How can earthworms be harmful

General settings registry. Division Home. Division of Agricultural Sciences and Natural Resources. People use them as fishing bait. Others toss them in their gardens to help aerate the soil. They also can be used in compost piles.

How did the nonnative worms get there, how many are there and are they going to be a problem? Suggestion Box. Because of dry conditions, earthworm populations in Pennsylvania are low in the summer. Earthworms can live under submerged conditions if the oxygen content of the water is high enough. In most cases, however, earthworms will die when exposed to excessive waterlogging.

They move to the surface when the soil is saturated to avoid suffocation. Most earthworms don't tolerate temperatures below freezing, nor do they tolerate high temperatures. They can move down into the soil to escape these adverse temperatures. Earthworms commonly found in agricultural fields thrive at neutral pH, but can tolerate a pH from 5. Earthworms prefer soils with loamy texture.

Coarse sand can be a negative factor either because the abrasive action of sand grains damages their skin, or because these soils dry out more easily. In some studies, clay soils had fewer earthworms than lighter-textured soils. The reason for this phenomenon is not clear. Quantity, quality, and placement of food influence earthworm populations. Earthworms eat organic residue that needs to be present in sufficient quantity. The quality of residue is also important. Residue with a high carbon to nitrogen C:N ratio is not very palatable for earthworms.

Manure can help make it more palatable. Packed manure is an excellent food source for earthworms. In some cases, residue has to undergo some weathering before earthworms are able to digest it. Topsoil dwellers need smaller particles than subsoil dwellers, which can use large leaves, for example. The placement of food becomes a critical issue for some earthworm species. Topsoil dwellers prefer small organic residue particles incorporated into the soil, but subsurface dwellers need residue at the surface of the soil.

Soil and crop management practices can influence many soil properties that affect earthworms Fig. Some practices can have immediate effects on earthworms, whereas others may gradually change earthworm population and activities over several years. So when you are considering management options, you should also think about their effects on earthworms.

Some of the more important management effects on earthworms are described below. Figure 2. Soil tillage greatly affects earthworms Table 1.

The burial of crop residue and manure by tillage favors topsoil dwellers over subsoil dwellers. In long-term clean-tilled fields, nightcrawlers are scarce. This is another reason earthworms are less numerous in clean-tilled fields compared to no-tilled fields. Tillage brings earthworms to the surface where they are subject to predators such as birds.

Total earthworm populations in long-term no-tilled fields are typically at least twice those of clean-tilled fields. Providing earthworms with a diverse diet is important. Crop residue of leguminous species low C:N ratio is more palatable to earthworms than that of mature grass and grain species high C:N ratio. However, a legume such as soybean produces very little crop residue, which limits the quantity of food available to earthworms.

Earthworms thrive in grasslands and alfalfa. In one grassland study, 70 earthworms were counted per square foot more than 3 million earthworms per acre. If crop residue is removed, earthworms lose their food source. Use of a cover crop that is left in the field or removal of only part of the crop are ways to feed earthworms.

Manure is a food source for earthworms. It also makes crop residue with a high C:N ratio more palatable to earthworms. Manure stimulates crop residue production because of its fertilizing effect, increasing the food supply for earthworms. Liquid manure can have a temporary depressing effect on earthworms due to its ammonia and salt content.

After this effect has subsided, however, earthworm populations tend to increase. Sludge and compost can greatly stimulate earthworm populations by providing a quality feedstock for them. There is good evidence that most inorganic fertilizers favor the buildup of large numbers of earthworms, probably due to the increased amounts of crop residues being returned to the soil. Anhydrous ammonia and ammonium sulfate have been found to have negative effects on earthworms.

This may be due to the acidifying effect of this fertilizer, but also due to the toxic effect of ammonia. Liming to neutralize acidity stimulates earthworm activity. The effects of pesticides on earthworms depend on the type of pesticide and its rate of application, earthworm species and age, and environmental conditions. Appendix 1 gives test results of pesticide toxicity on earthworms.

The studies simulated normal exposure rates of pesticides commonly used in field crops. The table summarizes a great number of different studies that used widely varying methods of evaluation and should therefore be used with caution. Most inorganic chemicals tested are no longer in use as pesticides. Based on the limited amount of information available, these chemicals do not seem to be very toxic to earthworms, except when they accumulate in soil over a long period of time.

Organochlorine insecticides were extensively used from the s to the s, but are not used in large quantities today. Endosulfan and lindane are moderately toxic and probably toxic at normal exposure rates, respectively. Some organophosphate insecticides, such as acephate, azinphos methyl, chlorpyrifos, ethoprophos, ethyl- parathion, and phorate are very toxic to earthworms.

The other organophosphate insecticides listed are nontoxic to moderately toxic to earthworms. Carbamate insecticides and fungicides are very toxic to earthworms. Carbaryl and carbofuran, both commonly used in field crop production, are extremely toxic to earthworms. Pyrethroid insecticides, on the other hand, have not been found to be toxic to earthworms. Of the other fungicides tested, none were found to be toxic to earthworms except carbamate fungicides such as benomyl and carbendazim not listed.

Most herbicides are nontoxic to earthworms, although some, such as 2,4-D, pendimethalin, and simazine, are toxic at high exposure rates. Similar to that of humans, pesticide health risks to earthworms depend not only on the toxicity of the chemical but also on the exposure to it.

On the other hand, earthworms that crawl on the soil surface such as nightcrawlers have a higher exposure to surface- applied pesticides than those feeding and burrowing below the soil surface.

On the other hand, pesticides injected in a small slot in the soil such as the seed slot may not come in contact with many earthworms and therefore will not pose a significant threat for the population at large. Remember that earthworms are most active in the spring and fall under favorable temperature and moisture conditions. The movement of earthworms through soil helps to loosen and mix soil, preventing compaction. In addition, the breakdown of organic matter as it passes through the intestines of earthworms increases soil water-holding capacity, notes the University of California Agriculture and Natural Resources.

Soil pH levels are somewhat neutralized by earthworm activity, as earthworm castings are close to soil pH of 7. The fertility of soil increases because of the composting effect earthworms have on decaying plant matter, advises the University of Illinois Extension. As plant debris passes through the intestines of worms and is excreted in castings, nutrients are liberated, increasing the nitrogen, potassium, phosphorous, calcium and magnesium levels of the soil.

While earthworm castings improve soil quality and fertility, when they are brought to the surface and deposited in large piles, such as those left by some types of earthworms like nightcrawlers Lumbricus terrestris , they can be unsightly and cause lumps on the lawn or in the garden, advises the University of Minnesota Extension. Raking soil while it is lightly moist helps disperse castings, which are like free organic compost for the garden. Alternatively, lightly till castings into the soil using a garden hoe or other tilling implement.

Moles eat earthworms, grubs and insects, advises the University of Minnesota Extension.