Wednesday, March 16, 2011

Somebody Lost Her Head

A few weeks ago an odonatist friend made a general request of photographers to look through their photos and see how frequently adult dragonflies other than libellulids (skimmers) are hosts for water mites. When you spend a lot of time looking at odonates, it becomes clear that certain groups (like several libellulid genera and a variety of damselfly genera) are frequent water mite hosts, while other dragonflies in non-libellulid families and some libellulid genera rarely host water mites even if they breed in aquatic habitat that is suitable for mites. The subject of water mites is an interesting one and I’ll write more about them another time, but all of this leads me to the real subject of this post...

So, I was scanning through my dragonfly photo collection looking for water mite carriers, when I came across a male Diminutive Clubtail (Gomphus diminutus) that I photographed in South Carolina a few years ago. I noticed that it had a reddish-brown, bulbous thing on one of its front legs which looked superficially like a water mite except that it was too big and legs are a strange place for a water mite to make its temporary home (typically they attach to the lower areas of the thorax and abdomen). I decided that it wasn’t a mite, but I couldn’t really tell what it was.

A male Diminutive Clubtail (Gomphus diminutus) in Chesterfield County, South Carolina, 9 May 2008.
See the reddish-brown thing on one of the front legs under the head?






Digitally zooming in on the dragonfly’s front leg, the UFO (unidentified femoral object) began to take on a recognizable shape, but I wanted to be sure. I indicated that I collected this individual in the photo’s metadata and I’m glad I did that. Since I started odonate photography in a serious way, I’ve been cross-referencing photos to collected specimens and vice versa which can be really handy for a variety of reasons. One reason is that I have the specimen to verify the identity of the photographed odonate (important for more cryptic, difficult-to-identify species); another is that I can verify the body and eye colors of a specimen in life (eye color does not preserve at all in specimens and body color can fade or darken significantly).

I pulled the specimen out, put it under the microscope, and the UFO was what I thought it was—the head of an ant gripping the clubtail’s leg with its mandibles. Like many gomphids, the Diminutive Clubtail frequently perches on the ground and I presume that the ant came along and took on the dragonfly as potential prey, as misguided as that may be. The location on the front femur where the ant head held tight is within reach of the clubtail’s mandibles, so I’m sure that the dragonfly simply bit down on the ant’s body and yanked. The ant was resistant, of course.

A close-up of the photo above. Yeah, that’s an ant’s head.




Ants are a major threat to emerging odonates—they can’t fly or run and the exoskeleton is very soft and vulnerable to pinching mandibles. Emerging odonates don’t stand a chance when they are discovered by ants, but mature odonates simply fly off when their personal space is invaded. This ant must have grabbed on before the clubtail could take off, but it was a lethal mistake.

I find it easy to anthropomorphize odonates and I imagine this clubtail showing off the “trophy” on his upper arm as the victor of an epic battle. I’m sure the clubtail didn’t intentionally leave the ant’s head on his femur, but anthropomorphizing is fun sometimes.

6 comments:

  1. That is quite a war trophy on its leg. Great post.

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  2. Glad to see you posting again. Here's a blog that you might be able to help out with an ID: http://falltoclimb.wordpress.com/2011/03/25/forgotten-photo-friday-sympetrum-vicinum-autumn-meadowhawk-dragonfly/ She's in Canada, somewhere.

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  3. @Nature ID (Katie) Thanks, Katie. I just offered my two cents.

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  4. Ho, that"s quite a story--thanks for sharing!

    --Patricia Lichen, www.patriciaklichen.com

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  5. Jim, I just came across a blog post of a tiger beetle with an ant head attached near the mouth. Some discourse is going about why it happens. Are ants predator/defensive or prey? Thought you might be interested: http://beetlesinthebush.wordpress.com/2011/08/15/predator-or-prey/

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  6. @Katie (Nature ID) Thanks, Katie. I left my two cents there too, for what it's worth.

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