Adult tarantula hawk on a plant

Tarantula hawks have a sinister secret © Ian Norman Via Wikimedia Commons

The most painful wasp sting in the world explained

Armed with one of the most painful stings on the planet, tarantula hawks are a spider's worst nightmare.

A fear of insects is common among humans, but for some spiders, stings really can be a matter of life or death. One wasp in particular makes even the biggest, hairiest spider run away in terror: the tarantula hawk.

Dr Gavin Broad, wasp expert at the Museum, uncovers the eccentricities of this small but sinister creature.

Bird or spider?

Despite their name, tarantula hawks (Pepsis genus) are actually a species of spider wasp.

Pepsis heros

The largest species of tarantula hawk, Pepsis heros, will be going on display at the Museum in summer 2017

 

Reaching up to 11 centimetres in length, these insects lead solitary lives and their 133 known species are found across South and Central America and in the southern United States.

They are named after their habit of hunting tarantulas, which are often considerably larger than themselves - but these wasps do so with little risk to their own lives.

'The wasps always win. I don't think anyone has ever seen a tarantula kill the wasp,' says Gavin.

'The spiders will usually try to flee or avoid them at all costs.'

Frozen dinners

Adult tarantula hawks get their nutrition from nectar, but only the females will battle spiders to provide food for their offspring.

They pierce the tarantula with a sharp, curved sting, rapidly injecting venom that permanently paralyses but keeps its hairy adversary alive.

A female tarantula hawk's sting

A female tarantula hawk's sting can be up to seven millimetres long © Rankin1958 Via Wikimedia Commons

 

The incapacitated spider is either held captive in its own burrow or dragged to the wasp's nest. The female then lays a single egg on the spider's body.

The purpose of this act: a pre-prepared dinner.

When the egg hatches, the larva burrows its way inside the spider's abdomen and begins feasting on the still-living tarantula.

It begins by feeding on haemolymph - the spider equivalent of blood - before gorging itself on the tissue.

Eventually the offspring emerges from the spider as an adult tarantula hawk.

Gavin explains, 'The spider has got no chance. Even if you took the larva away, it wouldn't recover.'

'It would remain in a state of suspended animation for quite a while, until eventually its respiration would stop.'

Wasp drags paralysed tarantula

Once it has stung, the wasp drags the paralysed tarantula back to its nest to be a host for its larva © Alan Schmierer Via Wikimedia Commons

 

If stung, just scream

For humans and other vertebrates, the tarantula hawk has one of the most painful stings on the planet.

American entomologist Justin Schmidt created the sting pain index, with the help of variably willing or unwitting test subjects. He once described the tarantula hawk's sting as 'instantaneous, electrifying and totally debilitating'.

The tarantula hawk has been awarded second place on the Schmidt sting pain index, beaten only by the South American bullet ant (Paraponera clavata).

The pain from a bullet ant sting lasts up to 24 hours, whereas that of a wasp usually only aggravates the unlucky victim for five minutes.

Schmidt has also in the past suggested that when stung, the only response is to 'lay down and scream'.

Bullet ant

The bullet ant is the only insect with a more painful sting than the tarantula hawk © Graham Wise Via Wikimedia Commons

 

'In Schmidt's ranking of one to four, he tries to be objective, so each category is quite broad,' says Gavin. 'Number two is broadly comparable to a honey bee.'

The tarantula hawk earned a top score of four, making its sting almost unbearably painful.

Champion defender

Tarantula hawks are fairly docile unless provoked, although the threat of debilitating pain appears to have left this insect mostly unchallenged, with no known predators.

Some species have wings in an intense shade of bright orange, a typical danger sign to would-be predators.

Stinging is the wasp's main defence. The insect's hard, smooth exoskeleton and legs covered in sharp spines act as defensive armour, protecting the wasp long enough to inject its venom.

While spiders are left paralysed by the venom, for vertebrates (such as humans) it causes extreme pain. It is a distraction big enough to give the wasp a chance to get away to safety.

Tarantula hawk feeding on pollen

Adult tarantula hawks are pollen feeders. Only their offspring are carnivores. © Davehood Via Wikimedia Commons

 

Witness the swarm

Visitors to the Museum can see the largest species of tarantula hawk, Pepsis heros, from southeastern Peru in the recently redeveloped Hintze Hall. The specimen is part of an impressive new display of swarming insects.

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