Garden centipedes, also called garden symphylans, are not insects, but members of the class Symphyla. Species of this class are common soil arthropods worldwide. Symphyla are small, whitish "centipede-like" creatures ranging from less than 1/8 inch up to about 5/8 inch (or 1/3 inch for garden symphylans). Other names for this pest are garden symphylan and greenhouse centipede. Despite its name, garden centipede is not a true centipede at all, but only resembles that group, because centipese feed on other insects, but garden centipedes are pests that eat plant roots. One way to tell them apart is by the number of legs they have: symphylans have 12 pairs, while centipedes have at least 15. Garden centipedes live about four years.
Garden centipedes are quite small rarely exceeding 1/3 of an inch (8.5 mm). You need a magnifying glass to distinguish them from other soil inhabiting creatures with which they may be confused. These include springtails, young millipedes, and centipedes. Symphylans are very active and fragile. Though their color may vary, depending on what they have eaten, garden symphylans are generally whiter and smaller than true centipedes.
The female lays about a dozen white eggs in the soil and remains with them until young emerge. The first instar nymphs emerge from the eggs with 6 pairs of legs and 6 antennal segments. The second instar looks more similar to the adult. Each of the six subsequent molts results in the addition of a pair of legs.4
Garden centipedes can potentially damage a wide range of vegetables, small fruits, and flowers. Most serious damage occurs to belowground parts of plants. The damage caused to roots may initiate root rot inflicted by bacteria and fungi. Some damage signs are specific to the crop. The leaves of tomato, for example, take on a bluish tinge and the plant becomes very stunted. Lettuce plants do not develop a heart. Garden centipedes are also decomposers that feed on decaying matter. High rates of raw to partially decomposed organic matter additions are the main stimulant to these pests.1,2,4
To determine if the damage is caused by garden centipedes, lift poorly growing plants and quickly submerge them in a bucket of water. Centipedes will come out of the soil and float up to the surface. Ten or more centipedes around the roots of a single plant are enough to signal concern.
Control can be extremely difficult due to symphylans' vertical movement in the soil, the comlexity of sampling, and the lack of simple, effective control methods. 5 Tilling the soil is still one of the most effective method of control. By physically crushing garden symphylans, the populations can be reduced substantially, although it may also harm key garden symphylan predators such as true centipedes and predaceous mites. Pesticides may have the effect of both killing garden symphylans and repelling them from the surface soil.3 Crop rotation may help reduce the populations of symphylans. Populations decrease significantly in potato crops. They are also lower after a spring oat winter cover crop. Manure applications tend to increase the populations.5