Category Archives: Invertebrates

Our blood too rich

mosquito_cropped

I choose today, when most of us in New England are sunk under wet snow and dreaming of the hot, humid days of summer, to remind you that every season has its dark side.  When the sun is beating down on us and moisture in the air suppresses our every movement, we will fall prey to a ubiquitous pest that everyone recognizes: the mosquito.  Last year’s wet spring left plenty of standing water for breeding, and the resulting swarms were, in some places, intolerable.  But why do these insects behave the way they do?  How do they find us?  Why do they require our blood?

First came the scouts who felt our sweat in the air
and understood our need to make a sacrifice.  
 
We were so large and burdened with all we had carried
our blood too rich for our own good.  
 

Alison Hawthorne Deming’s poem, “Mosquitoes,” examines the interaction between mosquitoes and humans in a slightly different viewpoint than we are used to.  Most often, humans view mosquitoes as pests, disease-bearing annoyances that inhibit our enjoyment of the outdoors in summer.  Instead, the speaker in this poem views us as a sacrifice, burdened with rich blood ripe for the taking.

There are over 2,700 species of mosquitoes in the world, and all of them require water to breed.  Most eggs overwinter and hatch into larvae in the spring.  Larvae eventually grow into pupae, which after one to four days form a pupal case, within which they metamorphose into adult mosquitoes.  Their purpose now is to mate and feed.

Female mosquitoes are the attackers.  (Males live only a few days after mating, surviving on plant nectar.)  Protein obtained from ingesting blood aides the female in development of eggs.  The mosquito requires a blood meal each time she lays eggs, and can live anywhere from days to weeks, repeating the process of feeding and laying eggs many times.  The eggs hatch or overwinter; the cycle resumes.

Then came the throng encircling our heads like acoustic haloes
droning with the me-me-me of appetite.
 

Several factors have been shown to attract mosquitoes, including: perspiration, heat, light, body odor, lactic acid, and carbon dioxide.  When a female lands on a likely victim, she sucks blood with her proboscis, or feeding apparatus.  There are actually six mouthparts contained in the female’s needle-like proboscis.  The outer sheath is the labium, which bends back to allow the two pointed mandibles and two serrated maxillae to penetrate the skin.  Mosquito bites are generally not very painful because the jagged shape of the maxillae results in a low surface area and a minimum of contact with nerves in the skin.  On the basis of this finding, a Japanese scientist has recently designed a nearly-painless hypodermic needle modeled after a mosquito’s maxilla.

Once the maxillae and mandibles have entered the skin, the mosquito pumps her own saliva into the wound through a hypopharynx, while the tubular labrum allows her to suck blood into her own abdomen.  The saliva contains an anticoagulant, ensuring that blood flow is continuous through the meal.  Itching after a bite is due to our natural immune response to the mosquito’s saliva.  Even after the swollen wheal disappears, the itch remains until your body has broken down the proteins in the saliva.

We understood their female ardor to breed and how little
they had to go on considering the protein required to make
 
their million-fold eggs.  Vibrant, available, and hot,
we gave our flesh in selfless service to their future.  
 

So think of this as you complain about winter.  Remember that summer is coming, and with it, the mosquitoes.  Prepare yourself as a sacrifice.

REFERENCES:

Coxworth, Ben.  04.04.2011.  “Mosquito inspires near-painless hypodermic needle.”  Gizmag.com

Darsie, RF, Jr. and RA Ward.  1981.  Identification and Geographical Distribution of Mosquitoes of North America, north of Mexico.  Fresno, CA: American Mosquito Control Association.

Freudenrich, Craig.  “How Mosquitos Work.”  Howstuffworks.com

“Mosquito Biology.”  Alameda County Mosquito Abatement.  Link. 

“Mosquitoes.”  Alison Hawthorne Deming.  Read it here.

Sutherland, DJ.  2013.  “Mosquitos in Your Life.”  Rutgers School of Environmental and Biological Sciences: Department of Entomology page.  Link. 

