Adult Description: The Black Webspinner (Oligotoma nigra) is uniformly dark brown or black and typically 9mm in length. Only male Black Webspinners have wings and the ability to fly. Adult males also have an affinity to light. Females are typically more red in overall body color.
Larva Description: The Black Webspinner life cycle (egg, nymph and adult stages) is completed within a year. The nymph stage is able to construct an addition to the silk tunnel created by the parent. The nymph is pale or cream in appearance and becomes darker as it matures.
Host Plant: Lichens and moss
Ecological Threat: Although Oligotoma nigra are not known to pose an ecological threat, they are considered a pest when present in large densities. The Black Webspinner is usually only seen by humans when it is attracted to lights in the house in urban areas. As a ground feeder O. nigra often prefers dead plant material or nonvascular plants such as moss and lichen.
Biology: At all developmental stages O. nigra is able to produce silk sheets from silk glands located in the basal segment of the foretarsus. This ability to spin rapid silk tunnels creates a safe shelter from predators as well as a place to store food. Eggs are laid within the silk tunnel which expands when the eggs hatch. Nymphs build an additional tunnel to the established silk network. The silk tunnels created by the nymphs become larger as the insect grows. Oligotoma nigra is found in colonies due to the offspring additions to current silk tunnels.
The Black Webspinner has evolved anatomically to spend most of its life in the silk tunnels. This is demonstrated by a long slender body, developed rear muscles to allow for moving backwards quickly, and in males long oval wings to assist in backward movement.
History: It is believed that the Black Webspinner was brought to the United States in the late 1800's accidentally on a shipment of date palms shipped from Egypt or the Gulf Coast region.
U.S. Habitat: The Black Webspinner is a tropical species that dwells in a silk tunnel beneath a rock or large shelter at the base of a food source. The food source is often grasses or ornamental plants. Most of the Black Webspinner's life is spent within the silk tunnel.
Native Origin: India
U.S. Present: Oligotoma nigra is currently found in the southwest region of the United States ranging from Texas to California and as far north as Utah.
Oligotoma nigra closely resembles Oligotoma saundersii in color and overall body shape. The differentiating feature is a sickle shaped process on the 10th abdominal segment of Oligotoma saundersii.
As a ground dwelling species the Black Webspinner is often prayed upon by spiders and beetles. It is able to evade avian predators by retreating to the silk tunnel typically hidden under rocks or fallen logs. The Black Webspinner is also parasitized by tiny wasps of the family Scelionidae which acts as a brood parasite by laying eggs in the nests of the Black Webspinner.
Ross, Edward. The Embioptera of California. Bulletin of the California Insect Survey 6.3 (1957): 51-58.
Ross, Edward. A Synopsis of the Embiidina of the United States. Entomological Society of Washington. 86.1 (1984): 82-93