Getting Rid of Redbacks

Controlling the resilient Redback

The Redback has successfully established itself in Australia. It is a hardy spider than can withstand high temperatures and prolonged dry periods. It is completely indiscriminate about where it builds its web. And it constructs a deep retreat to maintain its security.

How, then, can the Redback be controlled?

Spraying with insecticides is one possibility. However, like all spiders, the Redback can close off its lung openings and exist for several hours using very little air. Hence, a spray must be very long lasting, or used in such volumes that the spider and all of its surroundings are drenched. Surface-acting sprays seem to work reasonably well.

The shape of the web also limits the effectiveness of sprays. The Redback's web is thimble- or bucket-shaped, with the opening pointed towards the ground. Sprays are typically delivered from positions higher than the nest and may not actually affect the spider high up in the nest. Equally, the silk of the egg sac is impervious to such lightly delivered sprays and the young continue to develop within the sac.

However, even if a 'total kill' is achieved, spraying must be repeated frequently as one decent breeze can carry in a new batch of young spiders that can quickly recolonise a 'clear' area. To be totally effective, every house in an entire suburb would have to be sprayed, both inside and out.

The problem with using insecticides is that they are indiscriminate, killing all spiders, even the harmless ones that help to control Redbacks and insects. Thus, spraying has only a temporary effect on the Redback Spiders, but may have a devastating effect on the populations of all spiders, including the natural predators of the Redback.

Reducing Redback numbers

In our experience, the most effective method of Redback Spider control could be termed 'informed vigilance'. First, take careful note of the web in which you found the Redback. Notice that it is fine but strong, with an obvious outer portion and a hidden inner portion in which the spider hides. Usually, the web is strong enough to hold dead leaves and twigs blown into it. Note the location of the web. Take a stick or small brush. Push it quickly back into the web as far as it will go, and roll the spider, its eggs and web onto the stick. Remove and crush the spiders and eggs.

Now search other likely locations for similar webs, beginning near the first web site. Always be sure to check the garage and driveway - adult Redbacks are frequently transported in the bodywork of cars.

The curiosity of children is often aroused when they see webs and spiders. If young children are in the area, it is important to pay careful attention to low ledges. These are best seen by getting down close to the ground and looking up.

Once an area has been thoroughly checked, and the spiders and egg sacs destroyed, a weekly casual check and eradication will substantially reduce the numbers of young Redbacks establishing themselves.

Redbacks are most vulnerable in the cool, dry winter. Insect food is scarce and the spider is forced to live on available reserves. Redbacks appear to survive the winter only in areas of sufficient sunlight and warmth. Follow the sun and look for areas that are heated throughout the winter's day or a good part of it. These are likely sites, as Redbacks need to stay warm and dry.

Wind and rain at the onset of winter can substantially reduce Redback numbers. Equally, early onset of summer heat and dry conditions will allow early mating and extra generations. A sustained attack on Redbacks during the winter will ensure a much quieter spring and summer to follow.

Natural enemies of the Redback

The most formidable natural enemies of the Redback Spider appear to be other spiders, including those of the same family, the Comb-footed Spiders. Redback Spiders have been captured and consumed in the web of the Black House Spider and of the Daddy-long-legs.

The Black House Spider is native to Australia and its presence seems to be a noticeable deterrent to Redback invasion of houses. The Black House Spider occupies untidy lacy webs that 'decorate' eaves, verandahs and window sills. It builds its web in similar areas to those used by the Redback. Often houses that are covered with the Black House Spider are free or almost free of Redbacks.