Surprise in a sweep net: my first thread-legged bug!


Portrait of a thread-legged bug (subfamily Emesinae) collected from a Joe-Pye weed (Eutrochium fistulosum) in my backyard. Photographed with a Zuiko 60 mm micro 4/3 macro lens & 25mm extension tubes. Magification = approx 1.5x.

 Yesterday I grabbed my sweep net and went out into the garden to mess around and see what I could collect. A sweep net is similar to a butterfly net but more strongly built so that it can be used to sweep back and forth through vegetation. I made mine out of an old pillow case, three wire coat hangers, the handle from a paint roller and plenty of duct tape. It isn’t pretty (something of an understatement) but it gets the job done.

But getting back to my story…I wandered around the garden and (gently) swept it through a few bushy plants. I was just curious to see what I would find. I didn’t think I’d find anything that was particularly interesting, but I was wrong! After a couple of sweeps I looked in the net and saw what I first thought (with my lousy vision) was a mosquito or midge because of the size and the long spindly legs. But when I looked closer I realized that it was something I had never seen before.

What I had caught (I subsequently discovered) was an appropriately named thread-legged bug, a type of assassin bug (family Reduviidae). But this was unlike any assassin bug I had ever seen before. As it turns out, the thread-legged bugs comprise a subfamily (the Emesinae) which is distinctly different from other assassin bugs because of their thin body and very long thin legs. They are a predatory insect and, as you can see in the photos, they walk on four legs with the front pair free and ready to grab their prey—similar to the stance of a praying mantis. You can also see the long pointed rostrum folded under the head. They impale their prey with their rostrum and inject saliva and digestive enzymes; then they suck up the resulting soup. This specimen was only 7mm (1/4 inch) long (not counting the legs).

Photo of a thread-legged bug (subfamily Emesinae) showing the distinctive thin body, long spindly legs, and grasping front legs which are not used for walking. Photographed with a Zuiko 60 mm micro 4/3 macro lens. Magification = 1x.

According to Wygodzinsky (1966) the wide spread of their long thin mid and hind legs is a preadaptation to life on spider webs! Apparently many species are often found on webs where they feed on either other insects that become trapped, or the spiders themselves. Wygodzinsky (1966) also noted that of the 86 valid emesine genera known at the time, about 20 were known only from a single species collected only on a single occasion! I wonder what those stats are like today?

I was definitely familiar with assassin bugs, but not thread-legged bugs. Discovering such a cool little insect in my own backyard—from a subfamily that was unknown to me—was just too cool! What made the event even better was the way the little critter posed for me. I just set it down on a leaf and took these photos. It hardly moved. It is really rare to have such a cooperative subject!

Another view of a thread-legged bug (subfamily Emesinae). This was the first shot I took. The leaf vein in the forefront is distracting, but it shows the insect nicely. Photographed with a Zuiko 60 mm micro 4/3 macro lens. Magification = 1x.

After shooting its portrait, I thought I’d try to entice it to feed for some more photos. I offered it a little fly (also collected in the sweep net) but it wasn’t interested. The fly might have been a bit big, so I ran inside and grabbed some drosophila (fruit flies) I have been culturing. But when I returned, the insect was gone. Funny how it sat perfectly still while I photographed it, then took off in the less than a minute I was away. Oh well, where there was one, (hopefully) there will be more.

I wonder what other surprises are lurking in my backyard?


Wygodzinsky, P. (1966). A Monograph of the Emesinae (Reduviidae, Hemiptera). Bull. Am. Mus. Nat. Hist. Vol. 133. New York. 614 pp.

The technical stuff:
Camera: Olympus OM-D E-M5
Lens: Zuiko 60mm micro four thirds macro
Settings: manual exposure (F11 @ 1/200 sec)
Lighting: Olympus RF-11 ring flash (TTL mode)
ISO: 200