spiders

A friend recently asked for some tips how to identify spiders.

jumping-spider-another1. Leg size and position

Often the length and position of the legs are easy to see and can give you a clue. Jumping spiders like this one have short legs that are tucked up under their bodies.

 

flower-spider

Crab spiders have 2 pairs of long front legs. They hold their front legs out to the side with the tips directed forward.

feather-legged-spider-1

Feather-legged spiders also have extra-long front legs. They hold their first pair of legs directly out front of themselves and pressed together.

wolf-spider-23Wolf spiders have legs that are all roughly the same length and shape, as do a few other groups such as fishing spiders.

2. Web pattern

Some spiders are easier to identify by their webs.

garden-spider-orbOrb weavers (also called garden spiders) produce large complex webs, often across paths.

funnel-web-retreatFunnel web spiders produce sheets of silk around a central, hollow retreat.

3. Eye Pattern

If you can get a good photograph from the front of the spider, the size and position of the eyes can aid in identification.

Let's take a quick look at spider anatomy, in case you are not sure which is the front end.

basic-spider-anatomy

Besides the legs, the other parts you see on the spider are the abdomen (body area covered with red arrows), and the combined head and thorax, called the cephalothorax (body area covered with yellow arrows). The two appendages that surround the mouth are the pedipalps. The pedipalps are at the front end of the spider, with the eyes.  (Note:  in newer scientific texts the abdomen may be called an opistosoma and the cephalothorax called a prosoma).

The eye patterns are distinctive and easy to recognize with a bit of practice.

jumping-spider-face-viewLooking face on at a jumping spider you can see they have two large eyes in the front of their cephalolthorax and two smaller eyes on either side.

jumping-spider-side-view-general

They also have two smaller pairs of eyes further back. See the dark, shiny eye about 1/2 way back on the cephalothorax?

crab-spider-on-purple-100In contrast, the crab spiders have a cluster of tiny eyes right in a oval at the top and front. The eyes in this spider are set into the orange-yellow colored area. You can hardly see the eyes in comparison with those of the jumping spider.

Eye_Arrangement_of_a_Wolf_Spider

(Photograph by Thomas Shahan from USA licensed under the Creative Commons Attribution 2.0 Generic license at Wikimedia.)

Wolf spiders also have two large central eyes, but have a downward-curving row of four eyes below them. They also have another pair further back, which you can just see as a dark curves.

This is only a very basic introduction to spider identification. If you would like to learn more about this, BugGuide has set up an excellent page showing all the different eye patterns in spiders.

Spiders have quite a bit going on and are actually quite fascinating once you get to know more about them.

We haven't had a spider lately for Bug of the Week.

crab-spider-face

How about a crab spider waiting for a meal?

crab-spider-on-purple-100

Crab spiders are known for using camouflage. In fact, adult female crab spiders have been shown to be able to change color to match the color of the flower they are sitting on.

So, why isn't this crab spider purple, or sitting on a white or yellow flower? Isn't being white going to wreck its chances of catching prey?

As this article from Wired points out, color matching does not necessarily help the spider to catch prey. One reason may be because bees can see ultraviolet light. Some spiders may reflect ultraviolet light, so even though the crab spiders look like they are matching the flower to our eyes, to the bees they stand out against their background.

This video suggests that standing out against the background may attract prey rather than dissuade it (it also shows crab spiders hunting).

Why would bees be attracted? The video does not explain this, but flowers have patches of ultraviolet that serve as beacons to the nectar. These patches are contrasting, and are thought to act like "signposts" directing the bees to the good stuff. Crab spiders may be trying to change the signs to direct flies and bees to themselves instead.

Now we are back to the question, why do female crab spiders change colors to match the flowers as we see them? Do you have any ideas?

1 Comment

Today I thought I'd dig through the archives and find you a very tricky mystery insect.

mystery-insect-2014

Do you have any guesses what it might be? (I know the photograph isn't the best.)

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In case you were wondering about the insects in last week's post, here are their identities and links to the original posts.

2013-spring-fuzzy-bee-better

This fuzzy little bee is a digger bee, probably genus Centris. It is a type of solitary bee, which means each female digs and provisions her own nest. (Spring is in the air)

2013-checkered-white-adult

This dainty butterfly is a checkered white.

butterfly-on-foot

On my toe is a tropical butterfly I saw during a visit to Butterfly Magic at the Tucson Botanical Garden. It is a brown clipper, Parthenos sylvia. There is also a blue form.

2013-first-monarch-in-yard

We were excited to see the first monarch butterfly of the fall.

2013-hasy-moth

I gave the tiny owlet moth with the rainbow of colors on its wings a second look.

stripy-face-better

Who can resist a photograph of a queen butterfly caterpillar?

2013-asparagus-beetle

I knew the plant was a naturalized asparagus plant when I saw the spotted asparagus beetle.

2013-locust-borer

A sign of fall in the East, this is a locust borer beetle.

2013-jumping-spider

The tiny guy with the big eyes is a jumping spider. You can see more here at this older post.

Thank you for playing!