Red Back Spider infestation across Mt Evelyn

Climatic conditions particularly at the start of March as well as extremely humid to wet conditions in February have led to an intense infestation of Red Back Spiders (Therididae- Latrodectus hasseltii) in many areas but especially Mount Evelyn.

MEEPPA in conjunction with the Chamber of Commerce and several business owners/managers requested urgent assistance from the Yarra Ranges Council in having the infestation treated in a quick and timely manner within the CBD which has now been completed but we know that this is just the tip of the iceberg and that many households across the area of the township will have a similar problem.

Redback Spider spraying
Red Back Spider infestation treated in Mt Evelyn’s shopping precinct early last week.
Photo by Greg Carrick

Red Back Spiders are generally docile and one of their best known Defence Mechanisms is to fall off their webs and pretend to be dead with their legs curled up. However at this time of the year they will have anywhere up to 5 or more egg sacs – white in colour and about the size of a pea usually suspended high in the messy web which is always attached to the ground with viscous (very sticky) webs which will also pick up leaves and other ground debris carried in the wind. Around building perimeters low sticky webs with leaves and small sticks/bark suspended is usually a good preliminary indication that your house/outbuildings might be infested.

The spiders usually have a retreat on top of the web or will be sitting upside down across the egg sacs which makes them much more active, aggressive and fast moving especially on warm humid nights. It is Only the Females who are the classic ‘Red Backs’ with a Red Stripe on the top of the abdomen and a red ‘hourglass’ underneath. The males are tiny in comparison and are no threat. Due to the fact that the Females can store sperm and eggs between moults (every 12/18 months) the males are usually absent due to being eaten. In the U.S. that is why they are called ‘Black Widows’ but is common in many spider families.

Favourite haunts around buildings and the yard include:
Below Window Sills – brick, wood or even newer aluminium. Plants hanging over retaining walls but with web usually in contact with the ground. Corner of Door Frames. Gas Meters as well as Electrical Boxes on side walls. Corners of verandas. Sleep Outs. Patios and especially under Patio Furniture as well as Plastic chairs

Inside under sinks as well as overlapping cupboards in bathrooms – especially if the weather changes dramatically outside. They will enter houses and will seek damper places below dry retreats.

Around the Garden:
All Pool equipment – especially pump housings. Garden Hose Reels. Woodsheds/stacks. Stacks of iron, timber – almost anything stacked but especially stacked flower pots plastic or otherwise with drainage holes. Old cans, tins and general rubbish including cardboard boxes left in sheds. Any can of mower fuel left on a shed floor for any length of time. Open Carports. Folded Tarpaulins or tarps which have been left over anything in the yard for more than a few weeks. Any smaller garden sheds or building which have ridged profiles to ground level are a popular retreat. Old Cars and even Caravans. Be wary of your Rubbish Bin Lids and under the lip the lid falls onto.

Any Children’s toys in Sandpits, corners of sandpits interior or exterior, and especially Plastic Toys or Walker type ‘tractors and bikes for very young children which have even been left in the carport or on the lawn including Cubby Houses etc are also opportunistic places for them.

Also any moulded plastic play equipment especially under slides etc.

Confusing Related Species:
A spider in the same family is the ‘Black or Brown Cupboard or ‘False Widow’ Spider’ (Steatoda Grossa) which looks exactly the same and is capable of a very painful bite but no where as toxic as the Red Back is also very common in the same locations.
It has all the same features EXCEPT that there is absolutely NO Red markings either on top or underneath.
Many reported ‘Red Back’ bites have been these offenders.

Spiders similar to the Red Back but not as toxic
Brown Widow and False Widow Spider. From the same family as Red Backs which can give painful bites but not life threatening.

If you believe you are bitten?
Red Back bites are serious and Medical Attention is essential. However the First Aid compression bandage method is of little use with these bites. Try to keep the specimen. No one has died from a Red Back bite for over 60 years now as an anti venom in severe cases is available but not always used. There is redness at the bite site and within an hour possibly a red radiating ‘ring’ visible. Above all keep the patient reassured and use an ice pack directly over the bite or a packet of frozen peas etc. You will have time to get to a hospital or medical centre. Later effects include Nausea, tightening of stomach and abdomen and almost Flu Like symptoms.

If the patient is a Child under 6 or a Senior over 65 ring for an ambulance immediately – particularly if they have any known cardiac, neurological or breathing problems.

None of us like using dusts and sprays around our houses and children’s play areas but if the infestation is too big to handle you might have no choice. Bifenthrin is used commercially as a spidercide as many insecticides containing just pyrethrins such as mortein are not as effective against Spiders who breathe through Book Lungs under their abdomens and not body pores like most insects.

Here are some other natural ideas:

Mt Evelyn Environment Protection and Progress Association

  1. I have a red back spider just inside roller door of garage with two egg sacks. I was just going to try to sweep her out in daylight hours with broom before sacs hatch, then squash sacs? Or would it be better to spray am not keen on it but worried about hundreds of baby red backs getting into house/car and cat or myself being bitten.

  2. Hello Belinda
    If the Spider is any larger than the size of a pea there will probably be others – check corners or any boxes or things stored touching ground or look in corners or under step if door connects to house(?)
    If you’re satisfied it’s only one you can remove it by getting a sturdy stick or piece of straight coat hanger twirling it through the web with the Eggs dropping it on the ground and squashing the Spider and the sacs with your foot – that’s called ‘Mechanical Removal’ – the Webs are very sticky
    The Spider may fall down and play dead anyway making it easier. I don’t usually advocate killing spiders but this is 1 of about 5 – I would ‘Mechanocally move ‘ and destroy especially if younger children around or elderly
    Do not use a Vaccum Cleaner unless it is up high in a corner or out of reach but b then open it OUTside and make sure the Spider is dead. EG Many people vacuum Huntsman but they can often survive being sucked up.
    Bifenthrin is available as a Spray or Dust at Bunnings – it’s also used for large Ants.

    1. Hi Franc,
      Thank you very much for your advice. I don’t like killing them either as have had this red back in garage for a while but was worried that hundreds of babies would be able to get into house as garage is accessible through laundry. Also neighbours garage door is right next to mine. I also found another one with 3 egg sacs some hatched just outside garage next to front balcony. I mechanically killed both spiders, eggs and as many babies as could see. Didn’t enjoy doing it but think it’s more humane method. I think there may be another female outside but not sure and can’t see any egg sacs. If I find any more with egg sacs may have to get the bifenthrin spray. Thanks for the tip.

  3. It sounds as if you may have more if they are near your balcony.
    Check areas between base of house and any plants touching the walls etc.
    At least with bifenthrin it is based on a more organic approach through pyrethrum from Chrysanthemum flowers – but its pretty deadly to fish so keep away from aquariums.

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