Welcome to BYC, Diane! I grew up in chigger country. Chickens don't eat chiggers (unless it's accidental in eating vegetation). They are so small that I doubt chickens can even see them. I know I can't see them unless they are bloated with blood. Then they look like little red dots. Actually there are some ways to rid your yard of chiggers without using pesticides. Make sure you mow and cut the grass short, especially around the edges where the grass meets other plants or woody areas. Remove any accumulated leaf litter and trim any landscape plants. Remove any brushpiles from your property. Chiggars avoid sunny areas, so eliminate anything feasible that provides shade for them. After you have done these preliminary things (at least as much as is possible), buy some powdered soil sulphur and spread it all over your yard early in the morning while the sun is still low in the sky. Be careful when handling the sulphur. Use gloves, eye protection, and a mask over your mouth and nose. Afterward, water your yard for 30 to 45 minutes. The watered sulphur will not harm your chickens, but it should rid the yard of chiggers. We used this procedure on our yard in northeast Texas and it worked very well. Good luck.