crabspider

Rosier ou Eglantier

Rosier ou Eglantier, - Araignées-Crabes et Mouche à damier (damier= chequer board, from the black and white pattern on the abdomen of the fly.)

The roses which adorn our waysides confuse me because of the number of species, varieties and hybrids. In one common species (-the field rose or Rosa arvensis) the styles - the pollen receptors- cohere into an obvious column, Most have scentless flowers but quite a few have scented leaves. In the group of species called the Sweet Briars, they exude the scent of apple. As I approached the rose bush of the photo on a day with a temperature of 30 degrees, I sensed the smell from several feet away. The odour is released from many tiny pinhead glands. These can be seen glistening on the leaf edges.

But as I approached the plant I perceived one of those small dramas of nature which are commonplace but generally pass unnoticed. A crab spider was eating a flesh fly on a flower. Crab spiders are so called because they have large sideways projecting legs and look something like a crab, and moreover tend to walk sideways. They have the habit of sitting on flowers, or hiding just below the petals in order to pounce on some unwary visitor to the flower. This crab spider ( Misumena vatia), has also the knack of changing colour slightly between green white and bluish to match the flower which it chooses for the ambush. In this instance she (the males are only a third of the size) has caught a fly (the flesh fly or mouche à damier), behind the head, injected a paralysing toxin and is sucking out the juices. After a small while as I watched, the corpse was allowed to fall and the spider resumed its ambush.

The flesh fly in turn had spent its young larval life in the corpse of some dead animal, maybe one of the dead mice which I trap only too often in the house and throw at a distance away from the property! In this activity again there is an intriguing anecdote. The adult flesh fly does not lay eggs, but the larvae are in effect born in the active state. The fly drops these on the corpse, the flesh of which is dissolved by the larvae. The flesh fly has a keen sense of smell to detect fresh corpses and I guess had a keen sense to detect that of the rose flower to come to the nectar for its last meal. I did not detect a smell from the flowers, but only from the leaves.

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