Thursday, April 15, 2010

Green Dock Beetle

 These bright bluish-green metallic beetles are called Green Dock Beetles (Gastrophysa cyanea). They are leaf beetles in the family Chrysomelidae, and feed on plants in the Dock family. I was near our pond dam when I noticed a large cluster of weeds with numerous holes eaten in the leaves. To a bug hunter this means one thing; some 6-legged creature is hungrily munching down on said leaves. This called for an investigation. I discovered dozens of these tiny beetles all over the leaves, most were engaged in mating behavior, and those who weren't were busy eating leaves. What a and eating...eating and sex....! I had no clue what kind of weeds they were, nor did I have a clue what these beetles were. After sending my pictures to bugguide I had an answer in 5 minutes. The beetle is the Green Dock Beetle and the plant is a form of Dock, called Curly Dock.

  This is a picture of the actual Curly Dock (Rumex crispus) plant. If you look closely you can see many of these very tiny beetles on the leaves. Curly Dock is a perennial closely related to buckwheat. It can grow up to five feet tall. This weed prefers moist environments, such as near our pond. It is commonly found near wetlands, hayfields, pastures and some agricultural crops. Curly dock does not survive well during drought years, which explains why we have it such large quantities, this past year as been extremely wet.

 Males (left) are smaller than the females. Barely measuring a 1/4 of an inch. The female is larger, at just over a 1/4 inch. Once mated she far outshine him in the girth department though. Her abdomen is hugely disproportionate to the size of the rest of her body. Which apparently engorges with eggs. Her wings aren't even able to cover her enlarged abdomen. After mating, the female will lay yellow eggs on the underside of the leaves on the plants they feed on.

(Female, notice the engorged abdomen?)
  The munching habits of the adults, and later the larvae is enough to keep the Curly Dock in check, and to control the continued spreading of what many people consider a noxious weed.
 (The larvae, newly hatched and very tiny, approximately 1/10 of an inch)

I am amazed that as long as I've lived here (20 years) this is the first I've ever spotted these beetles. Each year it seems I find something new crawling around on 6 legs.


  1. very cool... we have curly dock here, but never noticed anyone grazing on them... will have to have a good look next time i'm around the dock :D

  2. I've had curly dock here for years, this is the first year I noticed anything feeding on it. They are interesting little beetles, especially the females with their over-sized abdomens.

  3. Some years they seem to be really abundant - like this year. I wonder if wet springs are part of the reason.

  4. This is the first year I've ever noticed them, perhaps it is just the right weather conditions that cause such large numbers, and heaven knows this has been a really wet year.

  5. im only 13 and i knew almost all of this stuff and i love collecting them and putting them in a tub the most i ever got was 294 in 1 tub but i always let them all go

  6. I'm glad you stopped by for a visit, I am so excited to hear that you like insects. I've never seen these beetles before this year, and I was fascinated by them. They really are a pretty little beetle.

  7. Rock around the dock clock! Very cool post - it is good you found more than one life stage. Chrsyomelids are such important beetles that get so little respect.