Category: crustaceans

45 million red crabs migrate to the sea

November 8, 2024 • 12:30 pm

To end, the week, we have some stunning videos from BBC Earth and other places, depicting the migratory behavior of the red crabs of Christmas Island, a small Australian territory (135 km², pop. 1692 ) near Indonesia: encircled below. Their vernacular name is The Christmas Island red crab, the Latin binomial is Gecarcoidea natalis, and they are  endemic to that island and the Cocos (Keeling) Islands in the Indian Ocean.

TUBS, CC BY-SA 3.0, via Wikimedia Commons

The life cycle of this crustacean is described here, but the videos are more impressive. Here are the basic facts:

The migration starts with the first rainfall of the wet season. This is usually in October or November, but can sometimes be as late as December or January.

Red crabs all over the island leave their homes at the same time and start marching towards the ocean to mate and spawn. Male crabs lead the migration and are joined by females along the way.

The exact timing and speed of the migration is determined by the phase of the moon. Red crabs always spawn before dawn on a receding high-tide during the last quarter of the moon. Incredibly, they know exactly when to leave their burrows to make this lunar date.

However, because crabs wait until the first rainfall to start their trek, they sometimes have to hurry. If the rains arrive close to the optimal spawning date, they will move rapidly. But if the rain comes early they may take their time, stopping to eat and drink on their way to the coast.

If it begins raining too late to make the spawning date, some crabs will stay in their burrows and migrate the following month instead.

And from BBC Earth, narrated by Attenborough. Note that the crabs breathe through gills, which must be kept moist. They live on land, but in moist habitats, but a remnant of their evolutionary origin is their need to go back to the ocean to spawn. Note that they walk sideways.

Note that they mate during the migration, too, so it’s not just females who are drawn to the sea at this time. A similar video, but also showing one of their predators and some of the other dangers they face.

I especially like this video because it shows how the island’s human inhabitants care for and protect the crabs:

Readers’ wildlife photos

March 28, 2024 • 8:15 am

Today we have some photos from the Galápagos by Ephraim Heller. His narration and IDs are indented, and you can enlarge the photos by clicking on them.

You have published lots of photos from the Galapagos Islands over the years. Here is my contribution to the genre. I took these photos on a March 2022 trip. They are divided into two classes first identified by Linnaeus: birds and non-birds. Each will be posted separately. First the non-birds.
Galapagos sea lions (Zalophus wollebaeki). Sea lions use whiskers for social communication (from Chilling Seals):
Sea lions, like other pinnipeds, have a highly developed sense of touch, which they utilize both in their aquatic and terrestrial environments. They possess long, sensitive whiskers known as vibrissae, which are dense clusters of sensory hair follicles. These vibrissae play a crucial role in the sea lion’s ability to navigate through their environment, locate and capture prey, and communicate with conspecifics.
Research suggests that sea lions do, in fact, use their vibrissae to recognize each other. These whiskers are rich in nerve endings, allowing them to perceive even subtle tactile cues. When sea lions come into close contact, they engage in a behavior known as ‘whisker touching,’ where they gently touch each other’s vibrissae. This behavior is considered a form of non-vocal communication and is thought to serve as a means of social bonding and identification.
Each sea lion’s whisker pattern is unique, similar to a human fingerprint, allowing for individual identification. Sea lions use their whiskers to recognize each other by comparing the unique pattern and structure of the vibrissae. This recognition process involves a combination of tactile exploration and visual inspection. Sea lions often nuzzle or touch each other’s whiskers to gather information about the individual they are interacting with.
Furthermore, sea lions possess a specialized neural network in their brain known as the somatosensory system, which processes information from their vibrissae. This system allows them to discriminate between different whisker patterns, aiding in the recognition and identification of conspecifics.

Sea lion pup being cute. They are experts at this:

Nursing sea lion pup:

Galápagos green turtle (Chelonia mydas). Per Wikipedia:
A subspecies of the green sea turtle. The species’ common name does not derive from any particular green external coloration of the turtle. Its name comes from the greenish color of the turtles’ fat, which is only found in a layer between their inner organs and their shell.
Since green sea turtles migrate long distances during breeding seasons, they have special adaptive systems in order to navigate. In the open ocean, the turtles navigate using wave directions, sun light, and temperatures. The sea turtles also contain an internal magnetic compass. They can detect magnetic information by using magnetic forces acting on the magnetic crystals in their brains. Through these crystals, they can sense the intensity of Earth’s magnetic field and are able to make their way back to their nesting grounds or preferred feeding grounds.

