Monday, 20 August 2012

Like fire-walking over flaming charcoal with a 3-inch rusty nail grinding into your heel

As probably you know, the sting of a wasp is more painful than the the bite of a mosquito (though not necessarily more dangerous!). If you wanted, you could rank the stings of all insects in order, from the mildest to the most painful, but don´t worry, you don´t have to, for the Hymenoptera (bees, wasps and ants) it has already been done - the Schmidt Pain Index.

So who is the winner?, the most painful possible sting, described as......

"immediate, excruciating pain and numbness to pencil-point pressure, as well as trembling in the form of a totally uncontrollable urge to shake the affected part"
"Pure, intense, brilliant pain. Like fire-walking over flaming charcoal with a 3-inch rusty nail grinding into your heel."

Not a wasp, but an ant, the Bullet ant (Paraponera clavata), and guess where they live? Yes, as well as piranhas, anacondas and parasites that enter your private parts when swimming, Brazil also has Bullet ants! Mainly in the Amazon, but they´ve also been reported in the Cerrado, the hot dry savanna in the north of Brazil.

The Life of Bullet ants

Paraponera clavata (Wikipiedia)

Bullet ants live in colonies several hundred strong, mostly built in the soil at the base of trees, and ruled by a queen. And they are big, about an inch long, and jet black. Although they are omnivorous, and will chop up any insects they come across, their main food seems to be nectar, each day they climb up into the forest canopy and bring back nectar from the flowers there. But don´t imagine gentle giants, colonies can be quite close to each other and a state of war is more or less continuous. Injured ants give off a scent which attracts parasitic wasps, sort of ant Valkyries, who feed off the ants and lay their eggs there.

There aren´t many other things which eat Bullet ants, not surprisingly. But why exactly is the venom so powerful.

Why so painful?

Bullet ants sting through a syringe-like spike at the tip of their abdomen. The consequent horrendous pain can last until the next day, and meanwhile you will have nausea, trembling and probably paralysis. It takes a lot of stings to actually kill you, about 30 per Kg of your weight, though after just one, death probably feels like a good alternative

Like most venoms, the Bullet ant sting is a cocktail of bad things, but most of the effect comes from poneratoxin. This blocks nerve transmission and causes long lasting contraction of smooth muscle fibres, which translates as pain and trembling. One sting contains only 1 ug of poneratoxin, a tiny, tiny, quantity, but enough.

What are they good for?

Various Indian tribes of the Amazon have utilised Bullet ants for years. The sting is a treatment for rheumatism, presumably as the pain takes your mind of it. More productively, the mandibles at the other end can be used as a form of suture, they clamp shut on a wound even when the head of the ant is twisted off, and ant saliva causes the patients wound to swell, closing it.

The Satere-Mawe tribe have found another use. Hundreds of ants are sedated and then woven into a leaf to form a sort of glove. Wearing this glove for 10 minutes, and surviving, is an initiation rite for boys of the tribe. The Satere-Mawe were also the first people to domesticate the stimulant producing Guarana plant (Paullinia cupana), the product of which is now found in a hugely popular soft drink in Brazil. All of which suggests that the Satere-Mawe have a rather "innovative" approach to biology.


A very good guide to poneratoxin by Vivienne Baillie Gerritsen can be found at

Friday, 17 August 2012

Pity the poor mosquito!

You are probably, dear reader, a little prejudiced against mosquitoes. Take Aedes scapularis. Whilst it´s true that it is a vector for yellow fever, and  human and Venezuelan equine encephalitis, poor A. scapularis has a hard life. In 2002, Casanova and do Prado studied them in the pastureland around a farm near Campinas, in Sao Paulo state, Brazil.

During the hot rainy season (October to March) muddy puddles form all over the land, and the drought resistant eggs of Aedes scapularis hatch, little larvae swimming off hopefully into the water. It seems a good life in a hot bath full of rich organic matter, but little scapularis does not realise the horrors ahead.

For a start, it might rain, it might not, it might rain a LOT. Aedes only needs 9 days from hatching to adulthood, but even that might be too long. Of the 58 populations studied by Casanova and do Prado, 27 were wiped out by their ponds drying up, and 15 were washed away by floods, they never stood a chance.

Life in the 16 remaining pools was better, but not by much. The good news was that starvation was almost unknown, the bad news that all those mosquitoes ensured that starvation was unknown for their predators too. Estimates of total mortality from tiny larvae to emerging adults varied from 68 to a massive 96% per pool!

Predators included........

Giant water bugs "Baratas d' aqua" (Belostomatidae), aggressively predaceous insects who feed on, well, anything, injecting a digestive saliva and sucking out the remains. One of the most painful bites of any insects to us, let alone to a little mosquito.

Giant Water Bug larva (Wikipedia)

Water scorpions (Nepidae) - actually another type of insect

Diving beetles (Dytiscidae) -  you can eat these, if you want to,  in Mexico the adults are roasted and salted and added to tacos

Dragonfly larvae - there are, incredibly, at least 267 species of dragon- and damsel-fly in Sao Paulo state alone, and many of these eat mosquitoes

Last, but not least, larvae of a predatory mosquito, Psorophora ciliata. Don´t start to feel too grateful to this one, they feed on us as well, and infact are the largest blood feeding species found in the USA.

So, the little larva hatching into a warm, muddy, pool will almost certainly desiccate, be swept away, or be eaten. No wonder they are so angry!

Key-factor analysis of immature stages of Aedes scapularis (Diptera: Culicidae) populations in southeastern Brazil byC. Casanova and A.P. do Prado (Bull. Entomol. Res. 92, 271-7)