Crab Spiders: Thomisidae

Crab spiders, (family Thomisidae) get their name from their appearance and their movement patterns.

Typically the crab spider has a round body with short legs, resembling a crab. Like crabs, they also move from side to side.

Often crab spiders get the nickname flower spiders, however the name is not applicable to all Thomisidae.

• Genus Coriarachne
• Genus Ozyptila
• Genus Synema
• Genus Tmarus
• Genus Diaea
• Genus Bassaniana: The Bassaniana genus also goes by the name of bark spiders because of their habit of living under tree bark. Generally they share the physical characteristics of having dark cephalothorax and a lighter, patterned abdomen. The top picture shows a Bassaniana versicolor (tentative identification). It measures less than one-half inch in length, including the length of the front legs (the picture is enlarged for highlighting purposes).
• The name flower spider formally applies to the Goldenrod Crab Spider (Misumena vatia). Females are typically three times larger and consequently receive more noticed than the male. They normally have either yellow or white bodies with a stripe around the abdomen.
• Picture three, the Whitebanded Crab Spider (Misumenoides formosipes) highlights the fact that color name does not always apply. Apart from the eye pattern. the stripes on the top of the head portion of the body and the symmetrical pattern on the abdomen are good field identification marks.

  The body color and pattern for females can be yellow and red, as in the top picture, or yellow and black, white and black or white and red.

  Males are significantly smaller and often two sets of very dark front legs.

• Misumenops, also called the Hairy Crab Spider often have a white or yellow body. They somewhat resemble the whitebanded crab spiders, however their bodies are hairy.
• The Xysticus genus, often called ground crab spiders because of their propensity to hunt near the ground. Most Xysticus have a brown, beige or reddish color body, with or without an abdominal pattern.

Only three of those genera, Misumena, Misumenoides and Misumenops, commonly sit on flowers, hunting their prey.

No crab spider builds a webs, rather they rely on their small size and color to hide on either flowers or plants (depending on their body color) waiting for their potential prey to visit. The duller color species sit close to the ground or on bark or branches.

Identifying crab spider species, at least to the level of genus, can be done by close observation of some physical characteristics, including eye patterns. Many hunt on flowers and shrubs in residential areas, making them easy to find.

The links in the box point to articles profiling crab spider genera, and provide some general rules of thumb for differentiating the very similar Misumena, Misumenoides and Misumenops.

© 2005-2013 Patricia A. Michaels