Who, What, Why: What's the worst place to be bitten by a spider?

An Australian has been bitten by a venomous spider on the penis for a second time. Which part of the body do you most want to avoid getting bitten or stung, asks Jon Kelly.

To be bitten once on the penis is unfortunate. A second time and you'd wonder if you were cursed.

On Tuesday the 21-year-old tradesman, identified only as Jordan, was using a portable toilet on a Sydney building site when he was bitten by a redback spider. Again.

"I'm the most unlucky guy in the country at the moment," he lamented to the BBC. The redback's bite causes severe pain, sweating and nausea.

But was this the worst place he could have been bitten?

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From "both experience and thinking it through", its possible to identify the least desirable places to be bitten or stung by invertebrates like spiders, bees and wasps, says entomologist Prof Adam Hart of the University of Gloucestershire.

Firstly, fleshy parts of the body, where there's extra room to inject venom and greater capacity for swelling. Secondly, areas with a lot of nerve endings, which are more sensitive and therefore painful. Hart says he's been stung by insects on his scalp, and this was far less unpleasant than when he was stung on a fleshy part of his arm.

But if you were to rank by preference all the places you could be bitten, "right at the bottom would be the penis", Hart says. "Genitals are fleshy and have lots of nerve endings."

With larger venomous creatures like snakes, whose bites are far more deadly than those of spiders, it's better to be bitten in the extremities rather than in the middle of your body, where your vital organs are located. The Australian wildlife expert Steve Irwin was killed by a stingray barb to the chest.

But with spiders and other insects, most bites are localised. Unless you have an allergy, or are bitten or stung hundreds of times, it's very rare to be killed by an invertebrate's venom, Hart says.

Very little academic research has been conducted into which are the most painful parts of the body to be bitten or stung beyond the Schmidt Pain Index, compiled by entomologist Justin Schmidt, which offers a tasting notes-style index of the painfulness of different stings.

After a bee stung his testicles, however, Cornell University graduate student Michael Smith devised an experiment to establish which was the most painful part of the body to receive a sting - he inserted a bee's stinger into different parts of his own body and ranked the pain on a scale of one to 10.

The least painful locations, he found, were the upper arm, skull and tip of the middle toe, all of which averaged 2.3 on his scale. The most painful locations were the nostril (9.0), the upper lip (8.7) and the penis shaft (7.3).

So while Jordan may have been extremely unfortunate, he could have fared even worse had the spider reached his nasal cavities.

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