Galápagos giant tortoise (Chelonoidis niger). Per Wikipedia:
The species comprises 15 subspecies (13 extant and 2 extinct). It is the largest living species of tortoise, and can weigh up to 417 kg (919 lb). They are also the largest extant terrestrial cold-blooded animals (ectotherms). With lifespans in the wild of over 100 years, it is one of the longest-lived vertebrates. Captive Galapagos tortoises can live up to 177 years.
Galápagos tortoises are native to seven of the Galápagos Islands. Shell size and shape vary between subspecies and populations. On islands with humid highlands, the tortoises are larger, with domed shells and short necks; on islands with dry lowlands, the tortoises are smaller, with “saddleback” shells and long necks. Charles Darwin’s observations of these differences on the second voyage of the Beagle in 1835, contributed to the development of his theory of evolution.

Galapagos marine iguanas (Amblyrhynchus cristatus). Per Wikipedia:
Unique among modern lizards, it is a marine reptile that has the ability to forage in the sea for algae, which makes up almost all of its diet.
Researchers theorize that land iguanas (genus Conolophus) and marine iguanas evolved from a common ancestor since arriving on the islands from Central or South America, presumably by rafting. The land and marine iguanas of the Galápagos form a clade, the nearest relatives of which are the Ctenosaura iguanas of Mexico and Central America. Based on a study that relied on mtDNA, the marine iguana was estimated to have diverged from land iguanas some 8–10 million years ago, which is older than any of the extant Galápagos islands. It has therefore traditionally been thought that the ancestral species inhabited parts of the volcanic archipelago that are now submerged. However, a more recent study that included both mtDNA and nDNA indicates that the two split about 4.5 million years ago, which is near the age of the oldest extant Galápagos islands (Española and San Cristóbal).
The different marine iguana populations fall into three main clades: western islands, northeastern islands and southeastern islands. These can be further divided, each subclade generally matching marine iguanas from one or two primary island, except on San Cristóbal where there are two subclades (a northeastern and a southwestern). However, even the oldest divergence between marine iguana populations is quite recent; no more than 230,000 years and likely less than 50,000 years. On occasion one makes it to another island than its home island, resulting in hybridization between different marine iguana populations.

Galapagos land iguana (Conolophus subcristatus).
Charles Darwin personally disparaged these beauties as “ugly animals, of a yellowish orange beneath, and of a brownish-red colour above: from their low facial angle they have a singularly stupid appearance.” But what did he know, anyway?
Per Wikipedia:
Because fresh water is scarce on its island habitats, the Galápagos land iguana obtains the majority of its moisture from the prickly-pear cactus, which makes up 80% of its diet. All parts of the plant are consumed, including the fruit, flowers, pads, and even spines.
The Galápagos land iguana has a 60 to 69 year lifespan.

I’m pretty sure that Captain Kirk engaged in hand-to-hand combat with the Gorn subspecies:

Galapagos lava lizard (Microlophus albemarlens). Per Wikipedia:
There are seven species within the Galapagos lava lizard population and these species are found on several islands.
The major defense mechanism used by these lizards involves dropping their tail; their tail continues to move and thus distracts their predators while the actual lizard will camouflage or flee.

Painted ghost crab (Ocypode gaudichaudii). I love the eye stalks.

Sally Lightfoot crab (Grapsus grapsus). Quite beautiful, IMHO.

Terrestrial hermit crab (superfamily Paguroidea). This individual seems very pleased to have his photo taken.

Readers’ wildlife photos

January 1, 2024 • 8:15 am

I have but three batches of wildlife photos left, so we’ll run out on Thursday—and then I’ll have to stop this feature (the website is moribund anyway). Please send in your high-quality wildlife pictures if you have them.

Fortunately, Mark Sturtevant is here today with a good batch of insect photos (and one crustacean). His captions and IDs are indented, and you can enlarge his photos by clicking on them.

