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Kentucky spiders Crab Spider
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Crab Spider CRAB SPIDERS
& RUNNING CRAB SPIDERS

Critter Files/Spiders/Crab Spiders & Running Crab Spiders
By Blake Newton
University of Kentucky Department of Entomology
   
 
TAXONOMY

KINGDOM: Animalia | PHYLUM: Arthropoda | CLASS: Arachnida | ORDER: Araneae | FAMILY: Thomisidae (crab spiders) & Philodromidae (running crab spiders)

 
Other Names: Thomisids (crab spiders), Philodromids (running crab spiders)
 

WHAT IS A CRAB SPIDER?
LIFE CYCLE
ECOLOGY
PEST STATUS
COMMON KENTUCKY CRAB SPIDERS
COLLECTING & PHOTOGRAPHY
CRAB SPIDER FACTS
MYTHS, LEGENDS, AND FOLKLORE

 
WHAT IS A CRAB SPIDER?

There are several types of spiders that are commonly called "Crab Spiders."  The most commonly encountered crab spiders found in Kentucky are in the family Thomisidae.  These are often called "thomisid" crab spiders, or simply "thomsids."  Thomisids tend to have a flat shape compared to other spiders, and their front two pairs of legs are typically very long compared to the back two pairs.  Thomisid crab spiders hold their front legs out and up, similar to the way a crab holds its claws.  Many thomisid crab spiders have bright, "neon" colors (yellow, green, and orange).  Others have gray and brown color patterns.

 
Running Crab Spiders belong to the family Philodromidae.  They are sometimes called "philodromid crab spiders" and they are distinguished from thomisid crab spiders by their 2nd pair of legs, which are always longer than the 1st, 3rd, and 4th pair.
 
All crab spiders have eight eyes.  Like all spiders, crab spiders have eight legs, two body parts (abdomen and cephalothorax), and fang-like mouthparts called "chelicerae."
 
Typical crab spider. Note long 1st and 2nd legs.
Typical thomisid crab spider. Note the long
1st and 2nd legs. (R. Bessin, 2000)
SIZE: Body length up to about 1/2"
 
LIFE CYCLE

Like all spiders, crab spiders go through a simple metamorphosis.  Young crab spiders hatch from eggs and look like tiny adults.  They shed their skin as they grow.  Most crab spiders live for less than one year and have only one generation per year.  In most of these species, the females produce eggs in the fall, and the offspring hatch in the spring.  In other species, several generations of females produce young each year and immature larvae are the overwintering stage (thanks to Dr. Gary Dodson from Ball State University for this information). 

 
ECOLOGY

Most crab spiders and running crab spiders do not rely on silk to capture prey.  Instead, they are ambush predators: crab spiders wait motionless on flowers, leaves, and other strategic places for flies, bees, and similar prey.  Many crab spider species, especially in the family Thomisidae, have the same bright colors as the flowers on which they sit.  Other crab spiders have dark colors that blend well with bark or soil.  Crab spiders are able to walk forwards, backwards, and sideways with ease.

 
Flower spider feeding on a fly
Flower spider feeding on a fly (B. Newton, 2006)
 
PEST STATUS

Crab spiders are considered beneficial to humans.  Although they eat a few bees, they also kill flies, mosquitoes, moths, and other insect pests.  Some species are large enough to bite people, but no crab spiders are known to be dangerous.

 
COMMON KENTUCKY CRAB SPIDERS

FLOWER SPIDERS
FAMILY: Thomisidae | GENERA: Misumenops, Misumenoides, Misumena, others
Flower Spiders may be the most commonly encountered crab spiders in Kentucky.  Flower spiders have bright colors which allow them to blend in with the flowers on which they wait for prey.  Some flower spiders are able to change color to become camouflaged on different kinds of flowers, although the color change may take a few days.  Pictured below is a flower spider from the Misumenops genus and three views of Misumenoides formosipes.  These and related crab spiders are commonly found on Kentucky wildflowers and flowering plants (like milkweed and Queen Anne's Lace).  Thanks to Dr. Gary Dodson from Ball State University for help with flower spider identifications, along with biological information about these genera.

