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From Roly Polies to Praying Mantises

And Beyond!


We’ve all seen ant farms, or kits for growing your own Sea Monkeys, and we explored these fun, educational, temporary pets last time on “Biology Bytes.” But these days there are a lot of other live organisms that kids of all ages can easily obtain, watch grow, and use as a stimulating introduction to (or fun refresher in) the field of biology.

Not only is the market today full of little critters and complete rearing kits that can be purchased for educational purposes, there are also many tools that biology enthusiasts of all ages can use to explore and appreciate the life that is all around them. Due to their small size and short lifespan, these organisms can also make a perfect temporary “pets.”

The stealthy, cannibalistic praying mantises (which belong to the family Mantidae) are probably one of the most captivating and respected insects, and have intrigued people around the world for centuries.
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The stealthy, cannibalistic praying mantises (which belong to the family Mantidae) are probably one of the most captivating and respected insects, and have intrigued people around the world for centuries.

Praying Mantises Probably one of the most captivating and respected insects is the praying mantis, a stealthy cannibalistic predator. Over 2,000 species of praying mantises live around the world, mostly in warm, subtropical, and tropical areas. Their elongated bodies vary greatly in length, from the South American neotropical Mantoida tenuis, which barely reaches half an inch, to the African Ischnomantis gigas, which can be over six and a half inches long.

People around the world have been intrigued by these creatures for centuries. Mantises observed by people in Asia millennia ago were recognized as the strong, bold predators that they are. In the 900s AD, capturing and breeding mantises for fighting was a widespread practice. On the other hand, it took Europeans a while to recognize the true nature of mantises. They were thought be a type of vegetarian grasshopper, and to have mystical insight and be pious in demeanor, because of their calm manner and their forelegs held up in a praying-like fashion (this is how they got their common name as well as their scientific one in Europe, Mantis religiosa). But by the mid 1700s this image was beginning to fade. European entomologists noticed that praying mantises battled each other fiercely, with the winner frequently eating its fallen opponent.

After this epiphany, it started to be widely recognized that praying mantises embody many characteristics that make them ideal little hunters. They come in a range of greens, yellows, and browns, colored to blend in with their environment. While invisibly and patiently waiting to ambush their prey, they can easily take in their surroundings, with some able to turn their heads an amazing 300 degrees while their bodies remain still. Mantises also have wings that they use to assist with leaping, though it’s usually so quick that people can’t even see the wings being used. Mantises can fly, too. The “praying” forelegs, this hunter’s most famous characteristic, are used to quickly grab and securely hold prey in place while devouring it. Mantises are opportunistic hunters: They’ll catch and eat just about anything they can, from flies and other small insects to prey their own size or even bigger, up to small vertebrates such as frogs, mice, lizards, and more.

And yes, praying mantises infamously will eat their own kind, even while mating, an act known as “sexual cannibalism.” The female mantis is usually much larger than the male, often about twice his size, and consequently it can be very dangerous for him to approach a female. The female can strike and capture the male as he approaches her, or after he has dismounted her. But perhaps most amazing is that she can also reach around with a foreleg and grab his head or upper body while he is on her back, copulating with her, and proceed to eat him alive. Because of the male’s anatomy, he can continue copulating while he’s being eaten. There’s a lot of heated debate over why mantises do this; one thought is that eating their mate helps females have more energy for the taxing process of creating eggs, which could benefit the survival of the species as a whole.

Like any living animal, praying mantises should be treated with respect, especially because they can mistake wiggling digits for prey, and, despite being fierce fighters, they’re very delicately built. To watch these amazing predators in action, you can set up your own habitat with plenty of food (flightless fruit flies are great for this, and can be purchased at most local pet stores). Mantises in captivity live about six months to a year, and egg cases or adults can be purchased from many places online, including Insect Lore, the Connecticut Valley Biological Supply Company, or theCarolina Biological Supply Company.

Centipedes and Millipedes While it may not always be easy to find praying mantises in your back yard, there are many other little critters that can usually be discovered if you’re looking in the right places. Centipedes and millipedes easily fall into this category. They’re arthropods, which means they’re invertebrates with an exoskeleton, a segmented body, and jointed appendages—like insects, spiders, crustaceans, and others in this group.

Centipedes and millipedes can look similar at a glance. Both have long, narrow bodies with segmented sections, are similar in length, and thrive in similar habitats. There are over 8,000 millipede species, ranging in size from less than one tenth of an inch long, to a few giants over 12 inches in length. Similarly, the largest of the 2,800 species of centipedes can reach 10 inches long. They prefer similar habitats; they can be found under pieces of loose, decaying bark, or under rotting logs, or in damp soil under rocks.

But upon closer inspection, one can easily see that these arthropods are very different in many ways that pertain to their diets and how they should be handled. Although the millipede’s name means “a thousand legs,” even the biggest ones never have over 300 legs, and while some centipedes can also have well over 200 legs, most have far fewer. While a millipede has a very rounded body, resembling a worm, a centipede has a much flatter body, usually with longer legs sticking out on the sides, in particular the first pair of legs, which have been modified to act as poisonous fangs! This lets the centipedes catch prey and fight off predators. Some of the larger centipedes can even capture small vertebrates, like little lizards and mice, although most centipedes eat much smaller, slower animals, such as worms, small insects, and weaker centipedes.

