Friday, June 17, 2005

ENV: Not-Really-a-Cat-Friday

Well, there's been some great critters around this week, but i have one i've wanted to write about, and am just getting the opportunity to because it's just now emerging from winter hiatus.

I happened to look out the office window last night (actually early a.m. Tuesday, June 14th) and saw a large flying bug circling underneath one of our mercury-vapor lights. Deducing it might be a Dobsonfly, i grabbed a camera i headed down there. Indeed it was, though it was so high up i couldn't tell if it was a male or female.

It appeared to be buzzing the pole, so a closer look revealed a female clinging to the pole. The first bug sailed up into the canopy and disappeared into the leaves, without my being able to ID it as male or female.

First of all, the kids bring me these things all summer (or rather, come and get me to look at this thing -- i can usually tell by the look on their face what they've found). However, i've never seen more than one at a time. So to have seen two together was pretty special. Then i noticed a third, a little lower down and, after some searching, i found a fourth on a nearby pecan tree. Looks at other lightpoles didn't turn up anymore, but when i returned there was a fifth on the original pole, and low enough down to get some good pictures (see below).

Like most large dragonfly-looking insects with lacey, celled wings, Dobsonflies spend the greater part of their lives underwater. Females lay masses of eggs on a rock or log near water, and when the larva hatch they crawl to the nearest water.

Kids always ask me similar questions about aquatic insects and turtles. When they hatch how do they know how to find water? Well, just speculation on my part (and research on the endemic turtles of the Guadalupe River has provided me no answers yet), i think they just move downhill. Water, pulled by gravity, does exactly that. The simple solution is that to continue moving downhill will eventually get you to water.

After reaching water, the larva feed voraciously on anything they come into contact with -- mayfly, stonefly, damselfly and dragonfly nymphs, copepods, water beetles, etc. This stage, which can grow to nearly two inches in length, live for two to three years underwater, and bite like, well Hell, are called Hellgrammites.

On leaving the water they crawl into damp soil near the stream and pupate for the winter. On some cue (that i'll have to see if i can find something about), they emerge as adults. The cue has to be important since the adults do not feed, and die within about 48 hours. Timing of emergence is critical.

The males have elongate pincers, about half the length of their bodies. That's the reason for the look in our kids' eyes. They look ferocious. But the pincers are used for grasping the females during mating, and are weak enough as to be harmless. The females however retain the stout mouthparts of the larvae and can wreak a little bit of havoc with skin.

If i find a male i'll add some pictures to the post later, although a second look tonight at the lights revealed none at all.

This particular Dobsonfly is a member of the genus Corydalus. I think it is an Eastern Dobsonfly, Corydalus cornutus, based on reading various descriptions and comparisons to photos of identified bugs. The Western Dobsonfly, Corydalus cognatus, also occurs in Texas, but is smaller with less dramatic pincers on the male.

Be sure to check out the weekly version of The Friday Ark at The Modulator.

Update: Although i posted this for the Friday Ark -- the critters were first found early a.m. Tuesday and written about shortly after. A check early a.m. Wednesday and Thursday revealed no more. But then early Friday a.m., i found and photographed two more females. Still no males as of this writing.

Update again: I was at a program at the waterfront last night (Sunday the 19th) and two female Dobsonflies were flying around the lights, one briefly landing on my chest. I checked again early a.m. the 2oth and found three females clinging to the pole. This is getting to be quite a fancy little concentration.

Update again: None present on the mornings of the 22nd or 23rd.



Eastern Dobsonfly, Corydalus cornutus
Females two through five, in order of discovery

Details of female number five
[i strongly recommend clicking on this last picture above
to see the high-res version -- get a load of those eyes!]



Females six and seven from June 17, 2005, early a.m.


Females eight, nine and ten from June 20, 2005, early a.m.


I also watched this cool longhorn beetle fly into the pecan or i never would have seen it. It was distant so the enlargement is fuzzy -- sorry.





And there was this fine moth on a limestone wall.



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