Broodies are prime targets for such pest because they are relatively immobile. The broody should be sprayed or dusted with an insecticide made for the purpose before she starts to sit and should be treated again on a weekly basis. The legs of chickens should also be watched for any sign of scaly leg mites, which can be killed with oil or kerosene. Remember, a chicken asked to incubate waterfowl eggs must set for a full week longer than would be necessary for her own eggs. She needs an extra measure of care, as a result.
Some broodies have better habits while incubating eggs than others.
For example, some females will foul the nest with their droppings periodically which greatly increases the likelihood of bacterial contamination. All broodies should be banded and records should be kept to insure that broodies which have good habits and are reliable are retained. Perhaps the biggest problem with natural incubation is having a broody ready to go when one needs one. By ready to go, I mean a broody which is in the mood to set and has done so for a minimum of 48 hours. Often, semi darkness tends to stimulate a duck or chicken to go broody a little faster.