A Little Bit More
The process of shedding the exoskeleton or skin is called ecdysis. Such periodic molts are essential for growth to occur in some animals, but the intervals between molts vary with a wide range of environmental factors. The process of molting is usually simply stated in the literature, but is actually a complex and perilous procedure for crayfish.
Ecdysis in crayfish is completed in 4 basic stages:
- The process begins when a crayfish lays down a new, soft exoskeleton under the old one, the same in every detail as the old, including the pigment. The animal then withdraws certain mineral salts from the old shell and stores them in its tissues.
- At this point, the old shell is simply a tough cuticle. Key suture areas soften, permitting the shell to split and the claws and body to be withdrawn.
- The crayfish now absorbs water from its surroundings, expanding its new, still soft exoskeleton to a size larger than the original one. Out of the old shell, the crayfish is limp and almost unable to move. In preparation for this, the crayfish had sought out a safe, secluded location before beginning ecdysis.
- The mineral salts that were extracted from the old shell are now deposited in the new cuticle. After several days, the shell is sufficiently hard for the crayfish to venture out of hiding and resume its normal activities with renewed vigor.
Research on crayfish ecdysis has shown that the process is a dangerous one, even if predators are discounted; many crayfish die before they finish the molting process.
Crayfish, also known as crawfish, crawdads, or crabs, are found in a variety of aquatic or at least moist habitats across North America. They are omnivores, feeding mainly on plant material but scavenging animals material as well. The crayfish's most obvious characteristic, its strong claws, are used for crushing, picking up, and tearing food, as well as defense. Anyone pinched by even a medium-sized crayfish can attest to its strength!
Adult crayfish are basically nocturnal, but the young are active during the day. Crayfish are usually found in permanent bodies of water, although some species are found in areas where standing water is only temporary. Several species habitually burrow in the soil and their mud-ringed holes are often mistaken for "snake holes". These burrows vary in size, shape, and depth, but all must reach groundwater, for each inhabitant must have water to keep its gills wet.
Activities
Darkling Beetle observations
Objectives: See ecdysis as part of the growth cycle of a common beetle
Materials: container with mealworms
Many different animals go through the process of ecdysis - it's easier to observe than you may think. Mealworms (not worms at all, but immature Darkling Beetles) shed their skins as they grow and are easy to raise and observe. A mealworm colony is easy, inexpensive, and interesting to establish.
Pet stores have large supplies of inexpensive mealworms that they use as pet food. You can easily start a colony for less than one dollar. Tell your local pet store that you want to start a small mealworm colony and ask them to tell you how to house and feed these insects. Tell them you're interested in seeing how they grow and change over time and would like to begin with the smallest (youngest) ones available (they will vary in size).
As the mealworms grow, they will shed their skins and you can gently remove these skins from the container and tape or glue them to a piece of paper. Over time you'll notice a size difference in the skins as the animals grow larger and larger. Be sure to look closely at the skins to see if you can tell where the skin breaks open and the mealworm crawls out. Your mealworm begins as a small larva (grub), grows larger and larger, then changes into a pupa, and then changes into the adult stage (Darkling Beetle).
Key Concepts
Structures and Functions, Growth and Development
Questions
Do you have a question for a naturalist? Go ahead and ask!
It's easy -- just fill out this form, submit your question and you'll receive an answer shortly.
Posted by Buzz Morrison on October 31, 2005 at 09:50 AM
Q: Can you tell me what genus/species of Crawdads we have along the front range around the Denver Colorado area
A: I don't know myself but I did find a great website that I hope will give you exactly what you want. Take a look at iz.carnegiemnh.org
Thanks for asking.
Posted by Margaret Blue on August 09, 2005 at 06:27 PM
Q: Crayfish have been introduced and are spreading quickly in my home town(Edmonton, Alberta). How will this affect our native species
A: I'm not sure what species of crayfish has been introduced into Edmonton, but the Rusty Crayfish is a real problem for many areas as the "Draw Your Weapons" unit points out. Take a look at this unit (www.enaturalist.org see if it answers your question.
One of the biggest problems with introducing non-native species into any area is that one can't be sure how it will affect the natural balance. Animals and plants that are a real asset in one area can become a real hazard in a different environment but we often don't know this until it's too late. There have been introductions of animals and plants into many areas of the world that have worked out really well so your crayfish introduction may or may not work out - only time will tell. Thanks for your question.
Posted by mary on April 26, 2005 at 09:21 PM
Q: My son recently brought a crayfish home from school after studying them in 4th grade. We bought 2 more from a pet store and today, a week later, we found 2 of them had died. We bought them fresh elodea but had not given them any protein. We bought cat food today to feed them, but too late.
Should we try to keep crayfish in a tank? What did we do wrong?
Thanks for your consideration in answering our questions.
MK, Harry and Jack
A: I think it's a great idea to have crayfish in an aquarium - they're interesting animals that we rarely get to observe closely. There are all kinds of possibilities as to why two of your crayfish died. You didn't say if the two that died were the two new ones or not. I could easily believe that the crayfish you bought in the store were not the same as the one your son had in school.
Crayfish vary with their needs as there are many different kinds of crayfish. So it is important that you know what kind you have and what its basic needs are. Usually the crayfish in pet stores come from exotic places so you'll need to find out where they normally live and then use that to figure out what conditions are best for them. Some will need cooler conditions than others and most, if not all, will need lots of oxygen in their water. If your aquarium was smallish and you added two more animals to the tank, maybe the oxygen level was simply too low. OR, some crayfish are much more aggressive than others and maybe your resident crayfish actually injured your others - I really can't say.
I wouldn't feed catfood to your crayfish as I envision it dissolving in the water and causing all kinds of a mess. Ask your pet store what they recommend. I like the Elodea (crayfish eat lots of plants) and I have also fed my crayfish goldfish pellets as these sink and have a nice mix of plant and animal products. Good luck to you and I hope you can continue to enjoy your crayfish.