By playing a simple card game based on the stages of metamorphosis, students will:
- Learn how insects change in form as they grow.
- Consider the advantages of undergoing this metamorphosis.
© John Wright
Ever played the card game Go Fish? If you know the rules, you can easily learn how insects undergo the stages of metamorphosis to become an adult.
By playing a simple card game based on the stages of metamorphosis, students will:
Explain rules of Go Bug! (5 min.) Explain how to play Go Bug! following the rules described below. This activity is a variation on the common card game entitled “Go Fish!”
Oversee game play (30 min): Assist and direct groups with game play as needed. All groups should play one complete round. Have students play as many games as they have time for. Consider mixing up the groups if possible.
On a white-board, or similar display, make a table to compare insects undergoing complete and incomplete metamorphosis. Call on students to tell you which insects fall into either category.
Ask the following questions:
adult: the final, breeding stage of an insect’s life cycle, typically involving the growth of wings.
bug: true bugs are an order of insects called Hemitera, which includes 50,000 – 80,000 species and is comprised of cicadas, aphids, leafhoppers, “stink bugs,” water striders and others.
egg: the unborn stage of an insect.
host: the organism inside which a parasite grows and feeds.
larva (plural: larvae, pronounced LAHR-vee): the immature stage of an insect with complete metamorphosis, primarily involving voracious feeding and rapid growth. Larvae look very different from the adult insects they will become.
metamorphosis: the change of an insect (or other animal) from one form into another as it progresses to adulthood.
molt: the shedding of an insect’s outer skeleton as it grows too large for it.
nymph [nimf]: the immature stage of an insect with incomplete metamorphosis, primarily involving voracious feeding and rapid growth. Nymphs resemble the adult insects they will become through a process of growth and molting.
parasite: an organism that lives in (or on) a host organism and obtains nourishment from the host without benefiting or killing it.
pupa: the inactive stage between larva and adult, when no feeding occurs.
Insect Life Cycles
In biology, a life cycle refers to the period between an organism’s birth and its death, typically including reproduction. For many animals, including humans, a life cycle consists of the physical growth and maturation of a single body form. In other words, a baby is essentially a miniature version of an adult. When we compare this type of development with that of insects, or say, frogs, we note these later organisms progress through multiple body forms instead of a single form. Think of a butterfly. Emerging from an egg, is a caterpillar. That caterpillar grows and grows until one day it forms a cocoon around itself. Weeks later, a butterfly emerges from the cocoon bearing very little resemblance to the creature that created it. And yet, these two remarkably different forms are the very same animal.
This transformation from one form into another is called metamorphosis. There are three basic kinds of metamorphosis in insects. Some types of insects undergo a three-phase life cycle (egg-nymph-adult) called incomplete metamorphosis. Other insects have a four-phase cycle (egg-larva-pupa-adult) called complete metamorphosis. Some insects go through no metamorphosis at all, but this type of development is very rare and won’t be discussed in this activity. Essentially, these “ametabolous” insects hatch from their eggs looking like tiny versions of adults.
Metamorphosis in Other Animals
Insects aren’t the only animals that undergo metamorphosis. Most students are familiar with the development of frogs (egg-tadpole-pollywog-adult), but countless lesser-known examples of metamorphosis may be found in marine invertebrates including mollusks, crustaceans, cnidarians, echinoderms and tunicates. Even fish such as salmon, flounder and lampreys undergo a form of metamorphosis. In all these cases, changes in body forms typically coincide with a change in habitat and behavior.
Incomplete metamorphosis is a term used to describe the mode of development of insects that pass through three distinct stages: the egg, the nymph, and the adult stage, or imago. Only 10 - 15% of the insects on Earth undergo incomplete metamorphosis. These insects go through gradual changes in size without a pupal stage (see Complete Metamorphosis).
These insects start as eggs, which are sometimes so small you cannot see them. When the egg hatches, a nymph comes out. Most of the time, the nymph looks similar to the adult, but smaller, with different coloration, and lacking wings and sexual organs. The nymph grows through stages called instars, shedding its 'skin' at each stage. Finally, it changes into an imago, the sexually mature adult with wings.
Aquatic insect nymphs, such as the mayfly illustrated above, usually have gills and look very different from the adults they will turn into.
Insect Orders with Incomplete Metamorphosis:
Complete metamorphosis is a term used to describe the mode of development of insects that pass through four distinct stages: the egg, the larva, the pupa and the adult stage, or imago.
These insects also start as eggs. When the egg hatches, a larva comes out. The larva often resembles a worm and will feed voraciously so that it can quickly grow bigger. When the larva has reached its maximum size, it changes into a pupa. The pupa usually cannot move or eat. During the pupal stage, the larva changes into an adult that will look very different from the larva, typically inside a protective casing, such as a chrysalis, as in butterflies and moths. While inside the pupa, the insect will excrete digestive juices to destroy much of the larva's body, leaving a few cells intact. The remaining cells will begin the growth of the adult, using the nutrients from the broken down larva. The final, adult stage includes a fully developed insect with wings and reproductive organs.
Insect Orders with Complete Metamorphosis:
Advantages of Complete Metamorphosis
There are an unbelievable number of insects out there. They occupy every niche on land known to man. This means that competition between and within species is often very high. Thus, the greater the difference in habits and habitats a species utilizes, the greater its advantage for survival and reproduction. For this reason, insects with complete metamorphosis, i.e. two radically different, active forms – larva and adult, have an advantage over insects with incomplete metamorphosis.
With complete metamorphosis, there is a tidy division of labor. The primary job of the larvae is to eat and grow. Adults on the other hand, are responsible for mating and the production of offspring.
Consider, if the adults of a certain species of insect fed on the same food as their larval forms, the larvae may deplete that food source before the adults have a chance to feed. So diversification of feeding habits can be a huge benefit to animals like insects whose food sources might be seasonally fleeting or simply scarce.
Diversification of physiology can also pose an advantage when it comes to predation. For example, if most of the winged adult mosquitoes get eaten up by a swarm of dragonflies, the aquatic mosquito larvae remain unharmed, safe at least from dragonfly adults.
Nearly all insects are attacked by one or more insect parasites. These parasites are predominantly solitary wasps and a group of flies called Tachinids. These insects lay their eggs inside the bodies of an insect host. When the egg hatches, the larvae feeds on the host from the inside out! The larvae may continue to grow and even metamorphose within the host. In the end, the parasite kills the host before crawling out of it to go mate with other members of its species.
While some parasites target adult insects, others seek the eggs, larvae or pupae of host species. Often, parasites have very specific hosts. One species of parasitic wasp may have a single host species. Insect parasites can be very beneficial in the control of agricultural pest insects.
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