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Theridiidae

What do they look like?

All spiders have two body segments, a cephalothorax in front and an abdomen behind. In this group the abdomen is often very round. 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, and in mating, and are much bigger in male spiders than in females.

Cobweb weavers have eight eyes on the front of their cephalothorax, arranged in two rows of four. Below the eyes is the mouth and fangs that they use to bite their prey with. They all have venom to paralyze and digest their prey.

Female cobweb weavers are often much bigger than males. There is a lot of variation in color in this family, but many species are brownish-grey with various patterns of darker marks.

One important group of cobweb weavers in the widow spiders. They are one of the few groups of spiders whose venom can hurt people. Only female widow spiders bite. They are shiny black, and have red markings on the bottom of their round abdomen.

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    2.0 to 15.0 mm
    0.08 to 0.59 in

Where do they live?

This is a large and diverse family of spiders, with thousands of species found all over the world. In Michigan there are several dozens species at least, and probably more still unknown to science.

What kind of habitat do they need?

These spiders live in many different kinds of habitats, on the ground, on plants, in burrows and caves, pretty much anywhere they can spin their webs. They often build in dark, sheltered places, in piles of branches or basement corners. Some species in this group are common house spiders.

How do they grow?

Spiders hatch from eggs, and 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, which they do many times during their lives.

How do they reproduce?

Male cobweb weavers leave their webs and go looking for females. If they find one, they approach very cautiously, because sometimes females eat the males.

Female cobweb weavers lay eggs. They produce clutches of upto to 250 eggs at a time, and place them in egg sacks made of brownish silk. They hang the egg sacks in their web and guard them. In some species the female also feeds her babies after they hatch. They get digested food from her until they have grown enough to shed their skin the first time. After they shed they go off on their own. This is unusual, no other family of spiders is known to feed their offspring.

How long do they live?

Male cobweb spiders rarely live more than a year, but in some species females can live for three years or more.

How do they behave?

Spiders in this family are usually more active at night. That's when they work on their webs and are ready to catch prey. During daylight they hide from predators. A few species wander in search of prey and don't use a web.

Nearly all species in this family are solitary. They only come together to mate. However, a few species in West Africa are social. They build large webs together, and cooperate to catch and eat large insects and other prey.

How do they communicate with each other?

Like all spiders, cobweb weavers are sensitive to vibrations and touch. They probably also use chemical sense to communicate, and they can see, but not too well. Some species in this family have special body parts they can rub together to make noise or vibrations. No one knows exactly what they are for.

What do they eat?

These spiders eat insects and other invertebrates. Some build nests that can trap flying insects, others stick lines down to the ground that snap up and pull prey into the web. A few species sneak into the webs of other spiders and steal their prey. When cobweb weavers catch a prey animal, they wrap it in sticky silk and bite it, injecting venom that paralyzes or kills the prey. They sometimes leave the prey wrapped up and hanging in the web and eat it later. No other family uses sticky silk to wrap their prey, they just use regular silk that doesn't have glue on it.

  • Primary Diet
  • carnivore
    • eats non-insect arthropods

What eats them and how do they avoid being eaten?

These spiders rely on camouflage colors to avoid predators. They also sometimes build a special hiding place in their webs. Some species put bits of soil or plant parts in their web to hide it. The few species with strong venom have warning colors and will bite if threatened.

Do they cause problems?

Some people don't like to have these spiders making cobwebs in their house. Also, a few species can give people a dangerous bite.

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

How do they interact with us?

This family of spiders includes lots of species that eat insects in agricultural fields. They are important in controlling pest insects.

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

Are they endangered?

No species in this family are known to be in danger of extinction.

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

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. "Theridiidae" (On-line), Animal Diversity Web. Accessed December 07, 2016 at http://www.biokids.umich.edu/accounts/Theridiidae/

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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