Spiders of the World

Identifying Spider Families

Dr Gillespie writes:

"Before you can say anything about species, and evolution, you have to identify the spiders using diagnostic characteristics. You can often get a pretty good idea of which spider is which by looking at the shape of their abdomen, the type of web they spin or the way in which they walk. Identifications always have to be confirmed by looking at the spiders using a hand lens or a microscope, and seeing how the eyes are arranged, how many claws it has, what its genitalia look like, etc."

"As I mentioned, the spiders in Hawai`i belong to a few groups whose ancestors got here and radiated into swarms of closely related species when they found no other spiders occupying the diverse array of habitats that Hawai`i has. The Tetragnatha spiders, for example, formed species in all sorts of habitats, and formed 'ecological equivalents' to species on the mainland that are quite unrelated. So, if you're looking around a similar area on the mainland, you see similar looking spiders, but they are from lots of different families."

A spider's body has two parts, a cephalothorax, consisting of the head and the thorax, and the abdomen. These two parts are joined by a short, thin stalk, or pedicel. Four pairs of legs are attached to the cephalothorax, as are the jaws, or chelicerae, ending in fangs. Also attached to the cephalothorax are small leg-like appendages called the pedipalps. Male spiders have clubs at the end of the pedipalps; females do not. Most spiders have eight eyes at the front of the cephalothorax -- but some have fewer, and others have none.

On the rear underside of the abdomen, most spiders have six finger-like structures, called spinnerets, which they use to spin silk.

To identify the family that a spider belongs to, you need to consider several key diagnostic features. Important features for each of 17 families of spiders are given in the Spider Family Key as well as on Master 1.5g "Spider Family Key" in the JASON VI Curriculum. The diagnostic features to consider are:

1. Web
   Is the spider in a web? If so, is it a standard web with fine, sticky strands, or a cribellate web made up of hackled threads, like fine wool? What can you say about the shape of the web? Is it an orb web with spirals supported by lines which radiate out from the center? Is it dome-shaped or funnel-shaped?
2. Morphological Characteristics (Appearance)
   How large is the spider? How are the eyes arranged? What do the legs look like? How does it compare with the descriptions given in the Spider Family Key?
3. Behavioral Characteristics
   Behavior is often difficult to observe. How does the spider move, hunt, etc.?

Spiders of the World

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Gene Carl Feldman (gene@seawifs.gsfc.nasa.gov) (301) 286-9428
Todd Carlo Viola, JASON Foundation for Education (todd@jason.org)