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Crafty crab spider uses a form of magic

crab spider and bee

Hidden crab spider has managed to grab this unfortunate bee visiting an echinecea. Note how the pinkish stripe on the side of the spider neatly matches the colour of the flower. Donald McClure photo

A visitor to most County gardens in summer is the crafty and elusive crab spider.  Not that I am a particular admirer of this creature, but I am fascinated by its ability to make its living by blending into its surroundings and using a little magic.

That bit of trickery centres around this spider’s unique ability to transform it colours to blend in with the its background  to aid in its survival and provide a tactical advantage over other small creatures which it hunts.

This stealthy little guy is spotted in bright purple to match his spring hiding place while he waits for unsuspecting flies to visit. Donald McClure photo

These interesting creatures used to be quite plentiful in our area. You would commonly find them lurking behind flower petals and stems in almost every type of perennial.  Today they are still there — but it seems to me in much shorter supply and often take some hunting to discover.

I am not sure why its numbers have dropped over the last two summers. But it cannot be explained away by pesticide sprays — because we never use these sprays on our property.

This term crab spider refers to this creature’s use  of broad clutching forelegs and a crab-like scudder which are remindful of a conventional crab’s  machinations as its hunts its prey from stealth.  Many can move backwards or sideways — just like real crabs. These spiders were not designed to spin a web like a normal spider. They are hunters. Their technique is to lie low in the shelter of a flower petal or stem and pounce on unsuspecting insects visiting the flower to collect nectar.

Crab spiders have a devastating venom that immobilizes their prey.  Combine this with their powerful front arms and they overcome insects two or three times their size.  We do know that all crab spiders have eight eyes.  Like all spiders, crab spiders have eight legs, two body parts (abdomen and cephalothorax), and fang-like mouthparts called “chelicerae”.

We also know that the females of the species are the most aggressive and protective. There are more than 2,000 varieties in the world with 200 living in North America. Science is now acknowledging that some varieties (and possible only the females) are able to change their colours to blend in with backgrounds. How they do this we have some ideas but according to the US National Library of Medicine “the change of colour is based on a complex physiological process that we no not understand.”

One species — the goldenrod crab spider (common in Alberta) is completely yellow when sitting on a goldenrod flower, but can change its colour to white when on a daisy. According to recent reports the white-bodied spider can seemingly produce a yellow liquid pigment in its skin when on a yellow flower.  It makes it nearly invisible. It can later excrete the pigment to return to a white colour.

Evidently it takes the spider twice as long to produce yellow pigment and turn yellow than it does for it to turn white.

Crab spiders are considered by some to be beneficial bugs because they capture many insect pest species like flies and mites.  However according to a recent survey crabs seem to capture about 3.5 percent of all the bugs that visit the  host flower and unfortunately from my standpoint many of their victims are insects that help in pollination — like small bees.

Be careful when handling flowers in the garden.  Crab spiders are people shy and will flee and hide to avoid us. Their bite is not harmful to humans, but not pleasant.   We recommend that they should not be picked up with bare hands.

It was a few years ago that the late, great George Elliott (the master of macro photography of insects) asked me to do an article for his publication on the subject of crab spiders because I had some evidence that their was a possibility that they might be able to change their colour so that they could blend into the background of any flower they visited.

Today we are offering a number of pictures taken in our garden which seems to give support to this idea.

Fiesty little guy has almost matched his habiliments to the bright red hue of this lily. Donald McClure photo

Yellow crab

This jaunty little crab spider has come up with a perfect concealment strategy in this lily, mimicking the reddish-brown spots almost to perfection in the summer garden. Donald McClure photo

Filed Under: Donald McClureUncategorized

About the Author: He can tickle your funny bone or tug at your heart strings. County people may know him as a chronicler of everything that happens (or should happen) in the garden, but his interests stretch across the natural world. His unique sense of observation takes in a wide expanse of living and may even point out some truths about our own condition as managers of the world around us. With Loyalist antecedents in his family tree his roots go deep into the Ontario countryside.

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  1. Donald says:

    Thank you Louisa! Enjoyed your comments. Spiders are not high on everyone’s popularity list. But they are part of the scheme of things and they do achieve some useful and beneficial results. They also seem to be incredibly smart sometimes. And as you so elegantly describe — their webs do add a certain glistening mystique to out countryside. Best wishes Donald

  2. Louisa says:

    Donald, aren’t there so many spiders out there at the moment? They’re stringing themselves across my steps to try to snag me as I leave for work in the morning; they’re in my car; and on particularly dewy mornings, hundreds – thousands – of pearly webs are glistening in the fields in the sunlight! Makes me wonder, are they all getting the food they need?

    You’ve presented some gorgeous photos here with our leggy little friends. Makes them seem so nice and friendly and all. Well, except the first one feasting on the bee. But as I always say, Everybody’s gotta eat!

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