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Identifying Earthworms

Orange Clitellum

Only try to identify reproductive adults: those earthworms which have a well defined clitellum. The clitellum is usually a different colour than the earthwormís body and located close to the head of the earthworm. The clitellum is normally greyish-white, but it can also be bright orange within the same species. The bright orange colour indicates that the earthworm is in heat, and does not mean that this is a different species of earthworm.

Follow through the illustrations on the Taxonomic Key until you have identified each adult. A detailed illustration showing all the external features of the earthworm, including a size chart, can be found on the General Earthworm Diagram. This diagram highlights all the physical features youíll need to correctly identify your earthworms. Patterns are the key to identification! When identifying an earthworm, it is important to look at the patterns on its clitellum. The fine details are not as important, or even as clear, as stepping back to observe the general patterns.

Identifying earthworms

Are there any tips I need to know before I start identifying my earthworm?

Before you begin the identification process, there are few important things that you should keep in mind. First of all, make sure your hands are moist and free of soap or lotion as these can irritate earthworms, and make them difficult to handle. Itís a good idea to keep a spray bottle of water around to moisten the earthworm and your hands when they become dry. Secondly, when you are looking for certain physical characteristics on your earthworm, look for patterns and not small details.

The number of segments from the peristomium to the clitellum and the number of segments which make up the clitellum are species specific in earthworms. This means that if two earthworms have different numbers of segments to the start of the clitellum, they are different earthworm species.

How to use the Earthworm Taxonomic Key

The key you will be using is organised as a flow chart. It starts with very basic characteristics and becomes more specific at each level. As you move down one branch of the flow chart, you will be eliminating earthworms and will be left with only a few earthworms to pick from.

  1. Group adult earthworms together according to their size. Size can be established by using the size chart on the General Earthworm Diagram to decide whether you have a small, medium or large adult. To determine the length of your earthworm, allow the worm to freely extend itself as if it was crawling. Measure the maximum distance the earthworm covers when completely stretched out. At no time should you manually stretch an earthworm - this kind of stress can severely damage an earthworm. Once size is established decide on the colour of the earthworm. Next, flip the worm over to expose its underside (ventral view). Look for the position of the clitellum to the head (some species have the clitellum very close to their heads) then examine the clitellum for genital tumescence (see figure 1) (GT) and the general pattern of the tubercula pubertatis (see figure 1) (TP) patterns.Be sure to use the on-line Taxonomic Key, Field Guide and Anatomy pages for more detailed information and instructions on how to identify your earthworms.
     
  2. Striped Worm
    Striped Worm
    Non-striped Worm
    Non-striped Worm
    Once size is established decide on the colour of the earthworm. When determining the colour of an earthworm, make sure that you are looking at the dorsal side (back side) of the earthworm. The ventral side of most earthworms is colourless, and thus cannot be used in identification. Pay particular attention to the colour between the head and the clitellum. This is where the majority of an earthwormís pigmentation occurs. Though most earthworms have a solid coloration, some are striped. In our key, Eisenia foetida is the only striped species. It has red segments, and yellow intersegmental furrows. Therefore, if you come across a striped earthworm, you likely have this species.
     
    Identifying earthworms
     
    Examining fine details is not necessary when using the key. Instead, use the Taxonomic Key to examine the pattern on the clitellum. What is important is determining whether or not they are on alternating segments, or are they on consecutive segments. Are all the GT located inside the clitellum, or are some found outside the clitellum? Are the TP shaped like triangles or bars? Do the TP run the length of the clitellum or are they shorter than the clitellum?
     
  3. Flip the worm over to expose its underside (ventral view). Look for the position of the clitellum to the head (some species have the clitellum very close to their heads) then examine the clitellum for genital tumescence (see figure 1) (GT) and the general pattern of the tubercula pubertatis (see figure 1) (TP) patterns. †Examining fine details is not necessary when using the key. Instead, use the Taxonomic Key to examine the pattern on the clitellum. What is important is determining whether or not they are on alternating segments, or are they on consecutive segments. Are all the GT located inside the clitellum, or are some found outside the clitellum? Are the TP shaped like triangles or bars? Do the TP run the length of the clitellum or are they shorter than the clitellum?
     
    Alternating GT GT on adjacent segments
    Alternating GT GT on adjacent segments

    For example: suppose you have a greenish tinged earthworm that you have collected from a muddy garden. Youíve checked its size by using the size chart on the General Earthworm Diagram to find that it is small or medium (as size of this species depends on habitat). You look on the underside of the clitellum and you see 3 pairs of small button-like (or sucker-like) GT along the fringe of the clitellum. You also notice that these button-like GT are arranged on alternating segments. On the Taxonomic Key, a greenish earthworm, with button-like GT, on alternating segments is an Allobophora chlorotica. Be sure to use the Taxonomic Key, Field Guide and Anatomy pages for more detailed information and instructions on how to identify your earthworms.

  4. Follow down the key as far as you can. Write the information (species name) on the Observation Form. After you have identified your adults, put one representative adult from each species you identified and any unknown species you found into separate containers or vials for preservation. When you have an earthworm you cannot identify, set aside one representative adult specimen in a vial supplied by Worm Watch, add some soil and put the lid on. Label the container as UNKNOWN #1 and fill in the Observation Form with the same information.
     
  5. Return all the other earthworms to the soil in which you found them. You may find other earthworms that look the same as UNKNOWN #1 at other locations. Remember to always call this adult UNKNOWN #1 on the Observation Forms and the bottle. Make sure you also record the site location on the container or vial too. Do not put earthworms from more than one site in the same vial or container. When you are done sampling, bring your representative specimens back to your home, lab or school, to be preserved. Do not leave earthworms in the containers or vials overnight without preserving them!!!
     

 
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David Suzuki Foundation Nature Canada University of Ottawa Wilfrid Laurier University