Tapeworms, also known as cestodes, are a type of parasitic flatworm that can are commonly found in backyard or free range chickens. There are more than 4,000 different species of tapeworms that affect animals and 35 percent of those are found in wild and domestic birds. Tapeworms are ribbon-shaped, flattened, segmented worms which are initially only a 1/6 inch (0.42 cm) long. As they grow, tapeworms increase in length by adding segments to their body, and are able to increase to 12 inches (30.48 cm) in length.
Tapeworms anchor themselves into the chicken's intestinal wall within their digestive tract, where they absorb the nutrients, instead of the chicken. Tapeworms won't actually cause physical damage to the intestinal wall, however by taking all the nutrients away from the chicken, it is still damaging to it's health, resulting in stunted growth/weight loss, nutrition deficiencies, lower egg production, and increased susceptibility to secondary pathogens, due to an impaired immune status.
Tapeworms have an indirect life cycle. They use arthropods and other invertebrates as intermediate hosts (snails, slugs, beetles, grasshoppers, ants, earthworms, termites, and houseflies). Chickens become infected by eating the intermediate host. Once the host is consumed by the chicken, the tapeworm larvae that was initially contained within its host gets released, into the chicken's gastrointestinal system. From there, the tapeworm larvae attach themselves to the intestinal wall, where they continuously absorb nutrients from food eaten by the chicken, instead of the chicken absorbing it. Once the tapeworm has matured into an adult, it sloughs off part of it's segments which also contain eggs, which gets passed out of the intestines and into the chicken's feces and contaminating the surrounding environment. Intermediate hosts will consume the sloughed tapeworm and its eggs, where the eggs will grow into larvae, and the cycle repeats itself.