Sluggin' Along: Spider Stalker

The thread-legged bug Stenolemus lanipes lives an interesting life. In spite of its seemingly flimsy build, it preys on spiders. You'll usually spot one of these assassins (Reduviidae) creeping dangerously close to a spider's web. With its raptorial forelegs and agonizingly slow movements, S. lanipes resembles a mantid. In fact, I mistook the species at first for a kind of mantid. It hunts by one of three ways:

1. Stalking and ambushing the spider
2. Mimicking prey (e.g. plucking the web) to draw the spider into a trap
3. If all else fails, stealing the spider's prey

I found my specimens (an adult and a couple of juveniles) on the siding of our house, stalking the cribellate orb weavers (Uloborus glomosus) that have built their webs in the corner between the hot water heater and the wall. The cribellates look much more robust than the thread-legged bugs, but don't be deceived: the assassins are quite skilled. And they're so thin and wispy, so delicate, you can easily overlook them. Not to mention their mantid-like gait. I've noticed a juvenile climbing into one of the cribellate's webs. Brave little creatures. And yet the spiders probably dismiss them as something not worth eating. Little do they know...

Interestingly, S. lanipes will NOT feed on insects (specifically Drosophila, or fruit flies) placed in the web. They'd rather starve first. Evidently, if the spider didn't catch it, S. lanipes won't eat it. You can read about such behavioral characteristics in this article:
http://www.americanarachnology.org/JoA_free/JoA_v12_n3/arac_12_3_0369.pdf

Juvenile: