Tag Archives: Arthropods

I’m a rock. I promise. Please don’t eat me.

Noank, Connecticut

Spider crab, Libinia emarginata, Noank, Connecticut (4)
I’m a rock. I promise. Please don’t eat me.

I’m watching a rock shaggy with algae and mud and debris. I’m watching it eat. I’m watching it move. I’m watching it freeze solid when I slip my hand in the water. I look carefully through the water and pick out 6 more rocks that are not rocks. The cove is littered with rocks, both of ones that eat and ones that don’t. The rocks that eat are decorator crabs. This one is Libinia emarginata.

A decorator crab wouldn’t be get caught dead without wearing the ocean’s latest fashion. Actually, yes it would. Decoration for this crab not about fashion but survival. The more it looks like that rock or that coral or that plant over there the more it can rest easy that it won’t be on someone’s dinner plate. It just can’t help that it looks fabulous. All the time. This is a crab of confidence. One must be confident if it’s your clothes that determine whether you eat or get eaten. How might fashion be shaped if we judged outfits based on whether or not the model got scarfed up by a predator at the end of the runway? A new ‘reality’ show? (I’ll leave it to you to come up with a clever title for this new reality show. Go ahead, whisper you clever little gem to me.)

Libinia emarginata (5)

Decorator crabs are found in variety of habitats including kelps, estuaries, and corals and use whatever’s available to be en vogue. It is a major fashion faux pas to show up to a new event in a new habitat wearing old clothes. A crab placed in a new habitat will shed its old outfit and immediately use local materials to blend in (even an aquarium full of pearls and lace – see video below; called a ‘dresser crab’ by the British). A bit of shaggy algae here, a dab of lace there.

The decorator crab I’ve been watching is also known as a spider crab. All decorator crabs are spider crabs, but not all spiders are decorators. This family brags not only the most fashionable crabs, but also the largest – the 12-foot Japanese spider crab, Macrocheira kaempferi. This crab is not a decorator crab. Perhaps when you’re more leg than body and can stretch up to a second story window (if you’re on your crab tippy toes), then you are either not worried about being someone’s dinner or perhaps you don’t think you’d make a convincing plant.

Japanese spider crab, Image courtesy of dailymail.co.uk

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The savory swimmer swims north?

A blue crab (Callinectes sapidus) found north of Cape Cod in 2012. Plum Island Estuary, Massachusetts
A blue crab (Callinectes sapidus) found north of Cape Cod in 2012. Plum Island Estuary, Massachusetts

In the summer of 2012 I was having dinner with colleagues when one offhandedly said that he’d seen a blue crab, Calinectes sapidus in the marsh (the Great Marsh in northeast Mass.). Incredulous, I said a more colorful version of, “Equine feces.” He was claiming that a blue crab was in the Great Marsh, far north of its northern limit of Cape Cod.

Then other sightings of blue crabs in the Great Marsh were reported.

I grabbed a long-handled net and walked the tidal creek bottoms. I saw many green crabs scuttle but then, in a deep pool, I saw a crab swim sideways and instantly knew it was a blue crab (blue crabs are in the family Portunidae which are swimming crabs with flattened back legs). I found three more that summer.

Finding a blue crab in the the Great Marsh was surprising because the marsh lies in the Gulf of Maine which extends from Cape Cod to Canada and is kept cold by cold water currents from Canada. Water too cold for blue crabs.

Using the list-servs, Twitter and colleagues I crowd-sourced information about observations of blue crabs throughout the Gulf of Maine and from 2012 – 2014 these often-called ‘Maryland’ crabs were found as far north as Maine and Nova Scotia. The reason? I hypothesize warming oceans. Water temperatures in 2012 and 2013 were much warmer than the average of the previous decade which may have lowered the temperature barrier. Earlier I reported on a similar range extension for the fiddler crab.

Solid line: historic blue crab distribution. Dashed line: potential new range extension.
Solid line: historic blue crab distribution. Dashed line: potential new range extension. Arrows indicate sightings of crabs from 2012-2014.

It may be a logical fallacy to talk about climate change and warming seas when Boston is undergoing record snows (record-breaking snows are consistent with climate-change theory as warmer air holds more moisture prior to storm events), but we cannot deny that the climate is changing. One prediction of climate change is that as the climate and oceans warm species will start shifting where they are found. We’ve seen this already in many commercial species such as hake, flounder, and lobsters in the northeast where the concentration of their biomass has shifted north. The Connecticut lobster fishery (CT the southern end of the lobster’s distribution) is severely depleted, possibly in part to lobsters moving north.

