All spiders have two body-segments, a cephalothorax in front and an abdomen behind. They have eight legs, all attached to the cephalothorax. On the front they have two small "mini-legs" called palps. These are used to grab prey. They are also used in mating. Palps are much bigger in male spiders than in females. All orbweavers have fangs that they use to bite their prey with. They all have venom glands that produce toxins. The toxins paralyze and digest their prey.
Orb-weavers are more diverse physically than the other groups of spiders. They usually have a fairly large abdomen, and it nearly always overlaps the back of the back edge of the cephalothorax. The shape of the abdomen varies a lot between species. Sometimes it is spiny, sometimes smooth, sometimes very irregular in shape. Nocturnal orb-weavers are usually brown or gray. Diurnal species are more brightly colored and may be black and yellow or orange. Often females are much larger than males in this group.
Orb-weaving spiders are found all around the world. There are over 4000 species known, and probably at least that many still unknown to science. In Michigan there are at least 40 species known, and probably more still out there.
Orb-weavers live anywhere there are insects and places to put up their webs. They are much more common in humid habitats than in dry ones.
Spiders hatch from eggs. The hatchlings look more or less like grown-up spiders, though sometimes their colors change as they age. To grow they have to shed their exoskeleton. They do this many times during their lives.
Adult Orb-weavers can't usually survive below-freezing weather, so they don't live for more than a year. In tropical regions with warm winters, they may live longer.
Sometimes males build small webs around the web of a female, perhaps living there while waiting for her to finish growing. Otherwise spiders in this family are not social, they each build their own web and stay with it. As noted above, some species hunt at night, others are active during the day.
Communication among orb-weavers is mostly by touch and web vibrations, though there are probably some chemical signals too. Their vision is not good enough for much visual communication.
These spiders catch and eat the insects they trap in their webs. When an insect touches the sticky web it gets caught. They spider quickly rushes in and starts spinning and wrapping the insect in more webbing to keep it trapped. The orb web is very distinctive, and is the easiest way to tell that a spider belongs to this group. Orb webs are flat, and have a neat spiral of sticky silk that goes around and around from the middle to the outer edge. Many species in this family build a new web every day or every night, and then take it down and eat it before hiding for the night or day.
Many orb-weavers only put up their webs at night, in order to avoid birds. Orb-weavers with webs up in daylight are more brightly colored, maybe to warn predators of their venomous bite. If disturbed in their webs, many orb-weavers quickly drop away.
Orb-weavers are predators that are usually low in the food web. They eat insects but are in turn eaten by other predators.
Orb-weaver spiders can bite, and are venomous, but none of them are known to be particularly dangerous to people.
Orb-weavers, like most spiders, are important predators of pest insects.
No orb-weavers are known to be endangered, but since many species are still not known to scientists, there could be rare ones out there we don't know about.
Charlotte, the spider in the book "Charlotte's Web," belonged to this family of spiders.
George Hammond (author), Animal Diversity Web.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
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.
living in the southern part of the New World. In other words, Central and South America.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
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.
a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.
an animal that mainly eats meat
mid-altitude coastal areas with mild, rainy winters and long, dry summers. Dominant plant types are dense, evergreen shrubs.
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.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
parental care is carried out by females
union of egg and spermatozoan
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
fertilization takes place within the female's body
marshes are wetland areas often dominated by grasses and reeds.
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
found in the oriental region of the world. In other words, India and southeast Asia.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
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 forests develop in areas that experience dry seasons.
breeding is confined to a particular season
remains in the same area
offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
this biome is characterized by large expanses of coniferous forest, there is an extended cold season and heavy snowfall.
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).
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
A terrestrial biome found in very cold places -- either close to polar regions or high on mountains. Part of the soil stays frozen all year. Few kinds of plants grow here, and these are low mats or shrubs not trees. The growing season is short.
breeding takes place throughout the year