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We've never discussed arachnids in detail here at Bug of the Week. Let's find out what we've been missing.

Spiders and their relatives belong to the class Arachnida. How can you tell whether a creature belongs to this group? Arachnids have two body regions called the prosoma (part with eyes and legs) and opisthosoma (rear section). Arachnids have eight legs and they do not have antennae, although they do have two short appendages in front called pedipalps that sometimes may be mistaken for antennae.

wolf-spider-1

Although almost anyone can recognize a spider, there are a number of related arachnids that are less well known.

Scorpions (Order Scorpiones)

scorpion-anatomy

Scorpions have are pincer-like pedipalps  and their opisthosoma is elongated into a relatively thick tail with a stinger on the end.

Like most other arachnids, scorpions are nocturnal. They come out at night to catch insects and other arthropods.

Related posts:

Psuedoscorpions

(Public domain photograph by Alex Wild)

These tiny creatures have pinchers like scorpions (red in this photograph), but have no tail and no stinger. They are often found in compost heaps where they feed on even smaller insects and mites.

Wind Scorpions or Sunspiders

sunspider1These desert arachnids have large chelicerae or jaws that they use for catching insects. They can also use their jaws to stridulate, or make a noise. They don't have a tail.

Related post:  Sunspiders

Whip Scorpion or Vinegaroon

giant-vinegaroon

Unlike all other arachnids, the whip scorpions have a thin tail at the end of the opisthosoma. The pedipalps are robust. In contrast the first pair of legs are thin and have a sensory function similar to antennae.

Vinegaroons have vinegar in their names because they can spray high concentrations of acetic acid if threatened.

Never seen one before? BBC Earth Unplugged has a video of one spraying.

 

Mites and Ticks (Order Acarina)

mite-red-closeThe two body regions are difficult to see in mites and ticks. Their bodies are unsegmented, like small blobs. Also, their legs tend to be quite short relative to their body size.

Certain kinds of mites are among the few arachnids that feed on plants. The red mite in the photograph is an insect predator.

Daddy Long-legs or Harvestman (Order Opiliones)

daddy-long-legLike the mites, the harvestman have what looks like a single oval body region. Unlike the mites, they have long thread-like legs.

Harvestmen differ from spiders by possessing fewer eyes, having only two rather than six or eight. They also lack both venom and silk glands.

Some species of harvestmen are omnivores or scavengers rather than true predators.

Want to learn more?

A few spider identification basics

Check out our growing list of children's books about spiders

spider-books-for-kids

What would you like to know about arachnids?

"Bugs" are in the news this month.

First of all, Gregory Vogt stopped by to let us know how the Spiders in Space were doing:

"The spiders made it to orbit Monday morning. The Space Shuttle Endeavour will rendezvous and dock with the International Space Station Wednesday morning. The spiders will be unstowed from Endeavour and transferred to the station Thursday morning. We should have the first pictures available for viewing by the weekend. Check out http://www.bioedonline.org."

Should be interesting to see how the spiders do in space.

Periodical cicadas are also in the news. There is a large emergence of thirteen year cicadas, Magicicada tredecim, across the southeastern United States right now. They are called thirteen year cicadas because they stay underground as nymphs for thirteen years.

Have you ever seen an adult cicada emerge? Here is a time lapse video that shows the process.

Edit: At the request of readers, I have removed the video because of the noise. You can watch it at Mark Dolies' link.

Video by Mark Dolejs (click the link to see how he made the video).

BugGuide has some good still photographs and more information.

Related posts:
Summer Sounds
Every Seventeen Years at Stop the Ride

Have you ever seen/heard periodical cicadas?