All arthropods need to molt. Here is a time lapse video of how a spider crab does it.
When a crab is ready to molt it rapidly takes up water, causing pressure to build in its body cavities. The rigid outer exoskeleton breaks open and the crab is able to push itself out from inside its molt. The new exoskeleton is softer, so it is undamaged by the increase in body volume, but it will eventually harden over time. Recently molted, soft-shell blue crabs are commonly steamed and eaten whole in my neck of the woods.
Disney Nature has a new IMAX documentary out titled, ‘Oceans‘. A quick survey of the reviews of the film indicates that a mantis shrimp, Odontodactylus scyllarus, is a part of the most memorable sequence of the film. Here is a clip of the mantis shrimp’s scene, (available in 1080p on Youtube). Near the beginning there is a really nice shot of the pseudopupil (the facets of the eye looking directly at the observer).
I, however, have a couple criticisms of this sequence. First off, this was almost definitely shot in an aquarium. Secondly, what is it with IMAX movie makers and repeatedly pushing animals towards stomatopod burrows until they lash out? Similarly to the sequence from ‘Deep Sea 3D’ where an octopus is forced to approach the burrow of a Hemisquilla californiensis, the mantis shrimp in this video shows no interest in predating the crab. He just seems to be trying to get the crab away from his hole. Normally, the crab would surely oblige if it wasn’t for the Disney filmmakers repeatedly pushing it back.
I can’t help but be reminded of Disney’s ‘White Wilderness‘ documentary where the filmmakers pushed lemmings off a cliff into the ocean in order to convince people, incorrectly, that lemmings engaged in suicidal behavior. They are quite a viscous bunch over in the Magic Kingdom.
Spiny lobsters, Panulirus argus, have an unusual and poorly understood migratory behavior. Every autumn, many of the shallow living lobsters around the Bahamas begin forming traveling queues that aggregate into long chains of marching lobsters. These chains can swell to thousands of individuals as the animals migrate to deeper waters.
Our main man, David Attenborough, breaks it down and somehow manages to make a skittering train of lobsters feel epic:
As mentioned in the video, the migration possibly occurs in order for the lobsters to escape turbulence and turbidity in the shallows resulting from autumn storms that sweep into the Bahamas. The migration has long been observed in tight correlation with these storms. Following the first storm of the year, the spiny lobsters begin amassing at buildup areas and prior to embarking on the mass migration. The cue to begin queueing (hah) is likely the sharp water temperature drop following the first storm. Indeed, in laboratory observations, decreases in water temperature increased queueing among captive spiny lobsters.
The purpose of the lobster queue formation during migration is likely twofold. For one, traveling in a line reduces water drag for the lobsters traveling behind others. To borrow a term from racing, the lobsters are drafting on the wakes of their line-mates. In this manner, the lobsters conserver energy and momentum on their trek. The other reason for forming the migration queues is likely predator defense. Beyond projecting increased size via aggregation, the lobster queues can rearrange into a defensive circle to cover their vulnerable back-sides. You can see an example of the onset of defensive formations in the photo below.
Panulirus argus migratory train. The lobsters at the front of this train were perturbed by the divers, causing them loop back into the train, creating a lobster vortex. Adapted from Kanciruk and Herrnking, 1978.
- Kanciruk, P and Herrnkind, W. 1978. Mass migration of spiny lobster, Panulirus argus (Crustacea: Palinuridae): Behavior and environmental correlates. Bulletin of Marine Science, 28(4): 601-623,
How does a swarm of army ants take down a heavily armored fresh water crab? Let’s find out…
That’s gotta be a pretty terrible way to go.
Red in mandible and pincer…
Published March 8, 2010
Coleopterans (Beetles) , Decapods (Crabs, Lobsters) , Dipterans (Flies)
Tags: Aedes, Anopheles, Blue Crab, Callinectes, Disease, Dung Beetle, Invasion, Mosquitoes, Onthophagus, Stenocarid, Synthetics
Brief blurbs about recent arthropod news and research:
- The blue crab, Callinectes sapidus, has been found in England for the second time ever. These ill-tempered, but delicious, swimming crabs are native to North America; where they represent a major marine fishery despite serious conservation concerns. Previously, blue crabs have turned up in Japan and the Mediterranean. It is conventionally thought that these crabs were brought in as larvae in ship ballast water and have since gained a foothold in their new homes. It is possible that this blue crab in Cornwall also came over from America in ballast water, or it could have been carried on ocean currents up from the Mediterranean population. It is unclear weather this is an isolated individual or a representative of a new invasive population.
- You will be disappointed to learn that the horny females I referred to in the title are dung beetles. One usually associates the growth of horns and antlers with males who use them to battle for dominance in a social hierarchy or for their pick of the choicest females. However, female dung beetles, Onthophagus sagittarius, are known to have much more impressive horns than their male counterparts. A new study suggests that these horns are used by the females to compete over reproductive resources (i.e. poop). Size matched females with larger horns were found to achieve greater reproductive fitness, making horn size a positively selected female secondary sex characteristic in these beetles. (Via 80Beats)
Horned Onthophagus sagittarius females square off. Photo: Sean Stankowski
- New research reports the development of synthetic superhydrophobic materials inspired by tiny, water repellent hairs in insects. These hairs are found on the legs of water walkers and the backs of Stenocarid beetles, which use the hairs to channel water droplets to their mouth.
- The genomes of the malaria mosquito, Anopheles gambiae, and the yellow fever mosquito, Aedes aegypti, were published in 2002 and 2006, respectively. These sequencing efforts appear to be bearing a lot of fruit as of late; as several genetic approaches to controlling the spread of mosquito vectored diseases have been proposed. These include; increasing the immunity of mosquitoes to the dengue fever virus, weakening mosquitoes by preventing waste secretion, and preventing female mosquitoes from developing functioning flight structures. Some of these ideas are pretty far from real-world application unfortunately, and the buzz surrounding them seems to be the result of overly-excitable university PR departments.
The BBC has an audio slideshow of some plankton micro-photography. Plankton is not a taxonomic classification, but rather a bulk term for any pelagic aquatic organism that is typically not capable of out-swimming its currents. (I was recently in a prolonged argument with the owner of salt water aquarium store about this. I could not convince the person that a plankton was not a single type of organism.) Damn near every phylum I can think of has some planktonic species or life stages. You can be plankton if you can’t out-swim the current you are in.
In the BBC video you can see several planktonic crustaceans including adult copepods and euphausiids, as well as the larval stages of crabs. A neat feature to notice in the crab larvae are the long spines protruding from their backs. This is an anti-predation adaptation seen in many crustaceans, making the larvae more difficult to swallow. There is a great diversity of spine length and configuration in different species of larval crustaceans.
Some spiny larval crustaceans.
Photos: Peter Parks, Steven G. Morgan, Rudolph Scheltema, artour_a, Kim Taylor and Jane Burton.