 
Crab spider, Misumenops sp., hunting on milkweed
Flower spider, Misumenops sp., hunting on milkweed
(B. Newton, 2003)
Crab spider Misumenoides formosipes on Queen Anne's Lace
Misumenoides formosipes on Queen Anne's Lace
(B. Newton, 2003)
   
Crab spider Misumenoides formosipes on Ironweed
Misumenoides formosipes on Ironweed
(B. Newton, 2005)
Crab spider Misumenoides formosipes waiting for prey
Misumenoides formosipes waiting for prey
(B. Newton, 2003)
   

Xysticus and Coriarachne spp.
FAMILY: Thomisidae | GENUS: Xysticus and Coriarchne
Crab spiders in the Xysticus and Coriarachne genera, like the ones pictured below, resemble flower spiders except that they often have more subdued colors (like brown, black, and gray).  This is probably because crab spiders in these genera usually hunt on the ground or on bark (instead of in flowers) where dark colors are best for camouflage.

 
A crab spider in the Xysticus genus, guarding an eggsac (B. Newton, 2003)
A crab spider in the Xysticus genus, guarding an eggsac (B. Newton, 2003)
 
Crab spider, Coriarachne genus
Crab spider, Coriarachne genus (B. Newton, 2005)

Tmarus spp.
FAMILY: Thomisidae | GENUS: Tmarus
Crab spiders in the genus Tmarus are infrequently encountered in Kentucky and they don't look very much like the other crab spiders in Thomisidae.  Little is known about their biology.  The ones pictured below were less than 1/2" long.

 
Tmarus sp.
Tmarus sp. (B. Newton, 2004)
Tmarus sp.
Tmarus sp. (B. Newton, 2005)

RUNNING CRAB SPIDERS
FAMILY: Philodromidae
Running Crab Spiders belong to the family Philodromidae.  They are not encountered as often as crab spiders in the family Thomisidae, but they are common nevertheless.  Pictured below are running crab spiders from the genus Tibellus and Philodromus.

 
Running Crab Spider, Tibellus sp.
Running Crab Spider, Tibellus sp. (B. Newton, 2004)
 
Running Crab Spider, Philodromus sp.
Running Crab Spider, Philodromus sp. (B. Newton, 2005)
 
COLLECTING & PHOTOGRAPHY

Although crab spiders are fairly common, finding one might take some patience because they are often well camouflaged, especially the ones that live on the ground.  Crab spiders make great photography subjects, especially the brightly colored flower spiders.  Flower spiders are very common in garden flowers and in wildflowers.  If you want to find a flower spider, try to think like a flower spider: where would you sit if you wanted flies and bees to come to you?

 
CRAB SPIDER FACTS

Scientists think that the venom of certain crab spiders is more potent than that of most other spiders: this allows crab spiders to quickly paralyze the large and tough bees that often visit flowers.  However, crab spider venom is not known to be especially dangerous to humans.

Dr. Gary Dodson has been studying crab spider ecology at Ball State University in Indiana.  Among his findings: male crab spiders will sometimes feed on nectar.  Read more about his research at:
http://www.bsu.edu/web/gdodson/research.htm

The University of Nebraska Entomology website has some great pictures of crab spiders at: http://entomology.unl.edu/images/spiders/spiders3.htm

 
MYTHS - LEGENDS - FOLKLORE

Do you know any myths, legends, or folklore about crab spiders?  If so, let us know.

 

Original document: 25 May 2004
Last updated: 12 Jan 2007

Photos courtesy R. Bessin and B. Newton, University of Kentucky
The Kentucky Critter Files are maintained by Blake Newton, Department of Entomology, University of Kentucky.
Contact: blaken@uky.edu

   
University of Kentucky Entomology/Kentucky Critter Files/Kentucky Spiders/Crab Spiders