Tag Archives: insects

How do insects walk on water?

A new study illuminates this shadowy question. First, the video:

And now, a press note from the American Chemical Society:

Water striders’ ability to walk and jump on the surfaces of ponds and lakes has long amazed curious observers — and inspired robot designers who want to mimic the bugs’ talent. Now, scientists have measured for the first time key parameters that allow them to walk on water — by studying their leg shadows. The findings, reported in the ACS journal Langmuir, could contribute to designs for water-skimming robots.

More than 2,000 years ago, Greek scientist Archimedes explained flotation, stating that the upward, floating force on an object in water equals the weight (or downward force) of the water displaced. The principle has informed the building of ships, submarines and other aquatic vehicles. But for tiny water striders, water isn’t displaced. It is expelled by the insect’s hairy legs. The updated Archimedes principle predicts that the weight of the expelled water should equal the floating force. But confirming this prediction experimentally is a challenge. Because water striders are so light, they are almost impossible to weigh using conventional techniques. So Yu Tian and colleagues used an unconventional method — analyzing the shadows cast by the insects’ legs.

The researchers placed a white sheet of paper at the bottom of a lab aquarium housing water striders and installed a light source above the water. The insects’ stick-straight legs cast shadows that were rounded, representing the curvature of the water and the expelled water volume from which the floating force and weight can be calculated, the researchers say. Also, from these measurements, the striders’ slightest shifts in weight and body angle could be detected for the first time.

The authors acknowledge funding from the National Natural Science Foundation of China.

The abstract from the original publication:

Forces acted on legs of water-walking arthropods with weights in dynes are of great interest for entomologist, physicists, and engineers. While their floating mechanism has been recognized, the in vivo leg forces stationary have not yet been simultaneously achieved. In this study, their elegant bright-edged leg shadows are used to make the tiny forces visible and measurable based on the updated Archimedes’ principle. The force was approximately proportional to the shadow area with a resolution from nanonewton to piconewton/pixel. The sum of leg forces agreed well with the body weight measured with an accurate electronic balance, which verified updated Archimedes’ principle at the arthropod level. The slight changes of vertical body weight focus position and the body pitch angle have also been revealed for the first time. The visualization of tiny force by shadow is cost-effective and very sensitive and could be used in many other applications.

Citation: Yelong Zheng, Hongyu Lu, Wei Yin, Dashuai Tao, Lichun Shi, and Yu Tian. 2016. Elegant Shadow Making Tiny Force Visible for Water-Walking Arthropods and Updated Archimedes’ Principle. Langmuir 2016 32 (41), 10522-10528. DOI: 10.1021/acs.langmuir.6b02922

Treecology: A Children’s Nature Book Worth A Close Look

Treecology: 30 Activities and Observations for Exploring the World of Trees and Forests is an excellent new nature activity book for kids of a fairly wide range of ages.

Like a tree, the pattern of the book is pretty straightforward but fractal like; you start off simple but end up pretty much anywhere in the world of ecology. The book begins with the basic definition of a tree, simple tree anatomy, some phylogeny, some tree physiology and biology, but then branches off (pun intended) into things that are related to trees, like things that live on them, eat parts of them, etc. Seeds and seed dispersal come in around this point as well, as one might expect. The role of trees, or tree related images or tree names, etc. in human culture is also explored.

As indicated by the subtitle, these lessons are organized into thirty things you can do. Some of these things simply involve looking (dividing your local landscape’s larger plants into “tree” and “not a tree,”, etc.) while some involve more intense observation (like telling different trees apart) or interaction (including, of course, waxing leaves and similar activities).

The book includes some great tips on observing (or attracting) forest insects. I think Huxley’s Buggy Camp could have used some of this info this week to help them find tree-related buggy creatures in the nearby woods.

This book can probably work in any North American region, as it is not too specific at the species level, and pretty generic at the genus level. As it were. There is more than enough activity in this book, in terms of both amount and diversity, to keep a family with any number of kids busy on several weekends. The activities are also spread out across seasons fairly well.

Monica Russo has written and illustrated several nature books for children, and authored “Nature Notes,” a column in the Sun Chronicle. Kevin Byron is a nature photographer who’s work is widely recognized.

The book, published by Chicago Review Press, will be out on September 1st, but I think you can actually order it now.

No place to sit down (or, why do the Efe let some insects live?)

I knew a couple who had spent a lot of time in the Congo in the 1950s. He was doing primatology, and she was the wife of the primatologist. And when she spoke of the Congo or Uganda, where they spent most of the time, she always said “The thing about Africa is that there’s no place to sit down.” Continue reading No place to sit down (or, why do the Efe let some insects live?)