Predator or Prey

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). 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.

The Assassin (Bug)

A colorful assassin bug (Reduviidae, Lick Creek Park).

Here’s a pretty little bug I’ve run into a number of places.  This is an assassin bug, a member of the family Reduviidae (which also includes the ambush bugs).  This diverse family of bugs take their name from their predatory habits.  They use their short sharp sucking mouthparts to stab their prey and inject lethal digestive chemicals which liquefies the prey’s internal structures.  In fact, although they are not particularly aggressive, many species can deliver a painful bite to humans if molested. One family, the aptly named kissing bugs, even makes a habit of biting humans in soft fleshy bits such as the lips to sip their blood.

A ventral view of the bee killer assassin bug (Reduviidae, Welder Wildlife Refuge).

This particular species of assassin bug, Apiomerus spissipes, is also called the bee assassin or bee killer, for its tendency to prey on bees and other pollinators as they visit flowers.  It is fairly widespread across the southern United States and among the more colorful and strikingly patterned of the assassin bugs.

Ambushed Wasp – The Ambush Bug

An ambush bug preys on an unwary wasp.

Exploring an Argentinean roadside I spotted what I thought was a dead wasp on a flower.   Wondering how this wasp had come to perish so abruptly in her nectar gathering work, I looked closer.  I actually poked at her several times before I noticed the second occupant of the flower—an ambush bug enjoying a tasty wasp meal!

Ambush bugs are a subfamily of Assassin bugs, family Reduviidae.  Ambush bugs are “sit-and-wait” predators.  These highly cryptic (camouflaged) insects frequently lurk around flowers, where they pick off unwary visitors.  They have mantis-like raptorial forelegs to snatch their prey from a safe distance.   Like other true bugs (order Hemiptera, suborder Heteroptera) ambush bugs have a segmented tube-like ‘beak’ for feeding.  Ambush bugs insert this beak into a weak spot in their prey’s hard exoskeleton and suck out the fluids.