Friday, September 23, 2011

Crab spiders

 About the middle of September I was out walking and hunting insects as I often do and came across this beautiful crab spider. I have seen crab spiders before but this one seemed especially elegant and has inspired me to do some research on them.
Misumenoides formosipes

Crab Spider is a common name for a group of spiders that actually look a little like crabs and act like them as well. The first two pairs of legs are longer than the rest and are normally held out from the side like a crab. They walk forwards, backwards and sideways like those little fiddler crabs I see on most Atlantic beaches. They primarily use their third and forth pair of legs to walk.  But unlike those crabs that scurry about, these crab spiders sit and wait and wait and wait. They are masters of patience and camouflage. Besides being a good technique for not getting eaten up it is also a good strategy for attack.

The above Misumenops asperatus (Northern Crab Spider) is still very small.

Below are a couple example of where they hide.

I believe the spider hiding below is a Tan Crab Spider, Xysticus transversatus.
Xysticus ferox (Brown Crab Spider)

Some, such as a Misumena vatia, can actually change colors to match their surroundings but this usually takes a few days. Like I said they have patience.

Bees seem to be a favorite food and are easily captured while they are focused on searching for pollen. This is a Misumenoides formosipes and indicated by the prominent white ridge about and below the front row of eyes.

If I am actively searching for crab spiders they are pretty easy to see on the flower heads and among the petals but if I am just casually walking along what usually catches my eye is a bee or other insect that is in a weird posture and most importantly doesn’t fly off as I approach.

As you can see here a crab spider has grabbed a honey bee and injected its potent venom into the victim and is sipping away. Once they are feeding they are very reluctant to run and easily photographed. I spent about 5 minutes taking photos of this one and I was just about an inch away for most of the time. I even tested its patience by using my flash and it was not to be deterred.

Most of them are in the family Thomisidae and can also be referred to as “flower crab spiders” and the most common. I believe the one above is a Misumenoides formosipes. Please correct me if you know I am wrong or can identify any of the others. The

They don’t use their spinnerets to produce silk for webs but they do use it for drop lines for safe free falling.

Unlike Jumping Spiders and other hunting spiders they don’t have large eyes. The Thomisidae anterior and lateral eyes and posterior lateral eyes are closely placed and are mounted upon elevations that look a little like horns. Their eyes are small and work like motion detectors. They just wait in a prime spot until an unsuspecting insect lands nearby. Location, location, location is the name of the game and they usually pick the freshest flowers to rest on since these are the ones full of pollen and nectar that attract prey.

I think crab spiders are the easiest of all the spiders to find and photograph but for plain cuteness you can't beat a jumping spider. I will try to gather up some photos and information and feature them. Have fun searching while we still have flowers in bloom.


Jacqueline Donnelly said...

Thanks for the lesson on crab spiders. I found lots this summer, most of them because I first saw their prey dangling. Fascinating! I can't wait to see your jumping spider photos. We had one who lived in a window sill and I looked for it every day. Yes, it was really cute!

Anonymous said...

I learned about crab spiders the hard way. I'd put one of my hand reared Black Swallowtails out on a flower to nectar. Thought it was odd that it was still there nearly an hour later. Yep, a crab spider had made a meal by sucking out the body liquids. These spiders seem to have a knack for picking flowers that match their own color so they are nearly impossible to see.