (cephalothorax) is much smaller than the abdomen. It is yellowish brown sometimes with yellow spots.

There are eight eyes arranged in two parallel rows of four eyes each, and in three groups, four in the middle and two on each side. The rear row is curved forward and the front row is straight or slightly curved backward. All of the eyes are small. The median ocular area (MOA), the area defined by the middle group of four eyes, is square or trapezoidal. On each side the lateral eyes are widely separated from the middle (median) eyes and are almost touching each other.

The abdomen has six bumps which make it appear to have seven sides (heptagonal) when viewed from above. This is the feature that gives the species its common name and its species epithet. The coloration of the upper surface is variable. It is usually dark brown or yellowish brown, there is usually a dark triangular area near the rear, and there are sometimes white markings. The background color of the abdomen is sometimes mostly white or pale with a mesh-like network of thin brown lines.

The legs are yellowish brown with dark bands.

Males are slightly smaller, 3⁄32″ to 3⁄16″ (2.6 to 5.3 mm) in length. The carapace and legs are yellowish brown. The abdomen is smaller and paler, and the dark mark near the rear is distinct.

Size

Female Body Length: ⅛″ to ¼″ (4.1 to 6.0 mm)

Male Body Length: 3⁄32″ to 3⁄16″ (2.6 to 5.3 mm)

Web

The female constructs a dense, vertical web of sticky threads close to the ground between herbaceous plants. The web is up to 3″ (13 cm) in diameter and consists of 25 to 33 radii and numerous spirals.

Similar Species

Habitat

Agricultural fields, old fields, marshes, and roadside ditches

Ecology

Season

March to November

Behavior

Life Cycle

Food

Small invertebrates