Ever unreeling

spider

Few creatures inspire so much instinctive fear as the spider.  Perhaps it is the number of legs.  Or the rotund, hairy bodies.  Or the knowledge that some are poisonous to us, without the understanding of which species pose a threat.  Perhaps it is simply the alien nature of their existence: how they can be unseen and everywhere, so different from us, so impossible.

In the first stanza of Walt Whitman’s poem, “A noiseless patient spider,” the author observes the behavior of a spider as it throws out one silken thread after another:

“A noiseless patient spider,
I mark’d where on a little promontory it stood isolated,
Mark’d how to explore the vacant vast surrounding,
It launch’d forth filament, filament, filament out of itself,
Ever unreeling them, ever tirelessly speeding them.”
 

We’ve all seen a spider dangling inexplicably from the ceiling, or watched it escape on its line of filament.  But how does a spider create silk?  Where does this material come from, and why is it so strong?

As it turns out, spiders have seven different kinds of silk, produced by seven silk glands.  One spider cannot make all seven types of silk; instead, males have at least three different types, and females have at least four.  These glands secrete silk proteins (made of strings of amino acids) dissolved in solution.  Liquid silk is pushed through internal ducts and emerges from microscopic spigots on the spider’s spinnerets (organs at the rear of the spider’s abdomen, designed for just this purpose).  This electron micrograph shows the silk spigots in operation:

Image by MicroAngela

Image by MicroAngela

There is a valve on every spigot that controls the speed and thickness of the silk.  As the spigots exude silk, they pull fibroin protein molecules from the ducts.  With the addition of these protein molecules, the silk becomes stretched out and the molecules link in the air.  The spinnerets wind the strands together to become a silk fiber.  Spider silk is incredibly tough and is stronger by weight than steel.  Some varieties are twice as strong by weight than Kevlar, the toughest man-made polymer.

So what have we done to harness this natural resource?  As early as 1710, a Frenchman, François Xavier Bon de Saint Hilaire, showed Europeans how garments could be made from spider silk.  Recently, an entire golden cape (the natural color of the silk) has been created…with the help of 1.2 million spiders.  Companies have also tried to harness the almost supernatural strength of spider silk, though the problem has always been producing enough in quantity.  A company called Nexia successfully created transgenic goats that could produce spider silk proteins in their milk.  Even that wasn’t enough for mass production, and the company went bankrupt in 2009.  Most recently, in 2012, Dr. Craig Vierra demonstrated techniques to develop and process synthetic spider silk from bacteria.  So the search goes on.

Was Whitman thinking about any of this when he wrote “A noiseless patient spider”?  I doubt it.  But he was, apparently, thinking of how humans are not so different from spiders after all.  Spiders spin their tenuous thread to find their way in “the vacant vast surrounding.”  Whitman recognizes this behavior in his second stanza:

“And you O my soul where you stand,
Surrounded, detached, in measureless oceans of space,
Ceaselessly musing, venturing, throwing, seeking the spheres to connect them,
Till the bridge you will need be form’d, till the ductile anchor hold,
Till the gossamer thread you fling catch somewhere, O my soul.”
 

In a literal sense, humans build bridges to get from one place to another, planes and cars and buses to carry us there.  But do we not all seek a place?  Do we not seek knowledge and experience and try to understand our surroundings?  Whitman’s soul is doing its best to find a place where he can anchor.  He is casting out his “gossamer thread” and praying it will catch, hoping to be no longer lost in “measureless oceans of space.”  It seems we have much to learn from spiders, perhaps more than we knew.

REFERENCES:

Harris, Tom. 2002. “How Spiders Work”  HowStuffWorks.com. Link.

Jones, Denna.  2012.  “The gossamer cape: spun by a million spiders.” The Guardian.  Link.

The Journal of Visualized Experiments. “The future of biomaterial manufacturing: Spider silk production from bacteria.” ScienceDaily, 18 Jul. 2012. Link.

“A noiseless patient spider,” by Walt Whitman.  Read it here.

O’Brien, Miles and Marsha Walton.  2010. “Got Silk?”  NSF Science Nation.  Link.