Earthworm Pests (Mites)

White or Brown Mites
White or brown mites are not predaceous and tend to feed only on decaying or injured worms. During infestations, however, these mites can devour much of the food in earthworm beds, depriving worms of needed nutrients. This increases worm growers' costs and time spent feeding worms. Mite populations at high levels can also cause worms to stay deep in the beds and not come to the surface for feeding, resulting in poor growth and reproduction.


Red Mites
There is a red mite that is a parasite of earthworms. They attach themselves to worms and remove body fluids and can feed on earthworm egg capsules. These mites first appear as small white or gray clusters, resembling mold. Magnification will reveal clusters of juvenile red mites in various stages of development. The adult red mite is has an egg-shaped body, is bright red, and has eight legs


Grain Mites
Grain mites are very small (1/64 - 1/32 inch), slow-moving, pearly white mites with some long fine "hairs" on their abdomen. These mites can feed on a variety of processed or finely ground grains, wheat germ, yeast, cheese, powdered milk, flour, or mold spores. They develop rapidly in 90% humidity and a temperature of about 77o F. Grain mites require a minimum relative humidity of about 65% so dry air is their enemy. They do not attack earthworms but their waste, shed exoskeletons, and dead mites can quickly foul the earthworm media. Overcrowding from heavy infestations will force mites to move off in search of other food sources. This "spill over" can produce a fine dust-like layer of these mites on areas around the worm beds. Some people can have an allergic reaction from exposure to the mites or their shed exoskeletons.


Here are some factors associated with mites in earthworm beds.


1) Too much water - Beds that are too wet create conditions that are more favorable to mites than to earthworms. Avoid excessively wet beds by adjusting watering schedules, improving drainage, and turning bedding frequently.


2) Overfeeding - Too much food can cause an accumulation that will ferment. This will lower the pH of the beds. Adjust feeding schedules so that all feed is consumed within a few days.


3) Excessively wet or fleshy feed - Vegetable matter with a high moisture content favors high mite populations. Limit the use of such feed, and if high mite populations are discovered, do not add any more until the mite population is under control.


These conditions also will favor problems with flies and other insects. Pest prevention is the greatest control program and pest exclusion, through screening, is the greatest tool. There are no pesticides that are labeled for mite (or general pest control) in worm beds.


Mite Removal
Several methods have been suggested for removing mites from earthworm beds. Bear in mind that any type of mite removal, physical or chemical, will only be temporary unless worm bed management is altered to make conditions less favorable for mites. The following techniques range from low- to high-intensity measures.


Method #1 -- Uncover the worm beds and expose them to sunlight for several hours. Reduce the amount of water and feed. Mites will not like this environment and they may leave the worm beds.


Method #2 -- Place moistened newspapers or burlap bags on top of the beds, and remove the paper or bags as mites accumulate on them. Repeat this procedure until mite populations are substantially reduced.


Method #3 -- Place pieces of watermelon or cantaloupe rind or potato slices on top of the worm beds. Mites are attracted to the sweetness of the rinds or peels and will accumulate on them. The rinds or peels can then be removed and dropped in water or buried.


Method #4 -- Water heavily, but do not flood, the worm beds. Mites will move to the surface, and worms will stay below the surface. Use a hand-held propane torch to scorch the top of the bed and kill the mites. This procedure may be repeated several times, at three day intervals, if needed.


Method #5 --Use a light dusting of sulphur to kill the mites. After soaking the worm bed with water and causing the mites to surface, apply a rate of 1/16 ounce of sulphur per square foot of bed surface. Sulphur should not harm the worms, but in time, it may increase the acidity of the bed and reduce earthworm populations.


Popular literature on mite removal from earthworm beds is somewhat contradictory. In the past, some chemical pesticides have been used in worm beds. However, most pesticides have since been shown to have the potential to harm humans and recommendations for such treatments are not given here. Although newer, safer, miticides exist, sufficient scientific research has not been conducted in worm beds to merit mention at this time.