Over a year ago, the family traveled to New Jersey to visit family. I had already posted pictures from that trip some months ago, but I had lost track of another set. Here is that set.

We had not been to the area for about 8 years, and since then the invasive Spotted Lanternfly (Lycorma delicatula) had arrived. I expected that I would be photographing them, and I admit to some initial excitement about that since they are very large for planthoppers and are quite beautiful. There was certainly no problem locating some, since the buggers were just about everywhere! They decorated my brother-in-law’s house and most of the trees, and they often aggregated in solid patches in shady areas. Lanternflies were meanwhile also flying through the air like locusts. Here are adults and nymphs. Younger nymphs are black and white spotted, but this was late summer so I did not see those. Photographing them was slightly challenging since they are powerful jumpers, but with so many opportunities to get pictures it was still like shooting fish in a barrel.

Although the nymphs and the hind wings of the adults are quite colorful, I have not found anything about the colors being a warning that they are toxic.

As I said, I was at first looking forward to photographing these exotic insects, but it did not take me long to develop a strong dislike for Spotted Lanternflies! They were a constant presence when simply walking down a street or exploring a park. We even had to shoo them away when trying to enter a local restaurant, and taking care to not let any of the damn things fly inside

The Spotted Lanternfly is native to China, where it is under control by parasitic wasps. There seems no prospect of replicating that here, and I am not sure why. But such means of pest control do often fail because they are not cost effective, and similar approaches have resulted in unintended consequences. Spotted Lanternflies were first detected in the U.S. in 2014, and they have spread mainly because their egg masses can be accidentally transported on anything man-made. Now much of the eastern half of the country has them, and there are isolated populations out west as well. I understand that the main eastern population has now spread to my state of Michigan, and it’s probably only a matter of time before they turn up in my area, like the Spongy Moths (formerly Gypsy Moths), and Japanese Beetles before them.

These plant-sucking insects will feed on almost 200 plant species, and are considered a serious pest on grape vines. But many of our ornamental trees are fair game as well, and besides being obnoxious to humans, their large numbers are stressful for their host plants. But by far their preferred host is Tree of Heaven (Ailanthus), a rather attractive invasive tree that has become widespread in the U.S. for at least a century. So with a favored host plant already well established, there is little to slow further migration of the Spotted Lanternfly! The last picture is a typical scene on an Ailanthus sapling. But I have seen gatherings far denser than this.

Well, let’s move on. At a nearby park (also awash with Lanternflies), there were several of these Yellow-legged Mud Dauber Wasps (Sceliphron caementarium) collecting mud to build their nests. I had to hang head down on a steep river bank and hold the camera way out to get close pictures. When she completes her mud-pot nest, this wasp will stock it with paralyzed spiders for her young. [

On another outing near the ocean, I visited some tide pool areas where there were large numbers of these Atlantic Marsh Fiddler Crabs (Uca pugnax). They would all scatter to their burrows when I approached, so I had to wait in hiding. When some crept back into range, I was able to dive on this one for pictures. It’s the males that have the super-sized claw, which they wave at females to attract them. They will also use the claw to ritualistically arm wrestle other males.

 

In the same area there were numerous dragonflies, and on that one day I scored two new species from the Skimmer family. Here are Seaside Dragonlets (female and male, respectively) Erythrodiplax berenice.

And finally, a male Great Blue Skimmer (Libellula vibrans). This is one of our largest Skimmers, and I was very excited to get this picture!

ZeFrank has crabs!

October 30, 2023 • 1:30 pm

Reader Mary sent me a video by the incomparable ZeFrank, and it’s a lovely one, a full 15 minutes about crabs with lots of great video and accurate biology. Mary said this:

Really good one with lots of interesting evolutionary implications!

There’s all kind of cool stuff about coconut crabs, the famous migrating red crabs of Christmas Island, hermit crabs, sponge crabs, decorator crabs, boxer crabs (don’t miss these!), spider crabs, fiddler crabs  And yes, there’s evolution: straight adaptation in morphology and behavior by natural selection, sexual selection, and evolutionary tradeoffs.

