DMNS-Colorado Spider Survey

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Dichotomous Key
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A dichotomous key is arranged as paired couplets. With the specimen in front of you (and some means of magnifying the specimen), read through the first couplet designated 1a and 1b. If all the characteristics of 1a better describe your specimen, then proceed to the couplet number indicated at the end of the line. If the characteristics listed under 1b better describe the specimen, then proceed to a different couplet indicated at the end of that line. Continue in this manner until you are led to a family name. Some of the characters in the key refer to web characteristics, behavioral characteristics, or to the habitat in which the spider was found. Therefore, it is a good idea to take note (a literal note or a mental note) of these traits for the different specimens you collect. It is useful to carry a field notebook with you for such purposes.

Roman numerals are used to indicate a particular leg. Leg I is the leg nearest the eyes while Leg IV is the leg nearest the abdomen. The word anterior means closer to the cephalothorax while posterior means closer to the spinnerets. The word dorsal means on the top side of the animal while the word ventral refers to the "belly" side.

Dichotomous Key to the
Common Families of Colorado Spiders
(derived from Kaston, B.J. 1978. How to Know the Spiders. The Pictured Key Nature Series, Wm. C. Brown Co. Publishers, Dubuque, Iowa.)

Parallel fangs and rastellum on the chelicerae of mygalomorph spiders. Fangs on the chelicerae of labidogath spiders.		1a) Suborder Orthognatha or Mygalomorpha Fangs, or chelicerae, move more or less parallel to one another (Fig. 8). Two pairs of lungs evident as slit-like structures on the ventral surface of the abdomen. Fairly large, robust "tarantula" spiders. These spiders will only be found in the southern portion of the state. 2 1b) Suborder Labidognatha Chelicerae move in opposition (Fig. 9). Most spiders encountered in Colorado will fall into this Suborder. 3

Claw tufts and scopula of a tarantula.		2a ) CTENIZIDAE (Trapdoor spiders) Tarsi with two large lateral, or side, claws on the tarsi and one small median, or middle, claw. No claw tufts evident. A rastellum (see Fig. 8) evident on the chelicerae. Spiders are usually found in burrows hinged with a lid made from soil and lined with silk (as is the burrow). The trapdoor is often very well camouflaged with bits of leaves and other material. Males often wander outside the burrows after heavy rains from November to February. 2b) THERAPHOSIDAE (Hairy mygalomorphs or Tarantulas) Spider covered with hairs. Tarsi with claw tufts and scopula (Fig. 10). Without rastellum on the chelicerae. Mostly active at night. Males often wander in search of females from July to November.

Cribellum anterior to the spinnerets on a cribellate spider. The calamistrum is used for drawing silk out of the cribellum.		3a ) Cribellate Spiders A specialized spinning plate, called a cribellum (Fig. 11) is located anterior to the spinnerets in females and juveniles. A specialized comb of bristles, called a calamistrum (Fig 12) is located on metatarsus IV of females and juveniles. Remnants of the cribellum or the calamistrum can sometimes be seen on adult males. Webs of these spiders often have a bluish sheen. 4 3b) Ecribellate Spiders Spider lacks both the cribellum and the calamistrum. 9

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