So. In the last few months, I've spent an awful lot of time thinking about chiggers.
As you may know already, chiggers are the juvenile stage of a mite. The adults are harmless, and not interested in animals, but in order to mature, they need delicious animal flesh. To that end, they climb up things that smell tasty, and find a pore or hair follicle to attach themselves to, and go to town.
That's an important bit. Their mouth-parts can't actually bite you. They need to use the preexisting holes in your skin to feed, which they do by injecting enzymes, and sucking out the cell soup that results. Your body produces a response to this, and that's what causes the itching. Most of the time the chigger is long gone before you will even begin to itch. Aside from the itching, they're otherwise harmless, at least here in the US. In Asia and around parts of the South Pacific you can acquire scrub typhus from chigger bites, which sounds like a pretty bad time.
I'm somewhat battle-hardened when it comes to the little guys, and the fact that I have not been without a least a dozen or so bites for the last few months hasn't been a big deal. Going through a few weeks with many hundreds of them will do that to you. I would like to offer you some advice if you live in chigger country, so that you don't have to go through that experience.
Firstly: Wear long pants. Some of my research partners disagree on this, but that's mostly meant they got chigger bites on their underwear lines, rather than on their ankles. Chiggers will climb your legs until they hit a barrier of some kind, and then look for a spot to feed. That can be your sock, or where your shoe meets your ankle, or what have you. Or it can be your underwear line. Or past it. Seems like a simple decision to me. If you're constantly moving, only in chigger territory for a short time, or outside at times they're not very active (when it's cool, wet, or very, very hot), long pants tucked into your boots may be all you need.
Second: Wear repellent. DEET is supposed to work. So is picaridin (found in brands like Natrapel). However, the old stand-by is sulfur. You can use powdered elemental sulfur, or an emulsion like ChiggAway. I have made frequent use of the ChiggAway, which has the advantage of somewhat reducing the itching of existing bites. In fact, I typically apply ChiggAway on my ankles, behind my knees, around my belt line, wear long pants, spray on picaridin (which I like better than DEET) around my ankles and waist, and then tuck my pants into my boots. I don't mess around. The downside to sulfur-containing products is that sulfur is pretty much insoluble in water. Which means it doesn't wash out of your clothing, once it gets on it. Which means your field clothes will smell like sulfur for kind of a long time.
Third: Designate field clothes. It's a good idea to have a few sets of appropriate field clothes. Especially if you make use of sulfur products. Do not re-wear these without washing them (or at least tumble drying, which will kill any pests you pick up), if you can. I'm a fan of army surplus gear myself, as it is remarkably durable, has a lot of pockets, is very cheap, and I also happen to look good in olive drab. If you've been using sulfur, you can try dry-cleaning your field clothes at the end of the season. Elemental sulfur is fairly soluble in some organic solvents, and you might get lucky. I haven't tried this yet, but I may.
Fourth: Bathe as soon as possible. When you get back from field work, hiking, chasing the dog through an old field, or laying in the grass reading, take off your clothes, put them in a hamper, and take a hot shower, if you live in chigger territory. For the record, chigger territory can easily include your backyard. During one inventory on a parcel, the owner came out and warned up about the chiggers in her yard. She routinely got bitten, even when applying DEET, and had treated her yard with various pesticides multiple times. And this was a well shaded, fairly well maintained property. If you can't take a bath or shower, because there isn't one, or you're going to be in the car for a few hours, you should do two things: change clothes, and give yourself a rub down. Chiggers are rather fragile beasties, and a vigorous rub down of areas where they like to hide (behind the knees!) will kill them.
These four simple things will go a long way towards reducing the number of chigger bites you acquire while out and about in the great outdoors. People might look at you funny, and turn up their noses if you get too close, but it's a hell of a lot better than having four hundred chigger bites, believe-you-me.