Monday, May 18, 2015

Watch Where You Stick Your Nose

I am visiting with my parents at the moment, enjoying my time in the upper Gatineau. I went outside to photograph the flowers of a Brassica sp (mustard), which came out rather well:

Brassica sp. with an insect visitor
The genus Brassica (mustard) is member of an economically important family, the Brassicaceae (crucifers or cabbage family). This family is the source of quite a lot of our food, including some familiar ones such as mustard & mustard greens of course, as well as broccoli, cabbage, cauliflower, turnip, Chinese cabbage, radish, horseradish, stock, and even rapeseed (source of canola oil).

Brassica sp.
Pieris rapae, the cabbage white butterfly, which I mentioned having seen in Montreal recently, is one of the major predators of this particular family and is often considered a pest on farms where Brassicaceae are being grown.

So did you notice anything odd about that last photo?

If you didn't (and you probably didn't, be honest with yourself), then you are excellent proof of the effectiveness of the camouflage of Misumena vatia (goldenrod crab spider). If you look closely, you can see the legs of this spider, one extending beyond the stamens of the top left flower, and two more below that flower. Here's a better shot of M. vatia:

Misumena vatia on Brassica sp.
Even in this one, you might miss the spider if you're not looking too closely. But she's hanging off the underside of the flower on the left.

I say she, and I know she, because individuals with yellow legs and of this size must be the females; the males are much smaller with brown legs.

Misumena vatia on Brassica sp.
Apparently the female of this species is able to change colour (though it takes a matter of weeks, not moments) between yellow and white, so they can be found on white flowers as well as yellow ones.

This effective camouflage confers two major benefits for the species: the first is that the female doesn't have to displace herself or to construct webs in order to capture prey. She simply sits on the flower and waits for pollinators to visit, and then eats them. This tough spider can and will take down even a wasp.

The second major advantage of the camouflage is that she doesn't have to do much to avoid predation. Predators will usually not even notice her (as you likely didn't notice her in that second photo, up above).

These two facts allow the female to devote a great deal of energy toward growing and producing her eggs, increasing her reproductive success.

This female also exhibited another very interesting behaviour. What happens if the spider isn't on a yellow or white flower? Well, I got to find out, as she got tired of my pursuit with my camera and jumped ship into the grass, treating me to this fascinating pose:

Misumena vatia imitating a flower
If I hadn't actually watched her assume this pose, I might well have glanced over this spider thinking she was an orchid or similar flower.

Animal adaptations to predation are quite fascinating, indeed!

Misumena vatia imitating a flower
My takeaway from this particular experience is: the next time somebody suggests you stop to smell the flowers, check that you're not sticking your nose into a spider's hunting ground first!

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