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Slacker Wrap-Up Part II: Wind-powered Leaping Larvae

August 23, 2011

ResearchBlogging.org
In a roly-poly world filled with roly-poly things (like tumbleweeds and peas), the ability to transform one’s non-roly-poly self into a blur of roly-poly-ness can be essential to survival.

Huh?

See Exhibit A: The pebble toad (Oreophrynella niger), a tiny toad that lives on the tops of mesas in Venezuela. When threatened by a tarantula, a pebble toad will curl itself into a ball and throw itself off a cliff.

 

Our second example comes from an awesome study [Wind-Powered Wheel Locomotion, Initiated by Leaping Somersaults, in Larvae of the Southeastern Beach Tiger Beetle (Cicindela dorsalis media)] that sets out to answer the question that drives the impish behavior of most 10-year olds: What happens if we poke it?

The larvae of the coastal tiger beetle (Cicindela dorsalis media) live in the sand at Cumberland Island National Seashore. When threatened (usually by the wasp Methocha, but in this study, by humans), the larvae propel themselves off the sand and flip through the air. Such roly-poly behavior is especially impressive because, as the authors point out, “leaping represents serious challenges to soft-bodied, elongate, short-legged or legless animals” like tiger beetle larvae.

Here are the details:

“Without benefit of high-speed video, however, a typical wheeling event looks like a brief and violent bout of thrashing on the sand, interspersed with an occasional leap, after which the larva suddenly and rapidly zips along the surface of the sand in a more or less straight line.”

Translation: To the naked eye, a threatened C. dorsalis media larva is a spaz. But with high-speed video we can see…

“When a larva is touched on the head, thorax, or anterior abdomen, it typically jerks or crawls away, threatens with open jaws without arching backwards, contracts its body into a sinuate death-feigning pose, or regurgitates.”

Translation: When you poke the larvae on the head or chest, it pukes, plays dead, bares its teeth or just walks away.

“When a larva is touched on the posterior part of the abdomen (i.e., from the fifth abdominal segment to the tail), it vigorously arches its body backwards so that its head snaps upwards and backwards and its tail (if not pinned to the substrate) arches upwards and forwards… The momentum of the head end coiling backwards causes the entire animal to roll backwards until the tail of the now-coiled animal contacts the substrate. As soon as its tail contacts the sand, the larva attempts to launch itself off the sand by arching its body suddenly in the opposite direction, using its tail as an anchor. The larva now forms a dorsal-side-out loop that rotates forward while in the air, often completing one to several rotations while airborne. When a larva lands on the sand, it typically will either fall over on its side or else start to roll. In the latter case it will either continue to wheel or else relaunch once its tail (or less commonly head) contacts the sand”

Translation: When you poke the larva’s butt (or anywhere near it), it flips, using its tail as a launch pad. When it lands, it stays in its roly-poly position and either rolls along the sand until it topples over or launches itself into another round of flying somersaults.

“This translates to a typical speed of 0.30–0.56 m/s), assuming a larva travels one body length per rotation. Under the high winds of 2007 (>12.5 m/s), we observed larvae that were wheeling faster than our assistant could run on the beach, which we calculated separately to be around 3 m/s.”

Translation: These guys aren’t all that fast under normal conditions, but in winds of almost 28mph they can wheel at a sub-9-minute mile pace.

Harvey, A., & Zukoff, S. (2011). Wind-Powered Wheel Locomotion, Initiated by Leaping Somersaults, in Larvae of the Southeastern Beach Tiger Beetle (Cicindela dorsalis media) PLoS ONE, 6 (3) DOI: 10.1371/journal.pone.0017746

 

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