Predation scene (Runcinia grammica + Apis mellifera)

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During my naturalist walks, I was given several times the opportunity to witness this perfectly strange scene: a honeybee, motionless, on a flower. Perfectly strange, because she does not present the agitation, the eagerness that is usually lent to bees foraging for flowers. To the question “What does she do?” the viewer’s imagination could catch fire, but to find out what it really is, we have to change our perspective. This change often occurs when we shift our point of view, get closer to the bee, look under the flower… Then comes the truth, which transforms this bucolic scene into a macabre scene: the bee is motionless because it has been predated by a spider of the Thomisidae family.

Thomisidae form a vast family with 2153 species distributed in 169 genera. Spiders in this family can be identified notably by their legs I and II, which spread out on the side, giving the impression that they want to hug you (or give you the kiss of death if you are an insect). They do not weave webs to hunt; instead, they tend patient ambushes to their victims. Their first two pairs of legs are used to firmly hold their prey, while biting them. Many spiders hunt without weaving webs but by being active, in motion: the immobility which is used by Thomisidae is thus not common. Some Thomisidae hunt close to the ground and are therefore rather generalist in terms of prey, while others settle at flowers. As a particular fauna frequents this floral environment, these Thomisidae have become «specialists» of this particular fauna, namely some Hymenoptera (such as honey bees or bumblebees), Diptera (such as hoverflies), or Lepidoptera. They patiently wait for a prey to land on their flower, near them, and then they suddenly and quickly attack often at the head. Within seconds, the prey is neutralized. However, all attacks are far from being successful, which could explain why they are not strictly specialists and that they end up attacking everything that is within reach.

One of the best known Thomisidae is probably Misumena vatia, which has the amazing ability to change color (in a range however limited from white to yellow, and the process takes several days) depending on its hunting support, in order to fade into the background and go unnoticed. Moreover, we often see these Thomisidae which live on the flowers only when they move to shelter themselves from the shade of the naturalist approaching their flower, which can make life hard for anyone who wants to photograph them. Here, it is not this species, but another: Runcinia grammica. It sometimes looks like M. vatia, but the sharp eye will know how to differentiate them. One trick is to look at the eyeblock: R. grammica has a white keel that separates the anterior and posterior eyes. The keel of the individual which is predating the honeybee is not really visible here, the one of the male is however much more visible. You can notice the striking difference between male and female. This phenomenon, called sexual dimorphism, is relatively important in this species as well as in other Thomisidae which hunt on flowers.

 

 


Last update : February 11, 2021

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