BioKIDS home

Kids' Inquiry of Diverse Species

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

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends.

carnivore

an animal that mainly eats meat

chaparral

mid-altitude coastal areas with mild, rainy winters and long, dry summers. Dominant plant types are dense, evergreen shrubs.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

marsh

marshes are wetland areas often dominated by grasses and reeds.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nomadic

generally wanders from place to place, usually within a well-defined range.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Climbing plants are also abundant. There is plenty of moisture and rain, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

taiga

this biome is characterized by large expanses of coniferous forest, there is an extended cold season and heavy snowfall.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

year-round breeding

breeding takes place throughout the year

 
University of Michigan Museum of ZoologyNational Science Foundation

BioKIDS home  |  Questions?  |  Animal Diversity Web  |  Cybertracker Tools

. "Thomisidae" (On-line), Animal Diversity Web. Accessed April 25, 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.
Copyright © 2002-2014, The Regents of the University of Michigan. All rights reserved.

University of Michigan