Running Crab Spider on Window

2023 April 2

This lovely little spider was on our dining-room window on March 11, 2023. I am pretty sure it is the same species that we regularly see in the winter and early spring, like this one that we found on in our mailbox on a christmas card back in 2015. They vary a bit in color, but they all have that nearly circular cephalothorax with a white band down the middle and dark on the sides, and eyes that are visible from above.

I’ve decided that they are most likely Running Crab Spiders in the genus Philodromus, mostly based on the lengths of the legs, the shape of the cephalothorax, and the size and arrangement of the eyes. I can’t narrow it down much more than that, though. The ones I can find on BugGuide that actually look like these are not identified to species, because they are juveniles and so haven’t developed their mature features. So, I think these are probably the juvenile overwintering form, and may look rather different once they grow up.

I did get one shot that shows something I don’t normally see in pictures of spiders. The light was just right to catch the silk “dragline” that spiders lay down behind them as they walk.

Usually, the dragline is so thin and transparent as to be invisible to the naked eye, but at the correct angle the sun can illuminate it so you can see it. Spiders lay this down as they walk, so that if they either lose their grip and fall, or jump off to evade a predator, they can climb back up to where they started. I expect this is particularly useful for web-spinning spiders, as it allows them to get back to their webs easily. But even non-web-spinning spiders evidently find the dragline helpful. They don’t quite use it the way spider-man does (since he shoots webs towards his destination and then swings along it), but they can drop slowly down from high places and recover from stumbles, so it is probably the next best thing to flying.

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