Tuesday, September 29, 2009

Spiders doing a mating dance in the garden

I wasn't planning on writing another entry for "creepy-crawly week," but on Saturday I saw something in the garden that could not be ignored.

As I was walking across the yard, I noticed some motion in one of the cross spider (Araneus Diadematus) webs. It was another spider, one much smaller than the resident of the web, both in span and volume, carefully flitting to the bigger spider, engaging a little, and then moving back, while also strumming on the web with its front legs*. Based on this behavior I realized that it must be the male spider trying to mate with the female. It's not an easy task, given that spiders will eat pretty much anything they can catch.

Knowing that the mating act for some spiders is a cannibalistic one — the female eats the male after mating — I had a great title for the post picked out, something along the lines of "Finding love in the garden, followed by death."

But a little bit of research at the Encyclopedia of Life wiped out my title.  The entry for Araneus Diadematus has this about that species' mating habits:
Males approach females with caution in order to avoid being eaten. During copulation, males embrace the female's abdomen; sperm is transferred by the insertion of one of the male's palps. The male departs after mating, and the female spends a number of days inside her retreat. She then begins to spin an egg sac or 'cocoon', which protects the eggs. She stays close to the cocoon for a number of days before dying.
I checked back on the spider pair a few more times on Saturday and Sunday to find that the male was still hanging around while the female was perched under a leaf, perhaps resting in "her retreat," preparing for her egg sac spinning.  Or perhaps tired of the male's advances and web music.

One of the spiders that practices post-mating cannibalism is the Australian redback spider (a member of the black widow genus, Latrodectus). Earlier this summer, PBS's scienceNOW had a profile of biologist Maydianne Andrade (full video available for streaming or download), a patient and daring researcher who does her fieldwork at night in the Australian forest. Her quarry is the redback, one of the most poisonous spiders on the planet. One of the big questions she is investigating is "why does this spider practice cannibalism?"

Not surprisingly, Andrade's research shows that there is some evolutionary logic to cannibalism during mating:  by allowing itself to be eaten by the female, the male redback can spend just a little bit longer in the mating position, thereby improving the odds that his genes will be passed on to the next generation. And in any case, if he isn't eaten by a female, he'll probably be eaten by ants or starve to death (if that didn't happen already — most males never find a female).

* In 2007, Living on Earth had a segment about spider songs, with audio available for streaming or as an MP3 download.

Random link from the archive: Technological Optimism and Pessimism
Technorati tags: Spiders : Nature

Friday, September 25, 2009

Parasites are creepy -- and also amazing

It seems to be creepy-crawly week here at Mental Masala, with today's installment covering parasites.  Radiolab, a fascinating radio program from WNYC (and available for download via iTunes and other podcasting software), recently devoted their show to parasites. It had the story of zombie roaches, how eliminating hookworm in the southern U.S. helped improve economic productivity, the unexpected tale of how one man infected himself with a hookworm parasite in a desperate attempt to cure his allergies (he says that it worked), and, of course, some audio from Alien (you can probably guess which part).

David Attenborough's Life in the Undergrowth (which I've mentioned at least twice before) has a parasite story that is so amazing that it's hard to believe it is true. The six-minute, third-two second segment is on-line at YouTube and should be embedded below.

The key to the success of the caterpillar and the wasp is chemical signaling — the caterpillar smelling like an ant larva and wasp causing ants to turn on their nest-mates. Humans can also sometimes exploit these chemicals. A 2006 story in the San Francisco Chronicle tells of research on the chemical signals used by Argentine ants (the bane of many a Californian), with one of the goals being discovery of a chemical that will cause the ants to attack each other (perhaps by making them smell like invaders). Another interesting story about ants and chemicals can be found in one of Radiolab's short pieces, a conversation between host Robert Krulwich and legendary entomologist E.O. Wilson. Wilson tells of some of his ant experiments, including a rather devious one where he dabbed ants with the chemical given off by a dead ant. When a worker detects the 'dead ant scent,' it carries the corpse out of the nest to the trash heap. And so, the live ant got the same treatment and was carried out of the nest several times until it was able to clean itself.

