Many people can identify the common spiders in Australia, but do you know what the different species do with their eggs? They generally build an egg sac, which they either carry or hide.
Spider Eggs and Egg Sacs
The shape, size, colour and placement of a spider’s egg sac depends on the species that laid it. Some spiders can control the colour of the silk that surrounds the eggs, to better camouflage them from predators and parasites. However, in many species the mother is more personally involved in their safety, either carrying the egg case or standing on guard nearby.
Egg sacs of common Australian spiders
Redback spiders (Latrodectus hasselti)
Redbacks lay four to ten smooth round egg sacs that resemble polystyrene beads, suspended in the web. They are white or sometimes yellowish, and each can contain 250 eggs.
Cupboard spiders (Steatoda grossa)
Like the redback, cupboard spiders also lay round egg sacs, but the outer layer of silk is fuzzy rather than smooth. Well-fed females lay three or four sacs a year, with 40 to 100 eggs in each.
Daddy-long-legs (Pholcus phalangioides)
Daddy-long-legs only produce 13-60 eggs, bundled in very thin silk, and resemble a pinkish-white blackberry held in the spider’s jaws.
Huntsman spiders (Family Sparassidae)
Huntsman spin a flat, oval egg sac of white papery silk, containing up to 200 eggs. She will then place it under bark or somewhere with similar concealment, and stand guard over it until they hatch.
White tail spiders (Lampona spp.)
White tails spin a silk retreat with an oval egg sac inside it, containing 80-100 pink eggs, and like huntsmen spiders, the female will stand guard over it.
Wolf spiders (Lycosidae)
Wolf spiders carry their white, oval egg sac in their jaws, and become very agitated if separated from it.
The largest spider egg sacs you are likely to encounter are those of the magnificent spider (Ordgarius spp.). These garden spiders spin up to seven spindle-shaped brown silk egg sacs, each 8cm long, containing 600 eggs, hung from branches like Christmas ornaments. They are easily mistaken for the cocoons of a large moth.
How long do spider eggs take to hatch?
If they avoid predators or parasites, the eggs hatch in weeks to months, depending on species.
The young spiders which hatch are called spiderlings. Often they will disperse immediately after hatching. The spiderlings of many species disperse by ‘ballooning’ – they spin a long strand of silk from a vantage point above the ground and use the wind to carry them away. In some species such as the wolf spider, the spiderlings will stay with their mother, riding on her back until after the first moult.
Getting rid of spider egg sacs
A spider spray to take care of the adults won’t always kill eggs inside the sac due to the waterproof nature of the silk. However, the spiderlings will generally die on hatching. But to be sure, if you see a spider egg sac, it is best to physically destroy the egg sac (stamping on it works well!). However, make sure the mother is dead, as she will often be very aggressive in protecting her eggs.
Daniel Heald, technician and entomologist