Summertime Scratching
If you are a regular reader, you have probably noticed we try to invigorate our readers with the wonder of nature and we try to excite curiosity in everyone in every story we tell. Much of this is done through peeling back layers of the science of some of the species we have at Harmony Hill, hopefully giving you a few glimpses at nature that make you exclaim, “I didn’t know that!” This installment is designed to spotlight a genus of arachnids that we are certain you know, but one that is often shrouded in myth and old wives’ tales. And, when we’re done with our conversation, we hope you’ll be able to say, “Hey… I didn’t know that!”
Summertime brings warm weather, sunshine and a longing to be outside more than usual. We are all walking through the fields and the forests more, cookouts and picnics find us eating in the great dining hall of nature and, even drives are more outdoor focused, as windows are down, sunroofs are open and convertible tops are dropped. And, like you, those extra hours walking in the woods and those picnics may invariably find us scratching some itchy, red bites on our ankles, waist and the backs of our knees.
Growing up, our parents and grandparents often warned us about sitting in pine straw or walking in tall grass. Whether they called them “chiggers” or “red bugs”, they would tell us horror stories of bugs that will bite you, bore into your skin and cause you intense itching for weeks! For those of us not wise enough to heed their advice, we did find ourselves itching, scratching and suffering from bites we were told could only be healed by thorough and thick applications of fingernail polish.
Some of the advice they gave us was true; but, much of what we were told of “chiggers” or “red bugs” was not based on fact. Let’s look more closely at the natural history and see what the fact are and dispel a myth or two along the way.
First of all, what is a chigger? Chiggers, or red bugs, are not insects at all; but, are arachnids that are more closely related to scorpions and ticks than they are to mosquitoes. Classified as a type of mite, adult chiggers, found in the Eutrombicula genus, exhibit the classic arachnid characteristic of eights. Adult chiggers, of which there are dozens of species, are also red in color, giving them their common name of “Red Bug”. However, many species of adult mites can be reddish in color and that is not a definitive identifying field marking.
Rather small arachnids, adult chiggers measure about 1.25mm (0.05 inch, or 1/20th of an inch) and become active when ground temperatures reach about 60F (15.5C). For much of the southern United States, that is a large chunk of the calendar year, making chigger season March-November, most years. Adults can be seen by the naked eye and, perhaps, you’ve seen them crawling along blades of grass. Adult chiggers pose no threat to us, as they do not bite or feed on humans. They do; however, make a very. Good living feeding on other insects and even insect eggs.
If adult chiggers aren’t the problem, then what is?!
For that answer, let’s look at the life cycle of this arachnid.
There are four main stages in the life cycle of a chigger: egg, larva, nymph and adult, that usually occur over the course of a couple of months. However, depending upon the time of year and the location, it may take nearly a year to complete the life cycle. (There is also a very short, but recognized prelarva stage in some mite species.) We can take the egg stage of the life cycle out of the conversation, as the eggs are of no danger to humans. The nymph stage is very similar to the adult stage, also having eight legs and the same diet as the adult. That leaves us with the unique larval stage, with just six legs and a hunger for semi-digested skin cells, as our culprit!
The larval stage of the chigger, as mentioned, is quite different from the adult. Having just six legs, it is also considerably smaller. Chigger larvae measure an incredibly tiny 0.25mm (that’s just a miniscule 0.001 inch, or 1/100th of an inch!) I had a professor in college once say that you could easily fit 4-6 chigger larvae inside a 12-font period! (Just like the one under the exclamation point you just read)
Adult female chiggers will lay eggs on vegetation and, when they hatch, the larvae are not very mobile. This means they will be found in large numbers in very specific areas. This clumping is why chigger bites come in such large numbers and why you sometimes get no bites in the same geographic area. It is not an exaggeration to say you could have well over 100 chigger larvae in one spot and have absolutely none just a few feet away.
Chigger larvae thrive in moist, shady areas, where grasses, forbs and other vegetation is found. They are particularly fond of creek and stream banks, where tall hardwoods keep shade over vegetation below. Some chiggers can also be found in areas that seem much drier, such as in mulch (think pine straw).
The larvae will sit on that vegetation and wait, indiscriminately, for any potential victim to walk past to feed upon. And, it is that feeding that leads us to the bites that itch so badly and are prone to become inflamed and even infected. The larvae will climb up onto the animal (or human) and find a thin portion of skin to bite.
They do not have strong mouthparts and must find a thin place to pierce the skin. In most mammals, that is usually at a hair follicle. On humans, that is around the ankles, the beltline and groin area, the backs of knees and armpits. That also coincides with where clothing fits the tightest; where socks, belts and sleeves sit. When they bite, they DO NOT burrow into your skin and stay there to feed and irritate you. They do; however, excrete saliva that dissolves skin cells, and it is that liquified cell structure that they feed upon.
Your body’s natural immune reaction even helps them with this process. The red dot atop the bite is the top of a structure called a stylosome, which is a hardened tube that allows the digested skin cells to flow out of your body. The stylosome becomes a straw in which the chigger larva can sit and feed.
Unlike their tick relatives, chigger larvae do not have mouths that are designed to allow them to latch and hold on with strength. They can be brushed away and one of the easiest ways to get them off you is a good soapy shower or bath.
The larvae can sit on victims for as many as 2-4 days; but, that is very rare with humans. Most humans only have chiggers feeding on them for a couple of hours. By the time the itching begins, the damage has been done and the body’s histamine response is in full force. Itching and swelling begin a few hours after the bites and can become intense and continue for several days. It is important to wash very well after being in chigger habitat and it is important to take steps to prevent bites to begin with.
By wearing long clothing, tucking pants into socks and shoes, avoiding taller vegetation and not sitting or lying in places where chiggers can be found, you can minimize the opportunities for them to crawl on you and bite you. If you use a repellent of any kind, it is best to pretreat areas around the shoes, ankles and beltline before going out.
As far as treating bites that have happened, simple topical treatments for itching work best. Fingernail polish does not smother the chigger, as they do not burrow into your skin at all. However, be mindful not to scratch the bites aggressively and risk infection. Secondary infection is the most common medical issue after chigger bites become present.
An artist’s rendition of the adult stage of the chigger (left) and the larval stage (right). Image courtesy of Texas A&M. https://extensionentomology.tamu.edu/publications/chiggers/