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Leeches are cards that you keep forgetting. Because they require so many reviews, they take up a lot more of your time, compared to other cards. Anki can help you identify leeches. Each time a review card “lapses” (is failed while it is in review mode), a counter increases. When this counter reaches 8, Anki tags the note as a leech and suspends the card. The threshold, and whether to suspend or not, can be adjusted in the deck options. If you keep failing that card, Anki will continue to alert you about the leech periodically. These warnings occur at half the initial leech threshold. For example, if you set the warning at 8 lapses, future warnings will happen every 4 lapses (at 12, 16, and so on). Once a leech is found, there are several ways to handle it.

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Editing

The most efficient method to deal with leeches is to change how the information is presented. Maybe your cards have too much information, or you’re trying to memorize something without fully understanding it. Often, it helps to follow the 20 rules of formulating knowledge, proposed by Dr Piotr Wozniak, the creator of SuperMemo. Some cards can benefit from a mnemonic. Even some well-written cards may need a boost in coherence, e.g. by adding cards for related concepts. However, it takes a lot of experience to know how to formulate the material properly, break it down into smallest possible components, and use mnemonic techniques.

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Deleting

If the material you’re struggling with isn’t important enough to justify the time spent, you can simply delete the card. By selectively deleting difficult and obscure items, you can spend more time learning other material, making studying more enjoyable. If you think the card might be useful for future reference, you can leave it suspended.

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Waiting

Some leeches are caused by “interference”. For example, an English learner may have recently learned the words “disappoint” and “disappear”. As they look similar, the learner may find themselves confusing the two when trying to answer. In such situations, it’s often helpful to concentrate on one idea at a time. Once that idea is firmly ingrained in your mind, you can then start learning the other idea. So, in these situations, you might want to leave one of the words suspended until you have learned the other one well, and then unsuspend it. For a more detailed discussion, you can refer to the article “Dealing with Leeches”, written by Soren Bjornstad.