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Local animals in this group:

Thomisidae

What do they look like?

Crab Spiders usually have short, wide, flat bodies. The first two pairs of legs are larger than the back legs, and are usually held open so that the spider can easily grab its prey. They usually walk sideways or backwards, and use just their back legs. This is where they get their name.

All crab spiders have eight eyes, and the eyes on the edges of their cephalothorax are often raised up on bumps, so they can see in all directions. These spiders have small fangs compared to other spiders, but their venom acts quickly to paralyze their prey.

In some species males and females are different colors, and males are often much smaller than females. Crab spiders usually are colored to match their habitat. Some species can slowly (over a period of days) change color to match the color of the flowers they are hiding on.

  • Sexual Dimorphism
  • sexes alike
  • female larger

Where do they live?

There are over 2,000 species of crab spiders and they are found all over the world. In North America there are over 200 species.

What kind of habitat do they need?

Spiders in this group can be found in just about any habitat where they can hide, adn there are insects to eat. The only places they can't live are the dryest deserts or the coldest mountaintops.

How do they grow?

Females lay eggs. The spiderlings that hatch out look like mini-adults. As they grow they have to shed their skins, but they do not change their general shape.

How long do they live?

In cold climates the adults of this species usually die when winter comes, so probably live one year or less. In tropical climates they may live longer.

How do they behave?

These spiders live and hunt alone. They are usually active during the day. Some species stay in the same place for a long time, attacking prey that comes by. Other species roam around looking for prey.

How do they communicate with each other?

We don't know very much about how these spiders communicate. They probably use sight, touch, and smell.

What do they eat?

Crab spiders ambush their prey, mainly insects, sometimes holding still and relying on their camouflage to keep them from being seen by their prey, sometimes running quickly. When a prey animal is close enough, they grab it with their strong front legs and bite it quickly.

  • Primary Diet
  • carnivore
    • eats non-insect arthropods

What eats them and how do they avoid being eaten?

Crab spiders' main defense is their camouflage. They will hide or drop away from predators if they can. They can bite other invertebrates, but this doesn't work against vertebrate predators.

Do they cause problems?

These spiders can bite, but are not aggressive, and are not dangerous to people. They sometimes eat beneficial insects like honeybees that pollinate crops, but they eat enough pests that this is not usually a problem.

  • Ways that these animals might be a problem for humans
  • injures humans
    • bites or stings

How do they interact with us?

Crab spiders eat lots of insects and mites that are pests. They are often a big help to farmers, because they hunt on plants and eat the invertebrates they find there.

  • Ways that people benefit from these animals:
  • controls pest population

Are they endangered?

No crab spiders are known to be endangered, but many species are still not known to science, and could be disappearing without anyone knowing.

  • IUCN Red List [Link]
    Not Evaluated
 
University of Michigan Museum of ZoologyNational Science Foundation

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. "Thomisidae" (On-line), Animal Diversity Web. Accessed September 21, 2014 at http://www.biokids.umich.edu/accounts/Thomisidae/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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