(There’s an ad from 2:45 until 3:35.)

h/t: Tim

Mantis shrimp dismantles clam

July 28, 2023 • 2:00 pm

It’s Friday afternoon, the ducks are fed and watered for the weekend (it’s hot today but will cool down) and I’m soon off to hear about the fate of Botany Pond. This all means that it’s time for ani animal video.

How does it do this?  See the next video, which shows that the shrimp actually packs a double punch, with the second involving boiling water.

The explanation from Wikipedia:

Mantis shrimp are commonly separated into many (most fall into spears and smashers but there are some outliers)[9] distinct groups determined by the type of claws they possess:

  • Smashers possess a much more developed club and a more rudimentary spear (which is nevertheless quite sharp and still used in fights between their own kind); the club is used to bludgeon and smash their meals apart. The inner aspect of the terminal portion of the appendage can also possess a sharp edge, used to cut prey while the mantis shrimp swims.
  • Spearers are armed with spiny appendages – the spines having barbed tips – used to stab and snag prey.

Both types strike by rapidly unfolding and swinging their raptorial claws at the prey, and can inflict serious damage on victims significantly greater in size than themselves. In smashers, these two weapons are employed with blinding quickness, with an acceleration of 10,400 g (102,000 m/s2 or 335,000 ft/s2) and speeds of 23 m/s (83 km/h; 51 mph) from a standing start.[10] Because they strike so rapidly, they generate vapor-filled bubbles in the water between the appendage and the striking surface—known as cavitation bubbles.[10] The collapse of these cavitation bubbles produces measurable forces on their prey in addition to the instantaneous forces of 1,500 newtons that are caused by the impact of the appendage against the striking surface, which means that the prey is hit twice by a single strike; first by the claw and then by the collapsing cavitation bubbles that immediately follow.[11] Even if the initial strike misses the prey, the resulting shock wave can be enough to stun or kill.

Smashers use this ability to attack crabs, snails, rock oysters, and other molluscs, their blunt clubs enabling them to crack the shells of their prey into pieces. Spearers, however, prefer the meat of softer animals, such as fish, which their barbed claws can more easily slice and snag.

Readers’ wildlife photos

July 20, 2023 • 8:15 am

Today’s photos of Costa Rica come from reader Leo Glenn. His narrative is indented, and you can enlarge the photos by clicking on them:

Here are some photos from my recent trip to Costa Rica. We spent most of our time on the Pacific side in the northwest region, in Guanacaste Province. The Pacific side has more distinct dry and rainy seasons, in contrast with the Caribbean side, which receives considerably more rainfall year round. Although slightly smaller in land area than the U.S. state of West Virginia, Costa Rica boasts 32 national parks, over 50 wildlife refuges, and over a dozen forest and biological reserves. This creates tension, of course, between preservation efforts and ecotourism, which is the country’s largest source of income.

The view from a higher elevation, about 20 minutes from where we stayed.

The local beach, Playa Avellanas, was a short walk from our lodging via a boardwalk that traversed a mangrove swamp, comprised mostly of White Mangrove (Laguncularia racemosa). After an earthquake in 2012, the land along the coast rose one meter, which closed off the mouth of the river, causing the water in the mangrove swamp to stagnate and kill all of the trees (thus the many dead trees in the foreground). A restoration effort was undertaken to restore the area and replant the mangroves. It appears to have been largely successful, though it will be years before the new trees mature and the ecosystem returns to something close to its pre-earthquake state.

The shallow and drier areas of the swamp were populated by several crab species, including the Racer Mangrove Crab (Goniopsis pulchra).

 

The forested areas on the path to the beach were dotted with numerous small burrows,  inhabited by Red Land Crabs (Gecarcinus quadratus), which would freeze when approached, before slowly slinking backwards into their holes.

 A juvenile Atlantic Ghost Crab (Ocypode quadrata). They were lightning fast, and very hard to photograph.

Some Brown Pelicans (Pelecanus occidentalis), flying over the beach. There were quite a few more in the line. Apparently, a group of pelicans can be called a pod, a pouch, a scoop, a squadron, or, if fishing as a group, a fleet.

