Tuesday, October 5, 2010

Black and Yellow Beetles on Goldenrod

While day time temperature has been in the 60s and 70s, overnight the temperature has dropped into the 30s.  Only a few wildflowers are in bloom along the Chippewa River State Trail - the asters, boneset and goldenrods.

I can't resist checking the goldenrods for soldier beetles.  I haven't found any lately.  But I have spotted a number of black and yellow insects with red legs and a big yellow "w" on their backs.  At first I thought they were hornets.

What are they (and what are they doing)?

Locust Borer Megacyllene robiniae

They are Locust Borers, named for their association with Black Locust trees.  In September and October the adults feed on goldenrod pollen.  Look for them in the morning.  In late afternoon you can spot them on the trunks of Black Locusts, looking for crevices in the bark on which they lay their eggs.

When the eggs hatch, the larvae chew their way into the inner bark and spend the winter in "hibernation cells."  In the spring, they bore deeper into the wood and feed.  They pupate inside the tree in July and August, and emerge as adults in the fall. 

The Black Locust, an invasive legume, is not native to Wisconsin.  It was originally planted here to control erosion, and for use as fence posts.  You can see it along the Chippewa River State Trail and Rustic Road 107.  I can't help but notice it's fragrant white flowers in the spring.

It's similar to the Hickory Borer, which is active as an adult in the spring.

1 comment:

  1. This is a very interesting looking beetle. If anyone has the opportunity to spot one in the fall, take a close look at the front legs at what I would call the feet as they are very unusual and it would be interesting to find out why they have evolved in such a wonderful design.