Random link from the archive: Recipe - Roman style carrots

Technorati tags: Insects : Ants : Nature

Monday, September 21, 2009


These line drawings aren’t some kind of code or ancient writing, they represent spider webs that have been  in my backyard in recent days. The circle represents the web and the radiating lines represent the support structures.  At the center of the circle is a dot that represents the 1-cm diameter spider (probably a cross spider, Araneus Diadematus), but because the web and its supports are so large, the dot is vanishingly small. 

The right-hand figure shows a 25-cm diameter web supported by a 300 cm (~10 ft) line on the side, a 250 cm (~8.2 ft) line to the ground, and multiple short pieces on the left. In other words, the spider is about 250 body lengths above the ground. To put it in human terms, it would be like a 1.82 m (6 ft) person perched on a very fine net that was 455 m (1,500 ft) above the ground. It's somewhat like Philippe Petit's wire-walk between the two towers of the unfinished World Trade Center towers in 1974, which was just over 400 m (1,300 ft) tall. His walk — and the complicated preparations that it required — were vertiginously and beautifully documented in Man on Wire (and also in a book of the same name).

To return to spider terms, they probably don't get vertigo and don't realize how far they are from the ground or nearby objects. From what I've seen and read, web-building spiders are creatures of vibration and the near-field:  they respond to things hitting their web and what's very close-by. So hanging out a few hundred body-lengths from a solid object is no big deal...

The left-hand figure has support lines that are 150 cm (4.92 ft) long. In other words, the spider is over 150 body lengths from the nearest solid object. That's like 1.82 m (6 ft) person on a very fine net 274 m (900 ft) above the ground and with 274 m between you and the nearest object on either side.  For reference, the Chrysler Building has a height of 319 m, the Empire State Building 381 m, and the Transamerica Pyramid 260 m.

How can something so small create a web that spans such a huge distance? It works something like this: while perched on an object above ground, the spider lets a long piece of silk be carried by the wind until it catches on something (like a nearby tree). Next, the spider pulls the line tight (and might even traverse the line while laying another line to increase the strength of the upper support). It then outside support by walking back across the line while time dropping a line of silk below the main line to make a rotated D-shape (with the straight side on top). Next, it crawls down the loose piece until it reaches the middle, then it drops down to the nearest object and pulls the line tight to turn that D into a Y. Thus, the basic frame of the web is made. From that point, it is a matter of placing radial lines, then laying the spiral. Howstuffworks has a series of illustrations that demonstration how a spider weaves an orb web.

For more about spiders, check out David Attenborough's "Life in the Undergrowth." It's filled with amazing footage and stories from the world of insects, arachnids, slugs and other invertebrates.

The Man on Wire image is from Wikipedia, which claims that this particular image is covered under the Fair Use provision of copyright law. The photo and line drawing are by the author.

Friday, September 18, 2009

Recipe: Ersatz South Indian rice with yogurt

Another quick way I've been using curry leaves lately is in a dish of spiced rice and yogurt, which is sometimes called "curd rice." The idea and basic spicing comes from Dakshin: Vegetarian Cuisine from South India by Chandra Padmanabhan (one of my favorite Indian cookbooks). The steps are simple:  cook some rice, add chopped vegetables (cooked or raw, depending on the vegetable), fry spices in oil, mix the oil and spices with the rice, then serve with plenty of plain yogurt.

Recipe: Ersatz South Indian rice with yogurt


3 cups cooked basmati rice
1 cup vegetables: fresh tomatoes, cooked carrot, cooked peas, sauteed onion, fresh chilis, etc.
Salt to taste
Plain yogurt
Roasted peanuts or cashews, coarsely chopped (optional)
Fresh cilantro, chopped (optional)
Cooking oil

1 t. brown mustard seeds
1 t. cumin seeds
2 t. black gram dal (washed urad dal), picked over, rinsed, and well dried (see note)
2 t. chana dal, picked over, rinsed, and well dried (see note)
1 dried red chili
1/2 t. asafoetida powder
6-12 fresh curry leaves, washed and well dried

Combine the mustard seeds, cumin seeds, dals, chili asafoetida, and curry leaves in a small bowl and set aside.

Gently mix the vegetables into the cooked rice. Add salt to taste.

