I got a request to do a blog post on chiggers from a
Bloomington community member, James, when he came to talk to me at a nature outreach table I did in collaboration with my friend who is an environmental educator for the Bloomington Parks and Rec Department at our local farmer’s market a couple Saturdays ago.
I figured, why not!
Anyone who has done field work in Indiana and other places
in the more southern US have experienced them and their terribly itchy,
lingering bites. They always seem to be in those places where you never want
bites, like under your arms and along the waistband of your pants and other
places where your clothes are up close to your skin. You never seems to get the
bites until the day after you’ve been outside, which is quite annoying, and
sometimes you get more bites even though you haven’t been outside again. These
bites also stay itchy for way longer than mosquito or tick bites, and itch a
lot more, so really the worst kind of bites.
Some of the questions James asked me where, what are
chiggers exactly? Can you see them? What causes these bites? Is there a way to get rid of them or prevent
being bitten? These are all great questions and there are a lot of
misconceptions about them too, which I will try to address too.
Chiggers are the larval stage of a trombucid mite, sometimes
called “red bugs.” The nymph and adult stages eat plant material and do not
interact with host animals. The larvae are very small and are difficult to see
with the naked eye. One of my lab-mates did see one crawling on her leg and
scraped it off onto a microscope slide and then we could look at it under a
microscope. This was the first time I actually saw a chigger, it looked very
similar to the picture above.
Unlike ticks, these mite larvae feed on the skin cells of
their hosts. They use their mouthparts to burrow into the skin of the host and
uses a specialized enzyme to liquefy the outer layer of skin so it can be
ingested, creating a stylostome (kind of a tube into the host’s skin). This is
probably why the bites are sooo itchy and stick around for a long time, because
there is more damage or manipulation of the host skin, as opposed to insertion
of the mouthparts of a tick or mosquito. The bites also look like they have a red dot in the center, which is the stylostome, and sometimes the mite itself. The host’s immune response to the
chigger saliva and to the bite that can cause irritation too, which is similar
to other ectoparasite bites. The bites usually form after the mite has
extracted itself from the stylostome. However, if the chiggers aren’t washed
off the skin they can move around and create more bites even after you come
back from being outside. Some people say putting nail polish on the bites will
suffocate the mite and kill it, since they are still inside the bites when they
appear. This might work to stop them itching, or stop you itching them, but
since most of the mites would have removed themselves before you see the bites
it won’t kill them.
The places that are usually the worst for chigger bites are
scrubby areas with a lot of grassy or brushy vegetation. The old-wives-tale is
that blackberry patches are the worst for chiggers, which is kind of true, and
this may be because blackberry bushes provide good habitat for animals like
mice and rabbits that chiggers use for hosts. A traditional preventative
measure against chiggers is to put sulfur power into something like an old sock
and sprinkle it around your wrists and ankles. The chiggers don’t like the
taste or smell of the sulfur and are deterred from biting. This works pretty
well, and a Bloomington soap maker makes a soup that has sulfur inside it,
which is a must for people who do field work. This soap doesn’t make you reek
like rotten eggs, you can smell it if you put your nose up next to your skin,
but it does do a pretty good job of at least reducing the number of chigger
bites you’ll get. My same lab-mate that put the chigger on the microscope slide
did a little experiment with this soap. Half of her field crew used the soap
before field work and half didn’t, and the ones that used the soap had many
fewer bites. That’s good enough for me, and I stock up on this soap before each
field season! Taking a shower as soon as you come back from being outside and
scrubbing hard with something scratchy, like a brush or a luffa, can help
scrape off any chiggers that are still on your skin. Chiggers can hang out on
your clothes too, so putting them in the freezer for 24 hours or washing them
on hot can kill them.
So, while chiggers are related to ticks, they are the larval
stage of a mite and do not suck blood. Most chiggers don’t transmit any
diseases because they don’t come into contact with the hosts’s blood (some chigger species in southeast Asia can be disease vectors, but none are in North America). We sometimes find them on our rodents. There probably
isn’t a way to avoid getting any bites, but you can do a few things to prevent
them. Hopefully this comes soon enough for some of you to reduce any painful
side-effects of spending time in the great outdoors!
Some of my sources, in addition to talking to some of the local ectoparasite experts over the years:
