Red mites on chickens-Signs/Symptoms & Treatments. Red mites also called Dermanyssus gallinae burrow  into wood usually in the hen house walls and nest boxes. They are nocturnal and rarely come out during daylight hours but do come out at night and will bite your chickens. They do not fly but can cause serious illness and death in poultry flocks because they cause the birds to become anemic, cause skin irritation, feather loss, less egg production and can eventually kill the chickens if left untreated.

How to tell if your chickens have red mites:
Rub a white cloth underneath the perches where the hens roost. If there are blood stains on the cloth you have red mites in your hen house and you need to act quickly if you want to save your flock.
Signs to Look For:

• Increase in food consumption
• Clumps of red mite under perch
• Blood under perch and in nest boxes
• Infestations around perch ends & cracks
• Grey 'dust' (mite excreta) around areas of infestation
• Chickens not wanting to roost in house at night
• Weakened condition
• Restlessness
• Pale comb and wattles
• Drop in egg production or stop laying all together
• Blood spots on eggs
• Birds are restless at night 
• Severe skin irritation from mite bite

How to get rid of red mites on your chickens

• Creosote can be used and it is recommended that it be applied by a professional but you can do it yourself. 
• Paraffin Wax-Paint Paraffin into cracks and crevices. Smearing a mixture of Paraffin and Vaseline into cracks and crevices. Vaseline is used frequently by poultry keepers to get rid of scaly leg mites. It smothers the mites.
• ​Steam Clean-Steamers used for stripping wall paper can be used to get into cracks.
• Pressure Washers can be used to spray into cracks to wash out mites.
• Double-sided sticky fly papers / double sided sticky tape on the underside of the perch and / or around ends of perches.
• Coke (no particular brand) poured into cracks to wet the mites apparently works by dissolving the waxy outer coating of the mite which then causes them to dry out, dehydrate and die.
• A dust bath can really help the birds with mites and lice and is their natural way to getting rid of external parasites. Dusting powders can be added to dust baths (like Diatomacious Earth) so the birds get it into the places you have missed. When mites hop onto your birds at night, they will rub against the diatom. 
• Regular thorough cleaning of hen house floo,r ceilings, walls, roosts and nest boxes
• MiteX, a natural non chemical insecticide can be used in poultry houses and in feed storage areas without risk to the birds, feed or any workers. The MiteX powder, which has extremely high oil absorption, is highly effective at attaching itself to and then lacerating the waxy surface of the insect as they move through it (Daniels, 2008).
• Permethrin
• ​Ivermectin
• Food grade Diatomaceous Earth can be used to dust chickens, sprinkled on top of feed once a week, sprinkle on floors, bedding and runs.

Reference:Daniels, Tim.(Sept. 3, 2008). Red Mites. PoultryKeeper.com.  ​https://poultrykeeper.com/red-mite/red-mites/