Before cooking the spices, have a pot lid handy in case the mustard seeds splatter violently.  Heat about 1 tablespoon of cooking oil in a small skillet over high heat. When hot but not smoking, add the spice mixture and shake the skillet to distribute.  Cook, stirring or shaking the pan, until the mustard seeds pop (usually under a minute), then pour over the rice. Gently distribute the spices through the rice.

Garnished with the optional cilantro and chopped nuts, and serve with plenty of plain yogurt.

Note: I usually wash and dry enough dal to make several recipes.  First I thoroughly rinse the dal in a sieve, shake off excess water, and then spread them onto a cookie sheet.  My oven has a pilot light, so I put the pan into the oven for a few hours, moving the dal around on the sheet every now and then to fully dry them. After they have cooled, I store them in glass jars in my spice cabinet.

Random link from the archive: Recipe - Thai coconut, galangal and cauliflower soup
Technorati tags: India : rice : vegetarian : Food

Wednesday, September 09, 2009

Afternoon Tea in the Laboratory: Part 2

A few weeks ago, I reviewed an academic paper on tea brewing — how brewing technique and tea brand affect caffeine and dissolved solids levels. In that paper, the authors demonstrated that the highest level of dissolved solids (which correlates with flavor and possibly anti-oxidants) come from loose leaves or a well-agitated tea bag, and that caffeine pours out of the tea most quickly in the early moments of brewing.

During the search for academic papers about tea brewing that led me to the previously reviewed on, I ran across an impressive body of work by Michael Spiro, Deogratius Jaganyi, and several colleagues that spans several decades. While working at the University of Natal (South Africa) or the Imperial College of Science, Technology and Medicine (London), they have published at scores of scientific papers on the subject of tea, including a 15 part series on "kinetics and equilibria of tea infusion." (The word "kinetics" in this context refers to transfer or reaction rates — e.g., how fast is caffeine extracted, how chemical reactions progress. The word "equilibria" refers to the end state of the brewing process — after a long time, what is the stable configuration.)

Spiro and Jaganyi's 1992 paper in Food Chemistry is only a few pages, but contains a lot of insights into tea brewing, so I'll use it to as the main resource. Having the unwieldy title of "Kinetics and equilibria of tea infusion: Part 9. The rates and temperature coefficients of caffeine extraction from green Chun Mee and black Assam Bukial teas," the article explores how brewing temperature affects caffeine concentration. To explain their findings, I've taken their measurements and modeling and created new charts.*

Time, Temperature and Color
This first figure shows Spiro and Jaganyi's measurements and calculations for black tea at three different temperatures (using 4 grams of tea leaves and 200 cm3 of distilled water). The x-axis is time — how long has it been since water was poured over the tea — and the y-axis is the concentration of caffeine in the water (in millimoles per cubic decimeter). The black diamonds are the actual measurements made in the 80 °C experiment; the lines are calculations of caffeine concentration the well-established mathematical model** presented in the article for 70, 80 and 90 °C water (158, 176, and 194 °F). Although the curves show non-zero caffeine concentration at time zero, that is an artifact of the mathematical model, not representation of real behavior.

A few things are readily apparent in the chart. First, for reasonably short brewing times hotter water means more caffeine. For a four minute brew, for example, increasing the water temperature from 80 to 90 °C increases the caffeine content by 36%. Second, for the lower brewing temperatures, the caffeine rises almost linearly during first few minutes, so increasing the brewing time will significantly increase the caffeine level. For instance, lengthening the brew time from 3 to 5 minutes at 70 °C ups the caffeine level by 26%. Third, for water at nearly the boiling point, almost all of the caffeine is extracted in a few minutes: at 90 °C increasing the brewing time from 3 minutes to 5 minutes adds only 13% more caffeine. Fourth, given enough time, the caffeine content will be independent of the brewing temperature — the system will reach an equilibrium point where all of the available caffeine will be extracted from the tea leaves***. However, according to many tea experts, all sorts of unpleasant flavor compounds will also be extracted.

The paper also has data for green tea, which shows similar behavior: hotter water leads to more caffeine, most of the caffeine is extracted in the first few minutes, and so on.  The equilibrium level for caffeine is quite a bit lower: the teas used in the study have equilibrium caffeine concentrations of 2.7 vs. 4.2 millimoles per cubic decimeter for green and black tea at 90 °C and 92 °C, respectively.)