Millipedes, in marked contrast, only eat plant matter, such as decaying leaves, carrying out an important role in the composting process. And while millipedes don’t have poisonous fangs with which to protect themselves, most do have very powerful stink glands to discourage predators. The noxious hydrogen cyanide gas released by some millipedes can even kill small insects.

Millipedes and even whole millipede kits can be purchased from Insect Lore, the Connecticut Valley Biological Supply Company, or the Carolina Biological Supply Company, which also sells centipedes. It’s simple to set up your own millipede habitat too. Always handle with care these potentially noxious and poisonous creatures!

Pill Bugs and Sow Bugs While millipedes and centipedes can often be found under damp, rotting wood, there are other tiny animals that are even easier to find in these places, such as pill bugs and sow bugs — you’d be hard pressed to find a yard in California that these industrious little bugs aren’t living in. Like millipedes, these critters eat decaying plant matter, but they take it a step beyond: They’re omnivorous and will eat other decaying material as well, including dead animals and even their own feces. Consequently, they serve a very important role in compost heaps and recycling nutrients in the soil in general.

They may not look like it, but pill bugs and sow bugs are actually crustaceans, like crabs, lobsters, and shrimp. (This means they’re also arthropods, like millipedes, centipedes, and insects, as crustaceans belong to the larger arthropod group.) And they’re particularly successful crustaceans; theirs is the only crustacean group that has members dwelling in the entire range of terrestrial habitats, with some 4,000 species living everywhere from seashores to deserts.

How have these amazing crustaceans evolved to conquer the land? Because pill bugs and sow bugs probably evolved from a marine ancestor, their biggest challenge in colonizing land has been water retention. Selecting moist habitats, such as under damp rotting logs and in damp soil, helps them retain their water. They’ve also evolved some interesting anatomical features. They conserve their own water content within themselves by recycling their own digestive fluids and urine, and can quickly uptake standing water and can even absorb water from vapor.

The most common and extensively studied member of this group is the three-quarters-of-an-inch long Armadillidium vulgare, so named because of its ability to roll into a ball like an armadillo to defend itself. It’s also known as the common pill bug or roly poly. (Sow bugs, which belong to the genus Oniscus, can’t roll up.) A. vulgare long ago lived only in southern Europe, but human colonization spread it across Europe and brought it to North America. There actually aren’t any pill bug species native to the U.S., so A. vulgare has flourished without native competitors, and is particularly abundant in coastal California.

Sow bugs and roly polies make great short-lived pets (living up to around three years). They can often be found in great numbers on damp soil under rocks or decaying wood. Alternatively, they can be purchased online at Insect Lore, the Connecticut Valley Biological Supply Company, or the Carolina Biological Supply Company.

Other Educational Critters Many of the following animals or plants can be purchased online at Insect Lore, the Connecticut Valley Biological Supply Company, the Carolina Biological Supply Company, or through other online vendors.

Earthworms Like millipedes, sow bugs, and pill bugs, earthworms are also extremely important in recycling nutrients in soil. They eat mostly decaying plant and animal matter and their thoroughly processed excrement, called casts, redistributes these nutrients to different layers of the soil. One of the largest earthworm species is Australia’s giant Gippsland earthworm (Megascolides australis), which can, astonishingly, be over 10 feet long, weighing more than a pound. A variety of worm composters can be purchased online.

Caterpillars There are a number of different types of caterpillars that can be easily obtained and are fascinating to watch as they mature into butterflies or moths. Silk worms have been reared for millennia to make silk. Consequently, the eggs of these easy-to-care-for caterpillars can be purchased at many places online. Painted-lady caterpillars are also commonly used in classrooms. Alternatively, raising monarch butterfly caterpillars can be not only a great educational experience, but releasing the butterflies can also help restore their declining numbers in native areas.

Frogs and Tadpoles Although watching tadpoles mature into frogs is a great way to study the development process, it’s always important not to release an animal into an area it is not normally found in. For example, the human-aided spread of the American bullfrog and African clawed frog may also have helped spread a fungal disease that’s threatening amphibians with extinction.

Lastly, but perhaps most importantly, all sorts of tools can be used to further one’s backyard biology adventures, from bug-catching kits to critter cages, butterfly nets, magnifying glasses, microscopes, and much more. Many of these items, and more, are sold at local pet stores, but they can also be purchased online from stores such as Insect Lore, the National Science Teachers Association, and The Science Fair.

For more details on these little educational critters, see Frederick R. Prete, Harrington Wells, Patrick H. Wells, and Lawrence E. Hurd’s book The Praying Mantids, Ken Preston-Mafham’s book Discovering Centipedes & Millipedes, M. A. Alikhan’s book Terrestrial Isopod Biology (on pill bugs and sow bugs), K. E. Lee’s book Earthworms: Their Ecology and Relationships with Soils and Land Use, or Wikipedia’s articles on the Mantis, Millipede, Centipede, Isopoda (pill bugs and sow bugs), or Pill bug, or Insecta Inspecta World’s article on Praying Mantis, the University of Arizona’s Web site on Isopod, Pillbug, Sow Bug Information, the University of Kentucky’s website on Sowbugs and Pillbugs, or the Web site petbugs.com.

Biology Bytes author Teisha Rowland is a science writer, blogger at All Things Stem Cell, and graduate student in molecular, cellular, and developmental biology at UCSB, where she studies stem cells. Send any ideas for future columns to her at science@independent.com.

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