No, spiders are not invading India.

posted in: News | 3

When it comes to public relations, few animals have problems as severe as spiders. There are two kinds of confirmed medically significant species of spider in the US, the widows (genus Latrodectus) and the recluses (genus Loxoceles). Although diagnoses of widow bites are probably fairly accurate, there is a huge problem with the overdiagnosis of recluse bites. In fact it’s very common for brown recluse bites to be diagnosed in areas where they have never been found and those who live in houses infested with brown recluses generally don’t get bitten. In fact, if someone claims to have been bitten by a brown recluse I generally assume they’re mistaken unless they actually captured the spider and live in the area where brown recluses are found.

Furthermore, there are entire species which are thought to be medically significant without evidence they cause harm in humans. The hobo spider, Tegeneria argestis is a prime example of such a species. The spider is widely reported to be medically significant, yet the only human evidence for this comes from highly dubious case reports where there is either no evidence the spiders bit the people in question or where the spider was not collected from the site of the bite. In fact, a recent article in the Journal of Medical Entomology indicates the venom of this spider cannot break red blood cells (which are relatively weak), and that they are not able to transport bacteria like MRSA which could cause skin lesions. In short, relying on eyewitness identification of spiders without collected specimens can result in quite a few mistaken diagnosis when it comes to spider bites.

So imagine my surprise when I stumbled across this article from the Daily Mail claiming that spiders are rampaging through the town:

And scores more have been treated in hospital after the town was suddenly invaded by the poisonous eight-legged creatures last month, which have left residents living in a state of panic.

Now worried local officials are considering spraying the town with insecticide to kill off the menace, after experts have so far failed to identify the species.

A scientist, who is one of those now camping in the area in an attempt to tackle the dangerous spiders, described the creatures in question as ‘highly aggressive’.

Dr Saika, told the Times of India that the arachnid could even belong to a whole new species.

He said: ‘It leaps at anything that comes close. Some of the victims claimed the spider latched onto them after biting, and if that is so, it needs to be dealt with carefully.’

Rumours are rife that the spiders could be any of a number of poisonous arachnids, including possibly a tarantula, a black wishbone, or even the feared funnel-web spider.

Okay… so perhaps not surprised. Stuff like this is fairly routine, but let’s deconstruct the claims in the article for a moment.

  1. These spiders are highly aggressive and bite with incredible tenacity, even latching onto the victim. Yet, it appears nobody has been able to collect a specimen which actually bit a person and made them sick.
  2. Researchers are running tests to figure out ‘how toxic the spiders are’…yet nobody had been able to collect the spiders which bit them, and the doctors are apparrently relying on the accounts of the victims.
  3. Two of the three spiders listed in the article, the funnel web spider and the wishbone spider are native to Australia and are separated by an entire ocean. The third spider mentioned, the tarantula is actually a common name that refers to a very common family of spiders (the Theraphosidae) with a worldwide distribution and which represents nearly a thousand species.

Even the stock photo is wrong. The picture showed in the article is Pterinopelma sazimai, a tarantula species described this year from Brazil.

*sigh*

I’m not familiar with the fauna of India (although I have kept Indian tarantulas as pets), but here’s my guess at what’s happening. Here in the US, we occasionally get huge blooms of spiders in incredible densities. The spiders I generally see associated with these webs are spiders of the genus Tetragnatha, but Anelosimus species also commonly do this. In fact sociality is surprisingly common in the spider world, and most of the species that engage in this behavior are completely harmless.

What probably happened is that a bloom of these spiders occurred during a time of year when many people would notice them. Somebody got a wound that got infected, got it improperly treated by a local witchdoctor (the Indian equivalent of a Naturopath) and allowed the infection to spread out of control. The witchdoctor blamed it on a spider bite to avoid blame for themselves, the victim repeated this to medical professionals and the medical professionals took this at face value. After this, the media got ahold of the story and allowed it to get out of control and fester.

In fact, Dr. Saikia has gone on record and cleared up what happened. From a June 4 article on CNN:

Last month, LR Saikia and a team of researchers from Dibrugarh University visited the town to investigate what had happened. Saikia told CNN that he believed the man may have died from a snake bite, while the boy may not have suffered any bite at all.

“The evidence that we gathered does not support the claim that they died after being bitten by spiders,” Saikia said. Saikia added that the man’s relatives appeared to have taken him to traditional spiritual healers instead of qualified doctors when symptoms appeared. He confirmed that about 12 people have visited hospitals in the area recently, complaining of spider bites.

“Only two of them were confirmed bitten by spiders. But they were ordinary spiders,” Saikia said. Investigators drew their conclusions from questioning relatives of the two dead people about the type of bite marks and symptoms, Saikia said. Some 20 spiders resembling tarantulas from the incident were handed over to investigators during their week-long stay. Tarantulas indigenous to the region are not known to be fatally venomous, but about five of the recovered spiders are currently undergoing tests.

When asked if spiders were likely to have swarmed the town of just under 1,000 people, Saikia said, “This is just a story … based on rumors.”

So misdiagnosis of spider bites isn’t just a problem in the US.

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Joe Ballenger is an entomologist who works in the biotech industry as a contractor. In his spare time, he helps answer questions about bugs at Ask an Entomologist. https://askentomologists.wordpress.com/