Brewing while the Water is Cooling
This is all interesting, but what happens in a tea pot at home is not what happens in the lab. In many home tea pots (or the Pyrex measuring cup that I use), the water temperature decreases during brewing. I measured mine and found a 46 °F (25 °C) drop over 5 minutes (I have since started covering the measuring cup when brewing tea to reduce heat losses).

The first figure showed a strong dependence of caffeine extraction on temperature, so as water temperature drops, we would expect less caffeine to be extracted. In other words, the "rate constant" decreases.  Using data in the paper and my kitchen measurements, I was able to write an equation that gives the caffeine concentration over time as the temperature of the water decreases.  The next figure shows the results. The smooth curves are based on the data in the Spiro and Jaganyi paper; the large black arrows illustrate what is happening as the tea brews while the water cools. The first arrow shows the approximate progression during the first minute: from zero caffeine to a level that corresponds to water at about 85 °C. In the next minute the temperature drops to 80 °C, and so the arrow progresses at a slightly lower slope. Over the next three minutes the temperature continues to drop, with a final temperature of about 75 °C. My calculation results in approximately 3.3 mmol/dm3 of caffeine, quite a bit less than what one would obtain from a brew at a continuous 90 or 100 °C (about 4 mmol/dm3).

Summing Up
To sum up, the highest rate of caffeine extraction is in the early part of the brewing, higher temperatures lead to higher caffeine levels, and heat loss during brewing will reduce the overall caffeine content. So, for the most potent cup of tea without without brewing for so long that unpleasant flavors are extracted (e.g., 15 minutes), use the hottest water possible and minimize heat losses during brewing.

* A question about chart making:  I make my charts in Excel, take a screen capture, crop in Picasa, export, and then upload to Blogger. During this process, lines lose clarity. Is there a better way to get a chart into Blogger?

** The concentration of caffeine at any time can be expressed as ln [ c / (c - c) ] = k t + a, where c is the current caffeine concentration, c is the caffeine concentration at equilibrium, t is time, k is the rate constant, and a is the intercept. In the paper described above, k and a were determined using linear regression of the experimental data.

*** I'm skeptical that caffeine will reach equilibrium levels in a reasonable amount of time at low temperatures, such as in a refrigerator, but my only evidence is anecdotal. A few years ago, inspired by a segment on The Splendid Table, I tried a cold brewing method  — where you add tea leaves to cool water and let it sit in the refrigerator overnight. During that short-lived experiment, I was incredibly tired, dozing off in the afternoon. My guess is far less caffeine was dissolved in the cool water than for my usual brew.

Random link from the archive: Edible Communities

Technorati tags: Tea : Drinks : Caffeine

Sunday, September 06, 2009

Mosquitoes in Siberia

In two recent issues of the New Yorker, staff writer Ian Frazier describes a four-thousand mile trip across Siberia. So far, because of my haphazard system of New Yorker consumption (read "Talk of the Town" and an article or two, then add it to the pile), I have only read Part II and am not sure where Part I is.

Western Siberia is mosquito country. I grew up in a place with plenty of the buzzing pests, but nothing like what he experienced:
The country's swampiness did not manifest itself in great expanses of water with reeds and trees in it, like the Florida Everglades. There were wide rivers and reedy places, but also birch groves and hills and yellow fields. The way you could tell you were in the swamp was, first, that the ground became impassably soggy if you walked at all far in any direction; and, second, by the mosquitoes.

I have been in mosquito swarms in beaver meadows in northern Michigan, in boreal wetlands in Canada, and near Alaska's Yukon River. Western Siberia has more. On calm and sultry evenings as we busied ourselves around the camp, mosquitoes came at us as if shot from a fire hose. Usually mosquitoes cluster in a cloud around their targets, but as Volodya made dinner I observed a thick and proximate cloud surrounding him head to toe, and then a whole other sort of candidate swarm around that inner swarm, and then more in all directions, minutely enlivening the sky.

The full article is unfortunately not on-line at this moment for non-subscribers (abstract only), but might show up someday.

Random link from the archive: On Growing Vegetables as Ornamentals