Although colorful butterflies were abundant, I lacked the skill, patience, and hardware to photograph them, unless, as in this instance, I got lucky when one happened to land in the swimming pool. We rescued it immediately, of course, and after a few minutes spent drying its wings, it took flight. Theona Checkerspot (Chlosyne theona).

I did manage one halfway decent photo of an Apricot Sulphur (Phoebis argante).

A Crested Caracara (Caracara plancus), described on Wikipedia as “a bold, opportunistic raptor, often seen walking around on the ground looking for food,” which is exactly what this one was doing.

A nest of Northern Warrior Wasps (Synoeca septentrionalis), in a tree outside our lodging. According to Wikipedia, “It is a swarm-founding wasp that is also eusocial, exhibiting complicated nest structure and defense mechanisms.” The nest was about 30 ft up in the tree, and without a telephoto lens (or a very long stepladder), this was the best photo I could get. Its high location in the tree was a comfort to us, being so close to our rental house. Though not a particularly aggressive species, they are reported to have a very painful sting.

Readers’ wildlife photos

July 17, 2023 • 8:15 am

Today’s photos come from evolutionist Jody Hey from Temple University. His narrative and captions are indented, and you can click on the photos to enlarge them.

The coast of Maine offers a lot of beautiful scenery and some great wildlife watching. My visits there are usually in mid-summer,  which if you are inland is not the best time of year for watching birds. However,  the seaside has lots of visible action year round.  On or near the coast, many of the birds are large, and the sightlines have few obstructions, so getting passable photographs can be relatively easy.  Below are some pictures taken at Marshall Point, the location of a much photographed lighthouse near Port Clyde, and the island of Monhegan,  home to a small community of lobstering folk and artists, and just a  12 mile ferry ride from Port Clyde.

Marshall Pt is a public park and makes a popular and idyllic picnic  spot when the weather is good.    This photo shows the Marshall Pt lighthouse at high tide.  Many will recognize it, as it was famously the eastern terminus for one of Forest Gump’s cross-country runs.

One day I had just finished my picnic lunch and was walking on the beach facing the harbor of Port Clyde, and saw this Great Black-backed gull (Larus marinus) enjoying its own lunch, an Atlantic rock crab (Cancer irroratus).

The tidal range is quite large in coastal Maine, especially further north and east, so the things to see vary widely throughout the day.  Here is a Least sandpiper (Calidris minutilla) exploring the barnacles at low tide.

Marshall point is separated from ocean waters only by a few islands, unlike much of the jagged cost of Maine most of which is some distance from the open ocean.  This means that Common Eiders (Somateria mollissima) can be seen there year round.   In the summer their markings are fairly dull,  but in the winter and spring,  they are spectacular.

The ferry ride from Port Clyde to Monhegan offers some great opportunities to see marine mammals,  including a couple varieties of seals and Harbor Porpoises (Phocoena phocoena):

Monhegan island itself is less than 5 square miles in area,  however the majority of it is owned and maintained as wild land by a private non-profit land trust.  Visitors are free to explore the beautiful woods and rocky cliffs that dominate the eastern side of the island, as well as eat and shop in the little village.  The cliffs also offer great viewing of a variety of coastal and ocean-going birdlife.

Northern Gannets can often be seen from the cliffs  (as well as from the ferry).  Here is a somewhat blurry adult,  and a more in-focus juvenile:

This Double-crested Cormorant (Nannopterum auritus) obligingly flew directly below me at the same time as the waves were crashing:

The cliffs are also a popular nesting site for Herring Gulls (Larus argentatus):

These Cedar waxwings (Bombycilla cedrorum) were also at the Monhegan clifftops one day,  though the coastal location was fortuitous as they are a widespread and common species:

And closely things out for Monhegan,  I go this lucky shot of a Common Raven (Corvus corax) one day, deep in the spruce woods:

Lastly,  a lagniappe  (as Jerry would say).  Not far from Monhegan and Marshall Point is Eastern Egg Rock,  home to the world’s first restored colony of Atlantic Puffins (Fratercula arctica).  The story of that restoration is fascinating,  and now it is apparently safe for the birds to be seen by tourists during the breeding season (from a boat, that is).  I took the boat tour one day a couple years ago,  just before the end of the season when there were only a few puffins to be seen,  but at least I got a picture: