It is an unfortunate truth that chickens, just like every other form of livestock, need to be wormed.  There are a lot of reasons to do this, and different methods available.  

Why worm?
Chickens, because they forage off the ground, can easily pick up a worm infestation.  In fact, it's almost inevitable.  The most common source of infestation is ascarid worms, also known as large roundworms.  Threadworms, tapeworms, and gapeworms are all also frequently present.  

How do I know if my chicken has worms?
If it's a chicken, it probably has worms!  The symptoms of a very serious infection include lethargy, a pale wattle, reduced egg laying, and "unthriftiness" which means that the chicken eats a lot but fails to put on weight and even loses weight.  

By the time your chicken is showing these signs, the infection is very serious indeed.  The best reason to treat worms on a regular preventative basis is that once a chicken is visibly sick, it may already be too late for her.

It's safe to assume that if it has been more than six months since the last time you wormed, then your chickens have worms and should be wormed again.  Worms in chickens are like fleas with cats or dogs - it's safe to assume that everyone's got 'em.

How do chickens get worms?
Roundworms, the most common kind of parasitic infection, are passed along through eggs in the soil - as are threadworms, and several other varieties of parasites.  The infected bird (either a chicken or a passing wild bird) passes out worm eggs in its poop. After 10 days these eggs hatch into the larval form.  The chickens then ingest the larvae by preening, pecking, eating food off the ground, etc.

Deep litter systems are excellent breeding grounds for worm infestations.  Although the deep litter system is convenient for the keeper, and ecologically efficient, it's worth considering your chickens' health in this respect.

Gapeworms are communicated through a transitional host.  Your chicken gets them by eating an infected snail, slug, or earthworm.

What do I use to worm my chickens?
There are many non-toxic holistic measures recommended online.   These include diatomaceous earth, apple cider vinegar, crushed pumpkin seeds, flaxseed, and chopped garlic.  Be aware that these are not tested in a lab, and may not be very useful.

The two most common medications for treating worms in chickens are piperizine and ivermectin.  Piperizine is sold over-the-counter, and is very effective against roundworm.  Ivermectin is only available with a prescription, and is a broad-spectrum medicine that kills all forms of parasites (both internal and external).

Where can I buy chicken wormer?
Your regular feed store is an excellent resource.  They will certainly have a medication available, most likely piperizine.  (The kind I buy is pink, cherry flavored, and called "Pig Swig.")  If your flock has a very serious case of worms, an avian vet will be able to prescribe ivermectin.

How do I worm my chickens?
There are several different methods, depending on the specific medicine that you get.  Be sure to follow the instructions!  Some medications are simply added to their drinking water, others are dropped on the back of their heads like a flea medication, and still others have to be force-fed in a paste form.

What about the eggs?
Don't eat your chickens' eggs after worming!  Follow the manufacturer's instructions.  Most wormers have you discard your hens' eggs for 14 days after treatment.

Creative Commons-licensed image courtesy of Flickr user Benimoto