Monday, July 15, 2013

June Beetle Grub


Barb spotted a big fat grub in our lawn at home and laid it on the patio table and said, "You have got to see this!"  As I watched, it twisted around from its C-shaped posture, rolled on its back and started crawling with its legs in the air.  I spent the next few minutes turning it over to get it to repeat the performance, a feat that it never tired of.  Check out it doing a backstroke on this video.

With the help of Google, I discovered that only the green June beetle, Cotinis nitida, and the bumble flower beetles, Euphoria, travel this way, and the June beetles are far more common.  Their legs are short and considered inadequate for travel but they wiggle them in the air as they go, as though that would help.  They have short stiff hairs on ridges of their backs which help them gain traction on the grass.

The third and final instar overwinters eight inches below the surface.  In the spring it burrows up closer to the surface, then moves through the soil on its back, feasting on decaying matter before forming a pupa.  It uses sticky secretions to hold soil particles together, forming a protective case from which the adult beetle will emerge in 16-18 days.

Green June Beetle- Wikimedia
The adults meet on your lawn, mate, then the female lays her eggs three inches deep in rich organic soil.  They might have to hunt for a home in nature, but they thrive where humans provide nurseries such as fertile lawns and gardens.  The eggs are buried in clusters of 10-30, wrapped up in a clump of dirt.

The grubs that emerge feed on decaying matter.  They are considered a serious pest on tobacco plants as they crawl through the soil, loosening and uprooting the plants.  They should be the symbol of the American Cancer Society campaign against smoking, but instead they are considered pests because of the damage they can do to lawns.

The large blue-winged wasp, Scolia dubia, is commonly seen flying low over grub infested lawns.  The female wasp actually digs into the soil to find green June beetle and Japanese beetle larvae.  She then stings a larva into paralysis and lays her eggs.  When they hatch, her larvae will consume the grub.  Even Japanese beetles have some benefit. 

To identify white grubs, go to this guide.

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