Critter Catalog

What do they look like?

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.

• Other Physical Features
• ectothermic
• bilateral symmetry

• Sexual Dimorphism
• female larger
• sexes shaped differently

• Range length

  3.0 to 30.0 mm

  0.12 to 1.18 in

Where do they live?

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.

• Biogeographic Regions
• nearctic
  • native
• palearctic
  • native
• oriental
  • native
• ethiopian
  • native
• neotropical
  • native
• australian
  • native

What kind of habitat do they need?

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.

• These animals are found in the following types of habitat
• temperate
• tropical
• terrestrial

• Terrestrial Biomes
• tundra
• taiga
• desert or dune
• chaparral
• forest
• rainforest
• scrub forest
• mountains

• Wetlands
• marsh
• swamp
• bog

How do they grow?

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.

How long do they live?

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.

How do they behave?

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.

• Key Behaviors
• diurnal
• nocturnal
• motile
• sedentary
• solitary

How do they communicate with each other?

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.

What do they eat?

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.

• Primary Diet
• carnivore

What eats them and how do they avoid being eaten?

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.

• Known Predators

  • predatory wasps
  • parasitic wasps
  • other spiders
  • insect-eating birds
  • beetles (eat the eggs)

What roles do they have in the ecosystem?

Orb-weavers are predators that are usually low in the food web. They eat insects but are in turn eaten by other predators.

Do they cause problems?

Orb-weaver spiders can bite, and are venomous, but none of them are known to be particularly dangerous to people.

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

How do they interact with us?

Orb-weavers, like most spiders, are important predators of pest insects.

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

Are they endangered?

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.

• IUCN Red List [Link]

  Not Evaluated

Some more information...

Charlotte, the spider in the book "Charlotte's Web," belonged to this family of spiders.

Contributors

George Hammond (author), Animal Diversity Web.