What makes my observations of blue crabs north of Cape Cod unique is that this is the first time a commercially important species has been reported to potentially expand into the Gulf of Maine. It should be noted that in the past 150 years there have been four other reports of blue crabs in the Gulf of Maine, but none of those populations were permanent. It’s still to be seen if the 2012 blue crab population is a permanent extension of their range. If so, then it means that crab cakes are expanding north thanks to climate change.

The blog’s title? Callinectes sapidus means ‘savory swimmer’.

The article can be found here: The savory swimmer swims north: a northern range extension of the blue crab Callinectes sapidus?

To freeze or not to freeze?

Newbury, Massachusetts The Great Marsh

Coffee-bean snail and wolf spider, Newbury, Massachusetts
Coffee-bean snail and wolf spider, Newbury, Massachusetts (don’t ask me why the colors look the way they do).
Thin-legged wolf spider, Pardosa littoralis, Newbury, Massachusetts
Thin-legged wolf spider, Pardosa littoralis, Newbury, Massachusetts

I had to close my eyes to the spray of ice as I slammed the claw hammer into the 3-inch ice that armored the marsh.  I use the claw to peel back ice chunks and hunt for life.  Ten minutes later I find two winter denizens of the Great Marsh.  I de-glove and carefully remove a thin-legged wolf spider (Pardosa littoralis) and a coffee-bean snail (Melampus bidentatus) from the grass stems.  They are not dead, but possibly as near as you can get.  Their organs are slowed, their metabolism at a glacial crawl.  They are, for now, frozen in time.  One of them quite literally (and I mean ‘literally’, not ‘figuratively’). All overwintering animals, including you and me and your little brother, have two choices when it comes to surviving the winter.  Freeze avoidance or Freeze tolerance.  Freeze avoidance usually means finding a shelter for the winter (called a hibernaculum) such as a burrow below the frost line or a shelter with a thermostat cranked to 72 F and stocked Rolos and oatmeal chocolate chip cookies (no.  not raisins.  raisins belong in only two places:  bran and the trash).  Freeze tolerance usually means that you’ve got to freeze some-to-most of your body.  Some frogs and salamanders and many intertidal molluscs (snails, clams) do this.

The coffee-bean snail shivered so I gave him some coffee.  He took a sip and looked up at me, "Wait, what is this made of?"
The coffee-bean snail shivered so I gave him some coffee. He took a sip and looked up at me, “Wait, what is this made of?”
Coffee bean snail on Dunkin Donuts cup
I will avenge you my brothers and destroy the Evil Empire!!!!! Your slow-roasted deaths shall not be in vain!

But what’s wrong with freezing?  The biggest issue with freezing has to do with ice crystals that form and ice that expands.  Ice crystals are assassins that form inside the cell and use their stiletto-sharp crystals to rupture and kill cells.  So whether you’re a freeze avoider or a freeze tolerator, your imperative is to protect your cells.  Too many dead cells equals one dead you.   Both the snail and spider are freeze avoiders in terms of their behavior:  in the winter they are ‘snuggled’ together under grass clumps that are slightly warmer than the surrounding air.  In terms of their internal physiology, the snail is a freeze tolerator and the spider is a freeze avoider.

Avoiding the freeze
Many insects and spiders (not all) produce anti-freeze compounds (some insects actually produce the same anti-freeze we use in our cars, ethelyene glycol), which lowers the freezing point of their body fluids.   At the same time, they will dump sugars into their body fluids which also lowers the freezing point (anytime you dump sugars or salts into water, it lowers it’s freezing point).  So when it’s 18 F, the spider still won’t freeze though freshwater will.  If I hold this spider in my hand long enough or bring him inside, he will eventually start crawling around (though he’ll be really confused and very hungry).    

Tolerating the freeze
The snail actually freezes part of the body to save the rest.  Part of the fluid outside of the cell (extracellular fluid) freezes which forces body salts into the liquid part of the extracellular fluid.  This creates an osmotic gradient with higher salt content outside of the cell versus inside the cell.  Because Nature seeks balance, the water inside the cell moves out of the cell until the salt levels are equal in and out of the cell.  This cell dehydration then increases the salt content of the cell, which in turn lowers the freezing point of the cell.  Again, saltier or sugarier solutions have lower freezing points  than freshwater solutions.

