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Why daddy long-legs are so cool

A daddy long leg. Image from arachnology.org

I started catching creepy crawlies before I could walk — or at least that’s what my parents insist I did. When I was two, I caught a spider in my preschool sandbox by cupping it with a baby food jar. I remember that spider just barely fit into the mouth of the jar because it was HUGE; or at least I certainly thought it was. With this in mind, it’s probably not hard to believe that there are few things that make me squirm… except daddy long legs.

To be totally clear, contrary to popular notion, daddy long legs are not spiders. They arise from an entirely different order and lack many of the segmentation and life history patterns observed in spiders.

Daddy long legs are characterized by having eight, long, spindly legs surrounding a bulbous body (although there are some short-legged forms). Their legs can sometimes be so thin that their much heavier body seems to float through the air as they gallump about their daily chores. When they have eyes, they only have one pair, which are placed sideways rather than facing forward. These eyes do not functionally project a usable image; so they have modified their second set of legs to effectively act as antennae to help them tap their way around as they either quietly ambush or actively chase down their prey. Unlike most other arachnids, which live off a liquid diet, daddy long legs consume their prey in chunks.

All these characteristics make daddy long legs rather sinister; yet, whenever my hair stood on end as a daddy long leg made an appearance in the room, I found myself inexplicably drawn to the same question over and over and over again: How do these animals support such a heavy body on such skinny legs?

Photo by Will Cook, http://www.carolinanature.com

I started looking in to this question several years ago and was stunned by what I found. Despite having such skinny legs, Schultz (2000) showed that the muscles are both numerous and complex. While the bulk of the muscle lies close to the hard, carapacial body, long tendons extend all the way to the tippy tips of the legs (often 50+ segments away!!), enabling fine, prehensile motion. This prehensile motion is used to help them climb thin structures such as grass blades, enabling them to wrap their leg completely around a single blade! More detailed studies by Guffey and colleagues (2000) on the microscopic morphology of these leg tips showed that there indeed is only a single tendon that extends to the toe tip, enabling prehensile motion. I couldn’t help but wonder how such a complex, prehensile motion across so many segments could be possible by means of a single tendon, and how this type of design could be applied industrially for highly mobile, exploratory devices… Thoughts? Does anyone know if something like this already exists in true mechanical models?

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  1. Jay
    6 September, 2010 at 15:48

    Yuck. I hated daddy long legs when I was little too. I remember going camping and they were ALWAYS on the inside of my tent climbing around the ceiling…and I remember pulling their legs off (OK, I wouldn’t do that anymore, but I was a kid.)

    One thing I know of (from recent experience) that uses similar technology are scopes in doctor’s offices. I just noticed these new things that are very thin “snakes” w/a light at the end, and the entire thing is segmented so it can bend and stay in position. After the doc numbs your nose…up goes the probe and it ends up in your throat! It tickles a little bit…just thought I’d share 🙂

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