Spiders under the influence

Field picture of an urban web. Dark paper is used to make the web more visible for data collection

The activities are as follows:

People use pharmaceutical drugs, personal care products, and other chemicals on a daily basis. For example, we take medicine when we are sick to feel better, and use perfumes and cologne to make ourselves smell good. After we use these chemicals, where do they go? Often, they get washed down our drains and end up in local waterways. Even our trash can contain these harmful chemicals. For example, when coffee grounds are thrown into the trash, caffeine gets washed into our waterways.

Animals in waterways, like insects, live with these chemicals every day. Many insects are born and grow in the water, absorbing the drugs over their lifetime. As predators eat the insects, the chemicals are passed on, working their way through the food web. For example, spiders living along riverbanks feed off aquatic insects and absorb the drugs from their prey.

Just as chemicals change human behavior, they change spider behavior as well! Effects of drugs on spiders have been studied since the 1940s. Dr. Peter Witt first discovered that chemicals change spider web construction. Peter gave caffeine, and a few other drugs, to spiders to see if they would build their webs during the day instead of at night, which is when they usually work. After giving his test spiders some of the drugs, the spiders still created their webs at night. However, he noticed something unexpected – the web structure of spiders on drugs was completely different from normal webs. The webs were different sizes and had more spacing between each thread. Normal webs help spiders to easily catch prey. Irregularly shaped webs were not good at catching prey because insects could fly right through the large spaces. After his study, Peter knew that drugs were bad for spiders.

Chris (they/them), a current resident of Baltimore and a spider enthusiast, lives in a watershed that is affected by chemical pollution. They wanted to build on Peter’s research by looking at spider webs in the wild instead of in the lab. Chris knew that many types of spiders live near streams and are exposed to toxins through the prey they eat. Chris wanted to compare the effects of the chemicals on spiders in rural and urban environments. By comparing spider webs in these two habitats, they could see how changed the webs are and infer how many chemicals are in the waterways.

Chris worked with Aaron, a local high school teacher, to do this research. They collected images of spiderwebs in areas around Baltimore. They chose two sites: Baisman Run, a rural site far from the city, and Gwynns Run, an urban site close to the city. Chris traveled to the sites and took pictures of eight spiderwebs at each location. Chris and Aaron expected that urban streams would have higher concentrations of chemicals than rural areas because more people live in cities.

When they got back to the lab, Aaron took the pictures and used a computer program to count the number of cells and calculate the total area of each web. These data offer a glimpse into whether spiders near Baltimore are exposed to harmful pharmaceutical chemicals and personal care products. If spiders are exposed to these chemicals, the webs will have fewer, but larger cells than a normal web. The cells will also have irregular shapes.

Featured scientists: Chris Hawn from University of Maryland Baltimore County and Aaron Curry from Baltimore Ecosystem Study LTER

Flesch–Kincaid Reading Grade Level = 7.8

Additional teacher resources related to this Data Nugget include:

  • You can watch Aaron describe his Research Experience for Teachers project here.

Working to reduce the plastics problem

stretching the raw, preformed polymers
Nick (right) and one of his students (left) stretching the raw, preformed polymers.

The activities are as follows:

Plastics are materials that can be shaped easily and are used for many functions. This has made them extremely popular across the world. Thousands of products are made using plastic, including parts of cell phones, food wrappers from your lunch, and even the stitches you may need after an injury. In fact, if you look around right now, you can probably spot at least ten items made of plastic!

Once a plastic is made, it tends to stick around. Synthetic plastics, made by humans from petroleum, cannot be broken down by nature’s decomposers – bacteria and fungi. This means they impact the environment for many, many years. Some types can take thousands of years or longer to break down! 

Nick is a chemist concerned with the negative impacts caused by plastics. He knows that in order to reduce the amount of synthetic plastics in the environment, we need an alternative. And, this alternative needs to be just as good as the synthetic plastic it is replacing. Nick and his undergraduate students at Northland College are testing new ways to make plastics that are biodegradable, meaning they can be decomposed naturally and won’t last as long in the environment. His research focuses on stretchy plastics, called elastomers.Elastomers are what make up rubber bands, tires, hoses, non-latex gloves, and many more items we use every day. 

To try to solve the problem of making a biodegradable elastomer that has all the qualities of a synthetic one, Nick and his students got to work. First, they had to consider the chemical structure of plastics. Plastics are made of polymers. “Poly” means “many” and “mer” means “parts”. This means that plastics are made of long chain molecules with many repeating parts. These repeating parts are called monomers. Different monomers can be used to make different types of plastic.

