The sting

Before I get to posting about the giant water bug parental care behaviors, I thought I might make a small digression and talk about an encounter I had with an insect a few days ago.  Now, I apoligize in advance for this not-so-appealing photo, but this is what my foot currently looks like:

my foot

my foot

See the big red spot in the middle?  I got that from an insect!  Three days ago!  The ants that have taken over my house (you can read more about them in my ant post) have now apparently invaded my closet and one of them got into my shoe.  I never think to check my shoes before I put them on (stupid, really, considering where I live), and the ant wasn’t all that thrilled that I was apparently trying to smash it by putting my foot inside my shoe.  I wouldn’t have known it was even there except that I felt a few familiar, sharp stinging sensations on the top of my foot and ripped the shoe back off.  Sure enough, out wanders this one tiny little Brachymyrmex ant.  That’s right – that welt in the photo, which is about a half inch in diameter and both itchy and painful, was caused by a 2mm ant stinging me!

Today I thought I might talk about ants and the common misconception that the pains that people experience when they encounter ants are bites.  Lots of ants do bite, but they simply have big jaws (or not so big in the case of Brachymyrmex!) and all they can do with them is pinch.  Ant bites don’t involve venom (a poison that is used to subdue prey or deter a predator), so the pain from a bite is short lived.  At most you’ll get a nice little red spot that quickly goes away.  The real pain, and any long term swellings or other allergic reactions, come from ant stings, not bites.

Let’s think about how another insect we’re more familiar with, the honey bee, stings.  Honey bees are well known for their stinging, especially if their hives are disturbed, and even more especially if they are aggressive Africanized (or killer) bees.  Honey bees have a long, serrated stinger that they inject into the skin of whatever is disturbing them.  They have venom sacs at the base of their stingers which pump venom through the stinger into the animal being stung.  This venom causes a lot of pain.  However, honey bees are a bit of a special case.  Because they have the serrated stingers, the stingers tends to stay inside the victim.  It’s basically a one way system, like a fishhook or some cactus spines, in that the stinger can be inserted easily, but the serrations keep the stinger from being pulled back out.  The bees are usually unable to pull their stingers back out of their victims and the whole back end of the bee will often rip off with the stinger, eventually killing the bee.  (There are some great photos of bee stingers and stings on the Wikipedia article on bee stings!)  In honey bees, stinging is effectively a suicidal action – most honey bees that sting do not live to sting again.  However, leaving the stinger behind is also an excellent deterrent.  Until the stinger is pulled out or runs out of venom, it is able to keep pumping painful chemicals into the victim.  For honey bees, the risk of death is worth the use of the stinger.  Most animals will be deterred by the pain of the stings they receive if they disturb a honey bee nest and will stop their attack before they destroy the honey comb or the queen.  Honey bees sting to protect their resources from other animals that might want to steal from them, and those resources are important enough to the colony as a whole to risk dying to protect them.

Ants and many wasps are similar to honey bees: they all have stingers and venom sacs.  Ants and wasps tend to have smooth stingers though, so they are able to pull their stinger out of their victims intact and may sting more than once.  This is something I experienced with my ant sting.  I was actually stung in 3 different places, though only the sting in the photo involved enough venom to leave a lasting mark.  Ants and wasps use their venom for many different reasons, ranging from protecting their nest or themselves (like in the honey bees) to immobilizing prey items or host organisms.

So just how do stingers work?  First, let me share a fun fact: all bees, ants, and wasps that sting are female.  That’s right – males don’t sting!  This is the case for many biting and/or stinging insects actually, but particularly so in the Hymenoptera.  Consider then what females have that males do not.  Any ideas?  If you thought about the differences in their reproductive systems, you’re on the right track!  Many insects have external (and sometimes retractable) tubes through which eggs are laid.  These tubes are called ovipositors.  The hymenopterans have evolved a further use for their ovipositors – a venom delivery device.  Some hymenopterans, like some of the ichneumonid wasps (wasps that have REALLY long stinger looking things coming off the back!), use their ovipositors to drill into wood, locate beetle larvae or other insects that are already inside the wood, immobilize the insect larvae with their venom, and then lay eggs on these prepared host insects.  In these insects, the ovipositor is used as both a egg delivery tube and a venom delivery tube.  The ants and many of the bees have evolved a second tube that is now used specifically for eggs, leaving the original ovipositor to act solely as a stinger.  Males do not lay eggs, so they do not have ovipositors.  Because they do not have ovipositors, they never had the equipment necessary to develop stingers.  So, all stinging hymenopterans are female.

That means that the ant that stung me was a female.  As were all of the hundreds of other ants that have stung me in my lifetime.  I seem to be particularly attractive to ants and get stung all the time!  Unfortunately, I believe I am becoming sensitized to ant, bee, and wasp venom as well.  Some people start developing sensitivities to hymenopteran venom over time, especially when they are stung often as I am.  When I was a child, ant, wasp, and bee stings left only little red marks that usually went away within a day.  The last time I was stung by a wasp, I had a horrible reaction, a swelling that ended up about the size of a dinner plate that was rock hard.  And the last few ant stings I’ve gotten have given me the big welts you saw in the photo.  This likely means I’m becoming sensitized – I’m having stronger and stronger reactions every time I get stung.  Not all people become sensitized to venomous hymenopterans and some people will have the same reaction every time they are stung through their entire lives.  I am unfortunately not one of these lucky people and might end up needing to carry an epi pen with me in the future in case I get stung and go into anaphylactic shock.  Not a happy thought, but there’s nothing I can do about it either.

In the meantime, I have to wear shoes that don’t touch the welt on my foot so it will heal more quickly and doesn’t hurt so much.  And I’ll also start looking in my shoes before I put them on!  At least until the ants find a better place to live than my house and move on.  I’m really looking forward to that day…


Text and images copyright © 2009


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