Ah, summertime.  In Tucson, this is a time of extreme discomfort if you’re outside due to the blazing sun.  In other less hot places in the world and for many people, summer means a fantastic time outdoors – family vacations, camping trips, rolling down grassy hills, hiking, etc.  Unfortunately, this is also the time of year when lots of people get up close and personal with chiggers, the subject of today’s post.

That cute little guy above is a chigger.  Yes, I do actually think these things are cute, but then I’m an entomologist with a passion for gigantic insects that stab things with their beaks to pump them full of digestive chemicals to eat them and scare the living daylights out of most people, including several entomologists I know.  (I’ve got video of giant water bugs eating if you want to see them in action:  Abedus and Lethocerus!)  Clearly I have questionable taste.  Don’t let those 6 legs fool you though – chiggers are NOT insects.  Instead, they are the larval form of a group of mites (which are actually a type of arachnid) called the harvest mites.  Similarly to how insects grow wings as they transition from their larval or nymphal stages into adults, chiggers gain a pair of legs during their transformation into nymphs.  They then go from an 8 legged nymph to an 8 legged adult.

So why are chiggers so bad?  If you don’t know, you obviously haven’t experienced these nasty little predators.  They feed on the tissues of a wide variety of animals, including humans, though we Homo sapiens are not their preferred host.  There are a lot of misconceptions about feeding chiggers.  Case in point: after my first day of class as a graduate student, a big group of students decided to go to lunch where we had the most magnificent argument over the feeding mode of chiggers.  Do they burrow under your skin when they feed?  Are they in there when you notice you’ve been bitten?  Or do they bite you and fall off?  If a big group of entomologists can’t reach a consensus about how chiggers feed, it’s no wonder that so many other people are confused!

Let’s set the record straight right now: chiggers do not burrow into the skin.  That’s what ticks do, not chiggers.  Considering how similar mites and ticks look, it’s understandable that people mix the two up.  But just how do chiggers feed?  And why are they a nuisance to the people unfortunate enough to bump into them?

Chiggers are commonly picked up in fields full of plants.  There, they wait for an animal to brush up against the plant they’re on and then run onto the animal.  Then they crawl around and find a safe place to start eating, somewhere they are unlikely to be brushed off before they finish their several hour long meal.  If you’re a furry mammal, this could be anywhere and the chiggers may simply climb down into your fur and start to feed – and many animals have no reaction to their presence at all.  We relatively hairless humans have many fewer places chiggers feel safe.  Instead, they go for places where you’ve got thin skin, dark crevices, or where clothes sit tightly against the skin.  This means that most people end up with their chiggers in places like their armpits, the backs of their knees, their socks, under the bands of their underwear (tops or bottoms), and sleeve cuffs.  Once they find a good place, they latch on tightly and start to feed.

Unlike many blood feeding insects and their relatives the ticks, chiggers have very short mouthparts.  Those little dangly bits at the front end of the chigger in the picture above are the chelicerae, their mouthparts.  Now imagine the chigger in that photo shrunk down to a milimeter or a half milimeter in size, their actual size.  Like I said – very short mouthparts!  Chiggers don’t just eat the top layer of skin cells though – they go for the good stuff underneath.  To do this, they pierce the skin with their chelicerae, then inject saliva to digest the tissue and expand the wound.  The goop that is produced is slurped up by the chigger.  Remarkably, they also inject compounds into the wound that cause an immune response in the host animal, one that hardens the tissue around the bite site.  In essence, the hardened tube-shaped structure that forms (called a stylostome) is a straw that expands deeper and deeper into the host.  The chigger injects more saliva and sucks up more liquified tissue as the stylostome gets longer and longer.  That’s right!  Chiggers have tiny mouthparts, but they use their host’s own immune system to enlarge their mouthparts into a stylet like those of mosquitoes or a beak like those found in the true bugs!  Now if that isn’t amazing, I’m not sure what is.

So the chigger bites you, dissolves some of your tissue, and eats it.  Big deal, right?  Wrong!  These tiny little creatures are capable of producing some truly awful allergic reactions.  These aren’t the send you to the hospital, carry an epi-pen with you kind of response in most people.  Instead you itch.  You itch like you’ve never itched before.  Some people get massive itchy welts.  The itching is intense, so severe that people have been known to gouge welts out of their skin as they scratch and many people have reported that the pain of doing this and the ensuing scars are much easier to deal with than the itch of the bites.  Now the itching wouldn’t be so bad if it were just a few bites, but most people don’t get that lucky.  Instead they get tens or hundreds of bites from many individuals at one time (chiggers tend to be clustered together) that are located in inconvenient places (want to be observed scratching your armpit or your bra straps vigorously hundreds of times per day?) and don’t go away for 5-10 days.  That’s right – these little tiny animals can cause massive itching for 10 days or longer!  (Are you itchy yet?)

It’s much easier to avoid chiggers than deal with the itching they cause later.  If you know you’re going to be out where there might be chiggers, there are some precautions you can take to keep them off you.  First, wear long pants and long sleeves.  Tuck your pants into your socks for extra protection.  The less skin you have exposed the better.  Avoid walking through brush and stay on trails where possible.  Finally, get out of your potentially contaminated clothes and take a shower, scrubbing thoroughly, when you get home.  Chiggers can roam around for several hours before they settle on a place to eat, so showering can help wash them off before you are bitten.  If you are bitten, well…  I recommend a trip to the pharmacy to get the best hydrocortisone you can buy and hope for the best.

For a more thorough account of chiggers, I highly recommend reading Dark Banquet by Bill Schutt.  It’s a book about sanguivores, also known as blood-feeding animals.  It’s a fascinating books and had a great section on chiggers.  In fact, reading that section prompted me to write this post in the first place!  There is also more detailed information at the website where I found the illustrations, http://animals.howstuffworks.com/arachnids/chigger.htm, including some photos of welts formed due to chigger bites.

Enjoy your summer and avoid chiggers as well as you can!

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