Nick chose to test two biodegradable monomers – diglycerol and meso-erythritol. Diglycerol is cheap and easy to buy. However, it might be too soft when used on its own. Meso-erythritol is more expensive, but more rigid. They wanted to use diglycerol and meso-erythritol because the chemical structures have the potential to create something that is not too rigid and not too flexible.

Nick and his students designed an experiment in which they tested elastomers made from each of the monomers (diglycerol and meso-erythritol) alone, as well as elastomers made using both types of monomers. They made elastomers with the following percentage ratios of diglycerol over meso-erythritol: 100/0, 75/25, 50/50, 25/75, 0/100. The team was hoping to find the “sweet spot” between a product that is too stiff, and one that is not stiff enough to be useful in elastic materials. Once they finished making their elastomers, they prepared the stretch tests. 

To start a stretch test, the team had to stamp out a piece of material from each elastomer, creating samples with the same size, shape, and thickness. They also cut pieces from rubber bands made of synthetic plastics to compare as a control. Next, they tested the elastomers using a machine that measures how much force is applied (stress) as a material is stretched (strain), both important measures of elasticity. The stress, or force per unit of area, is measured in megapascals (MPa) while the strain, or amount of stretch, is measured as a percent of the original length. 

Featured scientist: Nick Robertson from Northland College. Written by: Theresa Paulsen from Ashland High School, Wisconsin

Flesch–Kincaid Reading Grade Level = 9.6

For additional information on the plastic problem, and Nick’s research, check out the following resources:

Alien life on Mars – caught in crystals?

Magnesium sulfate crystals trapping liquid water.

The activities are as follows:

Is there life on other planets besides Earth? This question is not just for science fiction. Scientists are actively exploring the possibility of life beyond Earth. The field of astrobiology seeks to understand how life in the universe began and evolved, and whether life exists elsewhere. Our own solar system contains a variety of planets and moons. In recent years scientists have also discovered thousands of planets around stars other than our Sun. So far, none of these places are exactly like Earth. Many planets have environments that would be very difficult for life as we know it to survive. However, there are life forms that exist in extreme environments that we can learn from. On Earth there are extremely hot or acidic environments like volcanic hot springs. Organisms also live in extremely cold places like Antarctic glacier ice. Environments with extremely high pressure, like hydrothermal vents on the ocean floor, also support life. If life can inhabit these extreme environments here on Earth, might extreme life forms exist elsewhere in the universe as well?

A view of the astrobiology lab.

Charles is an astrobiologist from Great Britain who is interested in finding life on other planets. The list of places that we might look for life grows longer every day. Charles thinks that a good place to start is right next door, on our neighboring planet, Mars. We know that Mars currently is cold, dry, and has a very thin atmosphere. Charles is curious to know whether there might still be places on Mars where life could exist, despite its extreme conditions.While there is no liquid water on the surface of Mars anymore, Mars once had a saltwater ocean covering much of its surface. The conditions on Mars used to be much more like Earth. Liquid water is essential for life as we know it. If there are places on Mars that still hold water, these could be great places to look for evidence of life. Charles thought that perhaps salt crystals, formed when these Martian oceans were evaporating, could trap pockets of liquid water.

Charles and his fellow researcher Nikki knew that there are a number of kinds of salts found in Martian soils, including chlorides, sulfates, perchlorates and others. They wanted to test their idea that water could get trapped when saltwater with these salts evaporate. They decided to compare the rate of evaporation for solutions with magnesium sulfate (MgSO4) with another commonsalt solution: sodium chloride, or table salt (NaCl). They chose to investigate these two salts because they are less toxic to life as we know it than many of the other chloride, perchlorate, or sulfate salts. Also, from reading the work of other scientists, Charles knows the Martian surface is particularly rich in magnesium sulfate.

Charles and Nikki measured precise quantities of saturated solutions of magnesium sulfate and sodium chloride and placed them into small containers. Plain water was used as a control. There were three replicate containers for each treatment – nine containers in total. They left the containers open to evaporate and recorded their mass daily. They kept collecting data until the mass stopped changing. At this point all of the liquid had evaporated or a salt crust had formed that was impermeable to evaporation. They then compared the final mass of the control containers to the other solutions. They also checked the resulting crusts for the presence or absence of permanent water-containing pockets. Charles and Nikki used these data to determine if either saltmakes crystals that can trap water in pockets when it evaporates.

Featured scientists: Charles Cockell, UK Centre for Astrobiology, University of Edinburgh, & Nikki Chambers, Astrobiology Teacher, West High School, Torrance, CA

Flesch–Kincaid Reading Grade Level = 8.7

Additional teacher resource related to this Data Nugget:

Sticky situations: big and small animals with sticky feet

Travis in the lab measuring the stickiness of a gecko’s toe.

