Rise of the false widow spider in Ireland
Our Irish shores have been invaded by a spider with a venomous bite that’s 230 times more potent than that of our native species. That’s alarming news for Ireland as we’ve been blessed by the absence of such creatures since the days of Saint Patrick. Our mild and temperate climate has never been too favourable to settlers of the venomous kind. But now, due to climate change and the invading arachnid’s impressive array of natural advantages, it thrives and is here to stay.
The false widow spider is quickly becoming the dominant species found in many cities and counties around the country. Since first appearing in 1999, they are already the most commonly found spider in Dublin’s suburbs. And with a bite that can land you in hospital, the growing concern with their increasing appearance is warranted.
The unfortunate news of a 15-week-old baby being bitten multiple times in Cork and getting rushed to hospital by a traumatised mother is enough to grab our media’s attention and to raise national concern.
Encounters with the false widow in Ireland will spike this autumn as the temperature drops and they find their way into our homes for warmth. This in turn will mean more bites and, on rare occasions, more hospitalisations.
So what exactly is this invasive species and why are they thriving here? How dangerous is the false widow spider in Ireland?
The false widow spider in Ireland
The false widow spider was reportedly first seen in Ireland in Bray during the late 1990s. It is believed to have arrived with bananas imported from the Canary Islands. Since then, the spiders have established a strong foothold and are already thriving in most eastern counties. They’ve since spread to most counties and are a common sight now in Sligo and many major cities.
There are several species of spider that fall into the “false widow” category. The most commonly seen in Ireland are Steatoda nobilis, Steatoda grossa, and Steatoda bipunctata.
The Noble false widow spider (Steatoda nobilis) is the one catching the Irish headlines lately. In contrast to our native spiders, not only do they have a longer lifespan (up to five years), but they are more active during our colder seasons. This seasonal ‘leg up’ over our native spiders is then exploited in a numbers game, where the Noble false widow can produce up to one thousand offspring in a single year. These “invaders” can quickly disrupt the balance of a surrounding ecosystem, which means trouble for our native spiders. In a dramatically short period of time, they’ve been outnumbered by the invaders and outgunned by the potency of their bite.
The Noble false widow can easily bully native spiders out of their habitats, brushing them aside to claim the prime real estate. A warming climate then accentuates these advantages as it begins to resemble its native home temperatures. They’ve settled in nicely.
What does a false widow spider look like?
While they closely resemble the black widow in appearance and characteristics, the false widow tends to be more brown in colour with reddish-orange legs. Some may be a very dark brown in colour, nearing black. Adults tend to have large and shiny bulbous abdomens with a white or cream coloured band around its front, near the spider’s head. Other light coloured markings are often present but these patterns will vary by species.
In the Noble false widow, the abdominal markings are often described as resembling a skull (just a skull shape, no crossbones). In rare cases, an adult female without markings may be dark enough to make it near indistinguishable from the black widow. However, the black widow has a clearly defined red hourglass shape underneath its abdomen. We do not recommend flipping them over to ‘investigate’ in times of doubt. Black widow imports are extremely rare in Ireland.
Between the sexes, female false widows have a larger and more globular, shiny abdomen than the males. Generally males are smaller and less rounded in shape, but their markings are often more clearly defined. Female Noble false widow spiders average in size from 9.5 to 14mm, while males are usually between 7 to 11mm. The larger female specimens can span about the size of a two euro coin. Very young male and female false widows are indistinguishable and they can often be seen floating on thin strands of web as they descend from trees and bushes.
Where will I find a false widow spider?
The false widow spiders in Ireland are generally found in and around houses and other built-up areas. They prefer elevated positions such as the top corners of rooms, sheds, rafters and garages. During colder months they will venture inside to the warmth of our living areas, conservatories, kitchens and bedrooms. So unfortunately, the chances of finding a false widow spider in your home will increase dramatically this autumn. It’s been reported that 88% of false widow bites in Ireland occur under bed sheets and in clothing.
Outside, they are often found around window frames, wall crevices, gutters, and in trees. During the day, it’s common to see their legs poking out from a hole or crevice containing a web. The spiders are usually more active at night and the female Noble false widow is usually seen waiting upside down in her web. Adult false widow spider webs are often an unstructured and messy tangle of very strong threads. If the web is a prime location and left alone to develop, they may become very dense with well rounded entrance funnels.
How dangerous is the false widow spider?
A recent study by NUI Galway (NUIG) shows that the venom of a Noble false widow spider is 230 times more potent than that of native Irish species. Containing two thirds the venom of the Black widow spider, the false widow spider bite packs a serious punch that has recently been deemed as ‘medically significant’. The study indicated that the Noble false widows can judge and interpret the likelihood of success when attacking its prey by measuring the amount of remaining venom left in its glands. If there is little venom remaining, the spider instinctively targets smaller prey so as to not risk injury or even death.
The study went on to note that in the process of attack, the spider can accurately target the most vulnerable body parts of its prey, where its delivery and uptake of the venom will be most effective. This helped the scientists to determine that its methods are not random, and remarkably the Noble false widow spider had a resulting 95% success rate when attacking its prey. The results from this study suggest that the Noble false widow population will continue to grow around the country.
A false widow spider bite is not fatal and thankfully, the majority of their bites are produce only mild symptoms. The false widow is not aggressive and will usually only bite a person when it feels threatened. Its preferred option is to flee towards safety, usually to the most sheltered portion of its web. Their venom is a precious resource that takes time to generate and so they will use it very sparingly. “Dry biting” is when the spider bites without releasing any venom through its fangs. This appears to be its preferred mode of defence against an unintentional assailant as big as a person. As their fangs often contain harmful bacteria that are highly resistant to antibiotics, even a dry bite can cause severe problems if ignored.
- Mild Pain
- Debilitating pain
- Impaired mobility
- Allergic reaction
- Tissue necrosis
- Severe bacterial infection
How to treat a false widow bite
- Don’t panic. Clean the wound by washing the area with soap and water.
- Apply an ice pack or a clothed cooled in water for 10 minutes and elevate the wound.
- Cover the bite area with a bandage to help prevent infection. Avoid scratching the bite area
Seek urgent medical advice if vomiting, radiating pain and/or hot/cold flushes develop and for bites on or around the eye.
Contact the NPIC, GP or pharmacist if pain persists or swelling develops.
How to avoid a false widow bite
The following tips might save you from an unpleasant encounter.
- Close windows in the evening. This is when the spiders become more active and will try to enter your house for warmth.
- Removing spider webs around the home and cleaning regularly will discourage them from wanting to stay inside.
- Avoid leaving clothes on the floor where they are easily accessible to the spider.
- Wear gloves when working outside or in sheds. Consider storing them somewhere where the spiders can not crawl into them.
- Keep your wheelie bin handles and lids free of their webs.
- Fumigating your home will likely only work in the short term, as the spiders will simply return when it clears.
- Peppermint or tea tree oil solution sprays have been successful as a deterrent.
The false widow spider is something to be aware of but not feared. They are not aggressive and will only bite a person if it feels threatened. They don’t like to be squashed, but unfortunately that’s what they experience when we accidentally roll over them or trap them against our skin when getting dressed. This is when they bite. So there’s some added motivation in keeping a tidier room and our clothes up off the floor at least. But they are not out to get us and they will avoid direct human contact when possible.