Egg sacs and maternal care
The long thread helps keep this Tama egg sac safe from predators like ants. Photo: M Gray © Australian Museum.
A Jumping Spider has placed its eggs inside this combined silken retreat and egg sac. Photo: © R Morrison.
Female Wolf spider with young and egg sac. Photo: John Fields.
Uloborid Stick Spider (Miagrammopes sp.) on its web with an egg sac. Photo: M Gray © Australian Museum.
The egg sac silk protects the eggs against physical damage and excessive drying, wetting or heating, as well as providing a shield against predators like ants and birds. However, this protection is often breached by parasitic wasps, flies and mantispid lacewings that succeed in laying their eggs or infiltrating their larvae among or within the spider's eggs. Spiders like redbacks lay many eggs and make several egg sacs to ensure that enough eggs survive these seasonal onslaughts.
The eggs of many spiders are glutinous and stick together allowing them to be laid in a continuous stream into the partly built silk egg sac. They vary in colour from pearly white to green and in number from 4 to 600 in a single egg sac, depending on the species concerned.
Egg sacs come in all shapes, sizes and colours. They may be built inside a burrow (e.g, trapdoor spiders), under bark (e.g, huntsman spiders), in the web (e.g., black house spiders), in a curled leaf (e.g., leaf curlers), suspended on a long line (two-tailed spiders), or hidden among foliage (e,g., orb weavers). Some spiders stay with the egg sac, guarding it until the spiderlings emerge (e.g, huntsman spiders, trapdoor spiders) or carry the egg sac about with them (wolf spiders and water spiders), sometimes in their jaws (daddy-long-legs spiders). Wolf Spiders carry their spherical egg sacs slung from the spinnerets. When the young hatch they climb onto the mother's back, clinging to special knob-shaped hairs. The mother carries them about until they moult and disperse.
In many species, like orb weavers, the egg sacs are simply abandoned, sometimes protected among leaves or in silk barriers, or even shallowly buried in soil (Nephila pilipes). Exposed egg sacs usually have a surface silk layer of dull brown, green or russet coloured silk, often further camouflaged with leaf debris to help prevent eggs being eaten or parasitised.
Huntsman Spider (Isopeda) clasping its egg sac. Photo: M Gray © Australian Museum.
Egg sacs
A. Opened egg sac of a Badge Huntsman Spider (Neosparassus sp.)
B. Characteristic egg sacs of the Magnificent Spider (Ordgarius magnificus).
C. Female Net Casting Spider (Deinopis subrufa) making egg sac.
D. Egg sac of a St Andrew's Cross Spider (Argiope keyserlingi)
E. Female Austracantha (Gasteracantha) minax with egg sac.
Photos: A. Pavel German; B,C Mike Gray; D. Bill Rudman; E. Ramon Mascord.
