Brown Widow spiders on Raro

Monday June 30, 2014 Written by Gerald McCormack Published in Weekend
North American specimens of Brown Widow showing the totally dark form and the typical form. It also shows the spiky egg cases that are very different from the smooth, non-spiky egg cases of the Black Widows and Redback. 14062538 North American specimens of Brown Widow showing the totally dark form and the typical form. It also shows the spiky egg cases that are very different from the smooth, non-spiky egg cases of the Black Widows and Redback. 14062538

Natural Heritage Trust Director Gerald McCormack has made a full study of the recent spider infestation that has caused both concern and angst on the island.

People have wondered why they took so long to be discovered on Rarotonga, as well as how they were allowed to get into the country in the first place.

Rarotonga Freight Services (RFS) staff had seen unusual dark spiders in their warehouse and on the evening of May 20 they caught one, and gave it to Biosecurity the next morning. The spider was completely dark except for a reddish patch under the abdomen. The lack of red on the upperside of the abdomen ruled out the Australian Redback and entomologist Dr Maja Poeschko concluded that it was probably a black widow and sent the specimen to New Zealand for confirmation.  On the 24th the Cook Islands News announced the discovery with a dramatic image on the front page of a Black Widow, and the story on page seven included two images of the local specimen.

Poeschko arranged for pest controller Henry Wichman to spray the contaminated site and surrounding area, and Biosecurity staff started tracking containers and checking for new contaminated sites.

On May 26 they found a second site in an airport warehouse 800m west of the first site and linked to it by containers that arrived on Rarotonga on December 8. The site was severely contaminated and appeared to have been infected before the first site.

On the 29th Wichman found a third contaminated area at Timberland near RFS, and this led to the fourth site on the 31st at Timberland in Arorangi, three kilometres from the airport.

On the June 8, Air Rarotonga staff found spiders in the hangar, and Wichman started a spraying programme which led to spiders also being found in the Air Rarotonga cargo shed and upholstery workshop. Biosecurity started turning up new sites with depressing regularity: Motor Centre in Panama, CITC Supermarket and Hardware in Avatiu, Michigan Motors in Taputapuatea, and Pickering Motors in Tutakimoa. As each site was located, extensive spraying was undertaken.

On 16th June I was given an Air Rarotonga specimen and identified it as a Brown Widow. After discussions with Maja, we concluded that there were probably two species present, a black widow and the Brown Widow.

We started back-checking on egg cases and found the spiked egg cases of Brown Widow at all sites except RFS and the adjacent Timberland where they were reported to be smooth, indicative of a black widow.

On June 17 the Ministry of Agriculture issued its May “Field Report” about the black widow. The report was illustrated with internet images of black widows. It also included an image of a pale brown spider from Air Rarotonga, noting that it might be a Brown Widow and that it would be sent to New Zealand for confirmation. Agriculture also issued a “Biosecurity Public Awareness” sheet with internet images of black widow spiders.

On June 19 the situation simplified when New Zealand scientists reported that a DNA analysis proved beyond doubt that the spider from RFS was a Brown Widow, even if it was an atypically black specimen. It just shows that a widow which is black is not necessarily a black widow - it can be a black Brown Widow. The purported smooth egg cases could not be verified from any of the many collected samples.

The widow spiders

There are at least 30 species of widow spider in the world, all in the genus Latrodectus. Americans use the name “black widow” for three of their four native widow spiders: the Southern Black Widow, the Western Black Widow and the Northern Black Widow. The name arose around 1900 in the US combining the widows’ colour with the belief that she widowed herself by eating the male after mating, which is now known to be very rare among American “black widows” in the wild.

Widow spiders are native in most countries including Australia and New Zealand but not on any Pacific Islands countries. The native Redback (Latrodectus hasseltii) of Australia and Indonesia and the Katipo (Latrodectus katipo) of New Zealand are very closely related to the four North American black widows.

Most widows spread slowly and naturally to adjacent areas that are suitable; this area is known as their native range. The exception to the rule of natural spread is the hitchhiking Brown Widow or Brown Button Spider (Latrodectus geometricus), which originated in Southern Africa. This spider has spread along human transport systems to become circumtropical and subtropical, including India, Australia (pre-1953, near Sydney), Indonesia, PNG, Philippines, Japan, and Hawai’i (pre-1939). In the Americas it is widespread in South America, the Caribbean islands, and Florida (since 1935) and recently across the southern states from North Carolina to California (pre-2003, Los Angeles). In the South Pacific it in Tahiti (2012).

Like the Brown Widow, the Australian Redback is common in urban areas and hitchhikes on vehicles and cargo. Overseas it established a couple of colonies in New Zealand in the early 1980s - also in Japan, Iran, and United Arab Emirates. It is obviously a popular Australian export and, in June 2007, a female on two mature egg cases was intercepted on Rarotonga.