Wood frogs (Rana sylvatica) perform a similar feat and people have claimed to have found ‘frog-sicles’ under logs.  The take-home is that the frog, just like the snail, is not completely frozen.  It can’t be or it would die.  It may, however, be mostly frozen (up to 65% of it’s body liquid) to protect the cells.  Most of the cells inside are not frozen despite that fact that the soft bodies of snail and the frog are now hard as rocks.

In both freezing strategies, animals are trying to protect their cells and do so by lowering the freezing point of some portion of their body.

We humans do something similar so we can salt icy roads.  The salt melts the ice because it’s lowering the freezing point of water.  The first guy to do this probably thought he was pretty clever.  The coffee-bean snail would shake his head and say, “no, no you’re not.  i’ve been doing it for millenia.”  Then the clever guy would say, “Holy crap!  A talking snail!”

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Thanks to Duley for spending more time than either of us should have trying to craft the perfect snail jokes.   And perfect they are!

Why my grasshoppers are cooler than yours.

Hilliard, Florida
Thanksgiving weekend

Nephew Logan and I on the hunt.
Grasshopper view of Nephew Logan on the hunt.

Nephew Logan and I were on the hunt for grasshoppers in a field surrounded by tall and scrawny black pines with an underskirt of saw palmettos.  Nephew Logan (7) is not keen on actually touching any grasshoppers, but was okay holding the plastic water bottle that we shoved them in.  As the grasshoppers popped like popcorn in the plastic bottle, he diligently checked to make sure the lid was tight.  Can’t let a grasshopper escape, it might touch you!

We found at least four different species of grasshoppers.  Nephew Logan was not terribly impressed by that diversity; he wanted to feed the grasshoppers to the chickens (another critter he’s not keen to touch).

The pines of Hilliard
The pines of Hilliard

Grasshoppers aren’t easy to catch.  Mostly because you can’t see them until they fly or hop away.  In the world, you are the eaten or the eater, and grasshoppers are trying not to be the first one.

Grasshoppers, being the clever creatures that they are, have numerous strategies to evade being a snack for a bird or a snake or an Uncle David (Oh, I’ve had grasshopper before).  As a first line of defense, most grasshoppers use crypsis to avoid from being seen (but see my note below about aposematic coloration).  Crypsis is blending into your environment so you can’t be seen.  This is typically via camouflage, but some engage in mimicry to look like something that you don’t want to eat (think about walking sticks).  

 And that’s what this guy does.   

This is the long-headed toothpick grasshopper, Archurum carniatum, and he’s the coolest grasshopper in the whole wide world.  Yup.  Whole wide world.  I challenge you to find a cooler dude.  Look at him! Isn’t it amazing how his tan, slender body  looks just like the dead grass surrounding him?  And look at the picture closely and you can see the black specks on his body that mimic the fungal spots found on the dying grass!  There’s even a black speck on his little eyeball!  What a fantastic adaptation!  This grasshopper doesn’t fly and isn’t a strong jumper.  His entire strategy is, “You can’t see me, you can’t see me.  I’m grass.  See?  No you can’t because I’m grass!”  I only saw our long-headed friend when Nephew Logan’s sweeping foot forced him to jump.

Second place in the coolest grasshopper in the whole-wide-world category goes to the American bird grasshopper, Schistocerca americana.  He relies on camouflage, but when a predator or nephew gets too close he flies 30-foot high into the tall pines.  His strategy of predator avoidance is to fly as far and as high as possible and then once landed, blend into the tree.  These grasshoppers are huge – as long as my finger – and look like small, awkward birds when they fly.  I was only able to catch one though we flushed many.

Later in the day, Brother Cody (17) and I were able to catch another species of bird grasshopper (the obscure bird grasshopper Schistocerca obscura) in a different field as we talked at length about girls (I was hoping he had some advice for me.  He did not.).

Two grasshoppers.  Same field.  Two very different strategies.  Both of which are effective against one Uncle David and one Nephew Logan.

One strategy we didn’t see, though you certainly can in Florida, is what is called ‘aposematic coloration.’  This is the opposite of crypsis.  You want to be seen.  Aposematic coloration involves bright color markings on the body as a warning to say, “Hey!  If you eat me I’ll mess you up!”  Think of the brightly colored coral snakes or poison dart frogs.  These aren’t prima donnas showing off like a peacock.  These are advertisements of death!  Below is a picture of a grasshopper with aposematic coloration.  

Happy hopper hunting!

Okay, this dude is pretty cool too. Not my pic. Original can be found here: http://www.flickr.com/photos/80125969@N00/499771069