Travis in the lab measuring the stickiness of a gecko’s toe.

The activities are as follows:

Species are able to do so many amazing things, from birds soaring in the air, lizards hanging upside-down from ceilings, and trees growing hundreds of feet tall. The study of biomechanics looks at living things from an engineering point of view to study these amazing abilities and discover why species come in such a huge variety of shapes and sizes. Biomechanics can improve our understanding of how plants and animals have adapted to their environments. We can also take what we learn from biology and apply it to our own inventions in a process called biomimicry. Using this approach, scientists have built robotic jellyfish to survey the oceans, walking robots to help transport goods, and fabrics that repel stains like water rolling off a lotus leaf.

Travis studies biomechanics and is interested in the ability of some species to climb and stick to walls. Sticky, or adhesive, toe pads have evolved in many different kinds of animals, including insects, arachnids, reptiles, amphibians, and mammals. Some animals, like frogs, bats, and bugs use suction cups to hold up their weight. Others, like geckos, beetles, and spiders have toe pads covered in tiny, branched hairs. These hairs actually adhere to the wall! Electrons in the molecules that make up the hairs interact with electrons in the molecules of the surface they’re climbing on, creating a weak and temporary attraction between the hairs and the surface. These weak attractions are called van der Waals forces.

Travis catching lizards in the Dominican Republic.

Travis catching lizards in the Dominican Republic.

The heavier the animal, the more adhesion they will need to stick and support their mass. With a larger toe surface area, more hairs can come in contact with the climbing surface, or the bigger the suction cup can be. For tiny species like mites and flies, tiny toes can do the job. Each fly toe only has to be able to support a small amount of weight. But when looking at larger animals like geckos, their increased weight means they need much larger toe pads to support them.

When comparing large and small objects, the mass of large objects grows much faster then their surface area does. As a result, larger species have to support more mass per amount of toe area and likely need to have non-proportionally larger toes than those needed by lighter species. This results in geckos having some crazy looking feet! This relationship between mass and surface area led Travis to hypothesize that larger species have evolved non-proportionally larger toe pads, which would allow them to support their weight and stick to surfaces.

To investigate this idea, Travis looked at the data published in a paper by David Labonte and fellow scientists. In their paper they measured toe pad surface area and mass of individual animals from 17 orders (225 species) including insects, arachnids, reptiles, amphibians, and mammals. From their data, Travis calculated the average toe pad area and mass for each order.

Travis then plotted each order’s mass and toe pad area on logarithmic axes so it is easier to compare very small and very large values. Unlike a standard axis where the amount represented between tick marks is always the same, on logarithmic axes each tick mark increases by 10 times the previous value. For example, if the first tick represents 1.0, the second tick will be 10, and the next 100. As an example, look at the graphs below.


The left plot shows hypothetical gecko species of different sizes, but with proportional toes. Their mass per toe pad area ratio (g/mm2) varies, with larger species having larger g/mm2 ratios. In this case, larger species have to support more mass per toe pad area. In the right plot, larger gecko species have disproportionally larger toes. These differences change each species’ mass per toe pad area ratios, so that all species, regardless of their size, have the same mass per toe pad area ratio.

Featured scientists: David Labonte, Christofer J. Clemente, Alex Dittrich, Chi-Yun Kuo, Alfred J. Crosby, Duncan J. Irschick, and Walter Federle. Written by: Travis Hagey

Data Nugget Flesch–Kincaid Reading Grade Level = 10.3

Scaling Up – Math Activity Flesch–Kincaid Reading Grade Level = 9.5

There is a scientific paper associated with the data in this Data Nugget. The data was used with permission from D. Labonte.

Labonte, D., Clemente, C.J., Dittrich, A., Kuo, C.Y., Crosby, A.J., Irschick, D.J. and Federle, W., 2016. Extreme positive allometry of animal adhesive pads and the size limits of adhesion-based climbing. Proceedings of the National Academy of Sciences, p.201519459.

To learn more about Travis and his research on geckos, read this blog post, “An evolving sticky situation” and check out the video below!

Sticky situations video

For a video and article on using “gecko power” to scale a building, check out this article – Climbing a Glass Building? Try a Gecko’s Sticky Pads

dr-fowleriAbout Travis: Ever since Travis was a kid, he was interested in animals and wanted to be a paleontologist. He even had many dinosaur names memorized to back it up! In college he discovered evolutionary biology, which drove him to apply for graduate school and become a scientist. There, he fell in love with comparative biomechanics, which combines evolutionary biology and mechanical engineering. Today Travis studies geckos and their sticky toes that allow them to scale surfaces like glass windows and tree branches.