Although the widows of North America are reluctant hitchhikers, two species have established themselves overseas: the Southern Black Widow is in Hawai’i (pre-1925) and Australia (pre-1953); while the Western Black Widow is also in Hawai’i (pre-1981). Southern and Western Black Widows and Brown Widows have been found several times in New Zealand on table grapes from California.

Arrival on Rarotonga?

At one of the three most contaminated local sites, an Australian familiar with the Redback noticed that similar webs were common when he started work in April 2011. They were of no special interest to one who had experienced little discomfort from two Redback encounters in Australia. The level of contamination suggested that the spider had been present since about early 2009. It will now be very difficult for Biosecurity to track the details of the arrival of the spider five years ago.

The port of origin might have been Sydney, Honolulu or Los Angeles. Tahiti is not likely with Brown Widows found on the eastern side in 2012 and judged as “very recently introduced”. Our other Pacific neighbours are not known to have Brown Widow, and neither does New Zealand or China.

Brown Widow identification

On Rarotonga we have a few small native spiders in the same family as the widows, the family Theridiidae, the “tangle-web spiders”. Like the widows, they have glossy bulbous abdomens, make irregular three-dimensional tangle-webs in secluded places and have spherical egg cases. They are harmless for people.

Without inspecting the adult spider, the Brown Widow egg case is very distinctive, being a sphere about 5mm diameter covered with short silky spikes like an old-fashioned sea-mine.

The spider’s body is up to 10mm (excluding the legs) and the bulbous abdomen is typically mottled brown or tan with fine whitish markings and black spots, with an orange, yellow or red hourglass on the underside; its legs are pale with dramatic wide black bands at the joints. The body colour is variable, from pale brown with contrasting markings to dark brown with indistinct markings, although the legs are typically pale with black bands. And rarely, specimens are black bodied with black legs like the first one found on Rarotonga at RFS.

In contrast, the Southern and Western Black Widows of the States are distinctly larger at 15mm body length with totally black legs and body except for a vivid red hourglass under the abdomen; their egg cases are 10mm spheres with a smooth surface.

The male Brown Widow is tiny and harmless. He is also short-lived. He carefully courts the humongous predatory female and, if accepted, he starts mating. Suddenly he flips-about to put his abdomen near her mouth and she injects digestive enzymes and starts drinking his dissolving interior, while he completes his task.

When he has finished, alas, she continues drinking until he is no more or, if not so hungry, she wraps him live in silk to drink later. This self-sacrificing male behaviour is known in only one other spider, the Australian Redback. Although the personal price is high, this behaviour ensures that he is the father of most of her children.

Habitat, dispersal and control

The Brown Widow has an affinity for urban areas, which make human encounters more frequent. They live under objects, both outside and in storage areas, and on buildings around windows or in sheltered places. Check carefully before putting your hands into holes and under objects.

Its association with human structures, including vehicles, facilitates its dispersal along human transport pathways.

It is a prolific breeder with about 150 eggs per egg-case and it can produce 20 egg cases in a lifetime of two or three years. After the eggs hatch the spiderlings leave the egg case, and often prey on their brothers and sisters. The spiderlings usually walk to new nearby locations; but they can also climb on objects and exude a silk thread by which they “balloon” on the wind to more distant locations.

On Rarotonga most spiders have been in warehouses and buildings along transport pathways. With luck the spiderlings have found plenty of new sites within the buildings of their birth and none have walked outside to “balloon”. If this is the case, there is a good chance they can be eradicated by an intensive spraying programme.

If you find any Brown Widows please report them to Biosecurity.

You can also kill widows outright with “fast knockdown” pyrethroid fly-sprays. Removing the webs with broom or vacuum cleaner, and the use of a residual insecticide will discourage them from re-nesting in the same place.

Female Brown Widow bite

The Brown Widow rarely bites because she is timid and retires when disturbed, and when she bites she injects only a minor amount of venom. Whether this is because she has less venom or cannot inject it effectively is unknown.

A typical Brown Widow bite gives a sharp localised pain and leaves a red mark. Over the next hour or two the pain can become more extensive. However, a study of 15 verified bites in Africa showed that victims never developed the extreme pain, muscle cramping, abdominal or back pain associated with Black Widow, Redback and Katipo bites.

The immediate application of a cold pack can reduce the localised pain but do not squeeze, suck, open or bandage the wound; don’t apply a tourniquet. Localised heat treatment is not effective. You should also drink plenty of water but no alcohol. Medical help should be sought for small children, the elderly and the infirmed - and for yourself if the pain is unacceptable.

There is no anti-venom for Brown Widow bites because it is not necessary.

Further information: Brown Widows have been recently spreading throughout the USA and there are many authoritative websites, such as:

https://cisr.ucr.edu/brown_widow_spider.html

http://sarasota.ifas.ufl.edu/IPM/BrownWidow.htm

http://www.texasinvasives.org/pest_database/detail.php?symbol=47

http://www.ocvcd.org/bulletins/BrownWidowSpider.pdf

http://en.wikipedia.org/wiki/Latrodectus_geometricus

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