Green Heron Observations

Green herons sit patiently and watch intently.  

Instead of thrashing around in the pond, sometimes it is better to just be still and quiet, waiting for an opportunity to arise. Like a fish swimming by. And then be ready to spring into action.

A green heron can move quickly and decisively when the time is right.

 

Green herons are also famous for using tools - dropping leaves or bugs into the water to attract fish, then picking up and repositioning the bait as needed. Very smart. I have only seen videos of this, though. Maybe the green herons I’ve watched have had plenty of fish and didn’t need to work that hard. 

 

Sometimes patience is all you need to catch a big fish.

Often people make up names that are meant to be descriptive but don’t really fit. There aren’t really many green feathers on a ‘green’ heron. To me their back and head feathers look more blue, and their necks are rusty red.

 

Those necks You can see better if you stick your neck out. 

And it can be convenient to just lean down and suck up a fish for dinner. 

But sometimes it’s good to blend into the background. Rusty striped neck and chest feathers can provide camouflage when the green herons are lurking by the edge of a pond.  

There are green herons that live in the Virgin Islands all year, and a few others that come down for the winter. The permanent residents live in the wetlands and make nests out of sticks, either on the ground or in trees. 

Usually the green herons keep their nests pretty well hidden. However, Laurel Brannick recently saw one with a nest in plain view, hanging out on a branch over the Francis Bay pond on St. John. 

Photo Laurel Brannick

The exposed location was probably not the best choice. Laurel thought she saw two chicks in the nest, but by the next week the nest was empty.  

Why Don’t Hermit Crabs Make Their Own Shells?

 

Hermit crabs have hard claws and legs, but soft abdomens they stick inside abandoned mollusk shells.

I enjoy having hermit crabs in the yard. They are known as soldier crabs in the Virgin Islands, but are not aggressive. They are generally cute and fun, and come by to snack on leftover cat food. 

Cats may not be so happy to see these intruders. But even if they catch a snacking hermit crab red-handed, they can’t do much damage to it when it's drawn up inside its shell. The hermit crab can stay inside its shell until the cat gets bored and leaves.  

 

Even when hermit crabs hide inside their shells, though, their legs and claws usually stick out some. As they grow larger, their legs and claws hang out further, and they have to start searching for a bigger shell.  

 

Recently I started to wonder why, after over 150 million years, hermit crabs are still scrounging around for discarded mollusk shells to cover their butts. 

 

Caribbean hermit crabs, or soldier crabs, (Coenobita clypeatus) commonly use cast-offs from West Indian Top Shells (Cittarium pica), otherwise known as whelks or wilks.

They are called ‘top shells’ because they resemble small spinning toys. 

 

West Indian Top Shells, like other marine snails, build an exterior exoskeleton through a process called biomineralization. They have an organ called a mantle that secretes a thin layer of protein as a base, followed by layers of calcium carbonate, which they create using carbon and calcium ions drawn from the seawater. The calcium carbonate then solidifies to make the hard shell. Later on, the mantle can add to the edge of the shell, so the same shell can grow as the snail gets bigger. 

Most crabs also use calcium carbonate to make hard shells for themselves that cover their whole bodies. But their shells are fitted to their legs and bodies, and not expandable. In a process called molting, as the crab grows bigger, it forms a new, thin exoskeleton cover underneath the existing shell, and breaks out of the old one. Once out, the crab then quickly makes the new, soft exoskeleton harder using calcium carbonate.    

 

Hermit crabs do the same kind of growing and molting as other crabs, but only their claws and legs get hardened up. The abdomen stays soft and the hermit crab needs to find a new larger shell to cover it. The shells provide protection from predators and also prevent them from getting dried out and cooking in the tropical sun. 

They do briefly take their shells off to mate. A male hermit crab will tap on a female’s legs to persuade her to come out and mate.   

 

Female hermit crabs make a group pilgrimage down to the shoreline to deposit their eggs in the water. There the eggs go through several free-floating phases of development before the baby hermit crabs start their transition to land. While in the water, they need to locate a discarded shell from a (dead) micro-mollusk, which are species of snails that remain tiny even as adults. Over time they will then work their way onto land and into ever larger shells.

Depending on finding abandoned shells from other dead animals seems pretty iffy as a life strategy, although it does allow successful hermit crabs to avoid spending a lot of energy building and maintaining their own mobile homes. They are renters, not owners, which in some situations can be an advantage. 

 

Still, the hermit crabs are heavily dependent on continued housing availability. There needs to be a large population of whelks – and intact shells left behind after they die or get eaten. In the Caribbean, an octopus or lobster will eat whelks, as well as bonefish, porcupinefish, and rock hinds. The whelks are also attractive to shorebirds like oystercatchers, which are locally known as whelk-crackers. And then there a number of people who collect whelks for stew. Supplies of whole, empty shells can quickly become limited. 

 

Hermit crabs are essentially recyclers, taking cast-off resources and reusing them, and in the process cleaning up the beaches. If they can’t find a shell that fits, they will sometimes end up wearing beach trash instead, which is a bit sad to see, but adaptive and enterprising of them. 

 

A hermit crab’s survival plan is also a bit poetic, as each temporary shelter it finds will carry a history of prior lives, which it will carry on its back, and then pass along.

 

 Small hermit crabs use shells other than top shells.