Foliage Webbing Spider

Introduction

Young Foliage Webbing Spiders delay their dispersal and live together in communal nests built on plant foliage until they reach the subadult stage.

Identification

These spiders are silvery grey to brown in colour with a contrasting pattern of light and dark brown markings on the abdomen. The genus is related to the black house spiders (Badumna spp).

Habitat

Found on foliage, in communal nests when young.

Distribution

The foliage webbing spider is a widespread species. It is found in open forest, woodland and shrubland throughout much of mainland Australia. A closely related, non-communal species is found in Tasmania (Phryganoporus vandiemani).

Feeding and diet

The communal nest consists of an inner retreat area with numerous entrance holes opening into a network of connecting passages, and an outer area made up of ladder-like layers of cribellate silk where prey is captured.

Other behaviours and adaptations

Foliage webbing spiders are unusual in having a periodic-social life-cycle, that is, one that includes a period when the spiders live together socially, followed by a period when they live alone. Throughout summer, spiders leave their communal nests to take up solitary lives. The females leave first, as subadults, whereas the males leave somewhat later, mostly as adults. This reduces the likelihood of nest-mates interbreeding and promotes gene exchange in the population.

The communal nests vary greatly in size and number of occupants. The nests of an intensively studied Queensland population had from 9 to 224 spider occupants. A football-sized nest from the Victorian mallee region contained 661 spiders (558 juveniles, 40 males and 23 females). Larger nests attract a wide range of arthropod parasites, predators and scavengers. Some of these may attack the host spider's eggs and young and contribute to the reduction or failure of some colonies.

Social interaction is most highly developed between juvenile spiders and less so between the dispersing stages of subadults and adults. Juveniles will cluster together and undertake collective tasks such as nest construction and cleaning, capture of food, and feeding. However, the juveniles may behave cooperatively because they are giving out hormonal chemicals (or pheromones) at this time which promote toleration. This is different from the truly cooperative behaviour shown by spiders and insects that are permanently social.

Life history cycle

Solitary females build their small, irregular, sheet web with sac-like retreat tubes on the foliage of shrubs (often spiky species) and small trees such as mallee eucalypts. After mating, a female produces up to 16 lens-shaped egg sacs over several months, each containing between 10 and 40 eggs. After the spiderlings emerge from the egg sacs their dispersal is delayed. Consequently, they stay together as a colony until the following summer. By then, the spiders have reached the subadult stage and begin to disperse from the nest.

Economic impacts

In past years orchardists in south-eastern Australia complained of foliage matting, leaf fall and limb damage caused by infestations of foliage webbing spiders. Orchard pests such as thrips can shelter within the nests where they are protected from pesticide sprays. Graziers in western New South Wales occasionally complain that shrubby native fodder plants become unpalatable for cattle or sheep because they are festooned with the silk nests. In such agricultural situations spiders can also be useful biological control agents, capturing pest insects.