29 May 2009

Success! = Cordulegaster obliqua

Friday, May 29 started out with some great weather (sunny and calm) so I headed to Lower Huron Metropark at 1000 to obtain physical evidence of the spiketails.

Initially, I walked the forest edge in hopes of finding an adult Arrowhead Spiketail (Cordulegaster obliqua) to photograph. Unfortunately, I only saw one and it did a quick flyby at head height on the opposite side of the clearing and it didn't return.

Thus, it was time to check the rivulet. Ethan Bright hinted that I should dip for nymphs in the silty areas below the sticks and branches laying over the water of the streamlet. On about the sixth dip, I came up with a large nymph of a Cordulegaster.

This is the home of this nymph.

After identifying the specific structure of the nymph habitat, I began looking for exuvia. At 1130 and a bit upstream I "hit the jackpot" by finding an emerging female. Note the large ovipositor.

She was on a tree a few feet from the rivulet and is on the trunk at the left in the photo below.

Ethan Bright also noted that there may be different sizes of nymphs if these Cordulegasters require more than one year to mature. A bit further upstream I dipped a few more times and found another nymph which was a bit smaller than the first.

It was similar in habitat structure to the first, a hole below a log with a silty layer.

Given the couple of adults I observed over a few days and the nymphs being found relatively easily, it seems there is a decent population along this waterway. Nannothemis and I will return in a couple weeks to try and obtain good quality photos of the adults since there should be more flying.

I returned on 31-May-09 and found one male perched in a calm, sunny area at 1115. I was able to obtain only one photo, shooting through my binoculars.


John B. said...

Congratulations on the discovery!

Darrin OBrien said...

Thanks, john. Now the goal will be to get a good quality photo of an adult and to have Nannothemis see one. ;^)