What's this bug? - Locust Borer

One of the common features of my job is that people are always asking me to identify things they have found in the wild.  If someone walks into the office carrying a jar, I can be assured that I am going to be asked to identify an insect.  I am not an professional entomologist (someone who studies insects), but I try to help if I can.  With that in mind, I am going to start a semi-regular feature of this blog on insect identification.

So... What's this bug?

Locust Borers exhibit a type of mimicry known as Batesian mimicry.  This means that they are harmless, but look like something dangerous (such as a wasp)

First of all, the animal pictured is a beetle not a "bug".  Both beetles and bugs are insects - animals with an exoskeleton, three body segments (head/thorax/abdomen), and six legs.  Bugs are a certain type of insect (shield shaped body, wings that cross over to form an x-shaped pattern while at rest, and a piercing mouth used for sucking juices), but the word "bug" is often used to mean any insect regardless of species.  Unlike bugs, beetles have a mouth designed for chewing.  Beetles have two pairs of wings, but the outer pair of wings have hardened into a protective covering for the soft inner pair.  This hard outer pair of wings is known as elytra (singular is elytron).

So we have established that this insect is a beetle, but which one?

Specifically, it is a Locust Borer (Megacyllene robiniae).

Locust Borer feeding on goldenrod pollen.

Locust Borers are named because their larvae bore (tunnel) into and through the wood of Black Locust (Robinia pseudoacacia) trees.  In small Black Locust trees this tunneling may actually kill the tree.  The adult can be found in the fall feeding on pollen, especially goldenrod pollen.

The tree and beetle are probably not native to Michigan.  The tree was introduced in the 1800s and often grown for use as fence posts due to its natural rot resistance.  The beetle was likely introduced at the same time.

With its yellow and black color scheme, the Locust Borer is easy to see.  This might seem like it would be a bad thing.  It's easy to see so birds and other predators should be able to pick it off.  Instead these colors act as a form of protection.  By mimicking the color pattern of bees and wasps, this harmless beetle is protected from animals that would be wary of a wasp's sting.  This type of mimicry is known as Batesian mimicry.