Predator or Prey

27 Sep
A leaf-footed bug nymph (Coreidae).

A leaf-footed bug nymph in profile (Coreidae).

Look at the picture above and the one below.  You may notice a resemblance to some of the insects I’ve talked about in my most recent posts.  However, despite their similar appearance these bugs are actually two different types of insects from two very different families.  The insect above is an herbivorous leaf-footed bug (Coreidae), while the bug below is a carnivorous assassin bug (Reduviidae).  In fact, many leaf-footed bugs and assassin bugs in the field bear a striking resemblance to each other.

Assassin bug peering over a leaf (Reduviidae).

Assassin bug peering over a leaf (Reduviidae). The stridulatory groove can be observed on the prosternum.

How to tell them apart?  Those same sucking mouthparts that classify them both as hemipterans.   These beaks, or rostrums, may both be designed for sucking fluids but they also tell us something about the kind of food each bug eats.  Leaf-footed bugs, and other coreids are exclusively plant eaters.  Assassin bugs and other reduviids are exclusively predators.  As a rule of thumb, the beaks of herbivorous insects are longer than those of carnivores.  This is because most herbivorous insects need to pierce deep down into the tissue of plants to reach the sticky sap.  Predatory insects, on the other hand, have short stabbing knives of beaks to quickly pierce their prey and inject toxic digestive chemicals.

As you can see, the leaf-footed bug in the first picture has a beak reach most of the way down it’s body.  The beak of the assassin bug in the second picture is much shorter.  In fact, among reduviids this beak is the most diagnostic trait for identification.  The beaks of reduviids tuck under their heads and fit into a small notch in their sternum, or chest, called a stridulatory groove.  Reduviids can rub their beaks across the rough surface inside this groove to  create a rasping noise (stridulation) to warn off predators.

2 Responses to “Predator or Prey”

  1. Aty December 17, 2011 at 3:42 pm #

    Thanks for the info. I have wondered how to tell the difference between the two. Do reduviids also produce the typicaly stinkbug scent like coreids? Also, can I assume that if the hind legs are big that it is probably a coreidae and not a reduvid?

    • 6legs2many December 18, 2011 at 4:54 pm #

      I didn’t know the answer to this off the top of my head since I generally try to avoid overly distressing the reduviids to avoid a bite. But they do, indeed, have a metathoracic scent gland just like coreids. I seem to remember the wheel bugs I pinned smelling a bit similar to the big leaf-footed bugs. Scent glands are apparently extremely common in the nymphs of most true bugs, with metathoracic scent glands in the adults of some true bug families.
      While I can’t think of any reduviids with enlarged hind legs off the top of my head, there’s a lot of variation, especially in coreids (who may have regular hind legs). A more helpful rule of thumb is that reduviids tend to have abdomens where the sides rise up slightly encompassing the wings while coreids are generally flat-backed. This isn’t 100%, but I find it’s a pretty good rule of thumb for quick field IDs.
      Here’s a good example:

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