Interactive Key to the World Genera of Cobweb Spiders (Theridiidae)

Key to Genera of Cobweb Spiders Lucid key

Key to Genera of Cobweb Spiders Lucid key

Version 1.0beta

Updated January 28 2003. Upgraded into Lucid v4 December 2020.

This is an early trial version of this interactive key, still lacking many images and most notes. Although it almost certainly contains some errors at this point, it nevertheless has proved fast and efficient in trial runs, even for people with little experience identifying spiders. It includes all currently valid theridiid genera (all included by Platnick, 2002).

Please send any error reports or other comments to Ingi Agnarsson (email: This key is non-commercial and use of this key is free for anyone. However, data and images may not be copied or reproduced without permission from the Author. If you use this key, or information from it, for your work you are asked to cite it as follows:

Agnarsson, I. 2003. Interactive Key to the World Genera of Cobweb Spiders (Theridiidae), version 1.0 beta.

How to use this key

In many cases using the ‘Best’ command of Lucid is the most efficient to go through the key. However, if your specimen has some striking features, such as carapace protrusions, abdominal scuta, striking coloration etc you may be able to identify it faster, or even instantly, by first seeking for the characters that describe these conditions. It is furthermore useful to be aware of some key theridiid characters. The presence/absence of a colulus, and its form, for instance is very important for identification. To speed up your identification and avoid confusion, you may also want to get rid of taxa that you are very unlikely to ever collect (due to their extreme rarity). This may be done by selecting under a character named: ‘Monotypic and/or very rare genera’. This is a key to the world genera of Cobweb spider, but you can quickly turn it into a regional key by selecting e.g. N-America under the character ‘distribution’. Larger regions may be selected by e.g. choosing N, S and Central America at the same time, and then it becomes a key of the Theridiid genera of the New World. Limiting the region dramatically increases the speed of identification. You should keep in mind, however, that the exact distribution of many genera is not well known, and especially when collecting in poorly known places (practically anywhere but N-America and Europe) you may want to consider all described genera. Finally, you should always double check the genus ID Lucid suggests by comparing your specimens to generic descriptions. Although I have found the key to be efficient, there are still errors in the keys, and furthermore, a minor overlook by the observer may mislead the program. Ultimately descriptions and images of all genera will be associated with this key, but until then Levi & Levi’s (1962) ‘The genera of the Spider Family Theridiidae) is the most comprehensive resource.


Ingi Agnarsson