Title

The efficiency of black widow gumfoot lines

Poster Number

28

Format

Poster Presentation

Abstract/Artist Statement

Like other theridiid spiders, the black widow (Latrodectus hesperus) constructs gumfoot lines at the bottom of its cobweb. Gumfoot lines are vertical strands of silk that are tautly attached to the surface and detach easily when an insect touches them. Previously, I found that the median weight that the gumfoot lines could pick up was 10 mg. Here, I show that the gumfoot acts like a spring when it picks up a weight. The thread is already stretched when it is attached to the ground. When the gumfoot detaches, it uses the stored energy to pick up the weight. I wanted to find out how much energy went into and out of the system as the thread was stretched and unstretched. Using a force transducer, Tensiometer 400A (50.0 mN Force), I was able to stretch the gumfoot lines each 3 times at 2 and 10% of their original length. I could then calculate the efficiency and the strain. At 2% (pre-yield) it was found that the gumfoot had an efficiency of about 8 l .4%, but at 10% (post-yield) had an efficiency of about 23.9%. What this means is that not all the energy put into the stretch comes out again when the gumfoot relaxes. Knowing that the median weight that gumfoot lines can pick up is 10 mg and that they have a high efficiency, gumfoot lines are an ideal catching tool for black widows provided they are stretched less than 2% of the original length. (NSF DBI-0112165).

Location

Pacific Geosciences Center

Start Date

20-4-2002 9:00 AM

End Date

20-4-2002 5:00 PM

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Apr 20th, 9:00 AM Apr 20th, 5:00 PM

The efficiency of black widow gumfoot lines

Pacific Geosciences Center

Like other theridiid spiders, the black widow (Latrodectus hesperus) constructs gumfoot lines at the bottom of its cobweb. Gumfoot lines are vertical strands of silk that are tautly attached to the surface and detach easily when an insect touches them. Previously, I found that the median weight that the gumfoot lines could pick up was 10 mg. Here, I show that the gumfoot acts like a spring when it picks up a weight. The thread is already stretched when it is attached to the ground. When the gumfoot detaches, it uses the stored energy to pick up the weight. I wanted to find out how much energy went into and out of the system as the thread was stretched and unstretched. Using a force transducer, Tensiometer 400A (50.0 mN Force), I was able to stretch the gumfoot lines each 3 times at 2 and 10% of their original length. I could then calculate the efficiency and the strain. At 2% (pre-yield) it was found that the gumfoot had an efficiency of about 8 l .4%, but at 10% (post-yield) had an efficiency of about 23.9%. What this means is that not all the energy put into the stretch comes out again when the gumfoot relaxes. Knowing that the median weight that gumfoot lines can pick up is 10 mg and that they have a high efficiency, gumfoot lines are an ideal catching tool for black widows provided they are stretched less than 2% of the original length. (NSF DBI-0112165).