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Introduction
To understand why pests enter our homes, it is important to understand the concept of habitat. All living things require a suitable habitat in order to survive. A habitat
must provide four things — food, water, shelter (a place to hide, build a nest or lay eggs), and space (territory — to avoid competition). Each animal species is
unique in the kind of food it eats, how it gets water, where it hides and reproduces, and how much space it needs apart from others of its kind. Therefore, different animal
species require different habitats. And furthermore, any given plot of land can contain a variety of habitats and support a variety of species.
Pests that enter our homes are simply in search of suitable habitat.
Complete the activity entitled, "Could Your Dream House be a Mouse House?" Then look at the habitats of other pest species. Have students read the short background
information about the Indian meal moth. Discuss with students whether this species would be able to survive in the wild today without the presence of humans. It is likely
that prior to exploiting human stockpiles of grain, the ecology of this species was quite different. It would have been difficult for an adult moth to find a naturally
occurring stockpile of grain in which to lay its eggs' Discuss the terms adaptation and evolution. Use the story of the Indian meal moth as an example of a species that
became successful because it was able to adapt and evolve over time. Using the background readings provided as well as library and electronic resources, assign each student
or small group of students one pest species to research. Have them create a report with the following information, and share what they've learned with the class.
- Identify their pest's habitat today, using the four habitat requirements described above
- Describe how their pest's habitat may have changed over time and/or with the presence of humans. Is its habitat in the "wild" different from its habitat
when there are humans structures nearby?
- Speculate whether their pest could survive today without the presence of humans.
Activity — Could Your Dream House be a Mouse House?
Everyone daydreams from time to time about their dream house. Discuss the concept of habitat with students and have them each describe their ideal dream house, noting how the
four habitat requirements would be met. What kind of food would they need and how and where would it be stored? Where would their water come from? (If necessary, discuss
plumbing systems, pipes and wells.) Then read the following story of a house mouse describing its habitat:
My favorite thing to eat is seeds that come from grasses. When the wind blows in the fields where the grasses grow, the ripe seeds are scattered all around. I spend lots of
time searching for and gathering these seeds, and every so often, I stop to nibble. However, if there aren't any seeds around, I'll eat just about anything! I usually don't
need much water; I get enough from what's trapped inside the food I eat. I can have babies at any time of the year, as long as I can find a place that's warm enough. I like
warm protected places; they are good for building nests. I don't like being out in the open, though, especially during the day — too dangerous! I travel in tunnels of earth,
grass, wood, rocks, or whatever I can find. I don't mind living with friends or relatives but when it gets too crowded, we fight over the food, so I go in search of someplace
else to live. This happens a lot, but it doesn't bother me; I'm very adaptable and don't mind trying different things.
How are the four habitat requirements met for the house mouse? What else can you learn about the house mouse from this story? If a house mouse found its way into the
students' dream houses, could it stay? What could they do to make their dream house less inviting to a house mouse?
What's for Dinner?
Now that students are familiar with the habitats of these pest species, challenge them to identify the single most important factor that leads pests into our homes — to find
food. Most pests we find in the kitchen, living room, or basement are just plain hungry. Complete the activity "Tasty Paste" in which students list all the items in
their homes that could be considered dinner to a pest.
Activity — Tasty Paste
Write the following list of items typically eaten by cockroaches in homes on a chalkboard, white board, or overhead projector. Ask students to brainstorm other items that cockroaches might like to eat and, using the background readings provided, add things that other pests like to eat as well. Where are these items stored in their homes? Would their homes be inviting to a hungry cockroach or other pest? Choose a few of the items and have students suggest ways they could protect them from being eaten by a pest.
Cereals
sugary foods
meat products
cheese
beer
leather
hair |
wallpaper
artwork
paper documents
postage stamps
draperies
paper currency
books |
book bindings (they like the paste beneath the binding!)
plants
soft fruits such as strawberries, mangos, and bananas |
As an extension, note that some pests, like bed bugs and mosquitoes, make their meals out of us and not food and other items in our homes. Discuss the physical properties of blood
and why these species depend on it. Make comparisons to other animal species that feed on blood such as leeches and bats.
Pest Life Cycles
All species experience a life cycle. It is the certainty of birth, growth, reproduction, and death that all living things share. Humans and other mammals have relatively simple
life cycles — beginning life as babies, growing larger until becoming adults, and dying. Insects, however, experience unique life cycles involving the process of
metamorphosis, which means "change." Most insects experience either complete metamorphosis or
incomplete metamorphosis.
In complete metamorphosis there are four stages — egg, larva, pupa, and adult. An adult female lays eggs, which hatch into larvae. The larvae do not look like adult
insects — they usually have a worm-like shape (caterpillars, maggots, and grubs are all insect larvae). The larvae molt, or shed their skin several times as they grow
larger. Finally, they pupate, or make cocoons around themselves, and stay inside while their bodies change into an adult form. The adult breaks out of the cocoon and is ready
to reproduce and begin a new life cycle.
In incomplete metamorphosis there are only three stages — egg, nymph, and adult. An adult female lays eggs, which hatch into nymphs. Nymphs look much like adult insects but
usually don't have wings. The nymphs molt 4-8 times, stopping when they reach adult size and finally grow wings.
Activity — The Metamorphosis of Pests
Discuss the concept of life cycles with students, using humans and pets as examples. Have students share what they know about different types of life cycles. Introduce the term
metamorphosis if necessary and outline the two types — complete and incomplete. Use the two diagrams,
Incomplete Metamorphosis of a Dragonfly and
Complete Metamorphosis of a Lady Bug, as visual aids. Assign small groups of
students to research the life cycles of the following pest species — Indian meal moth, German cockroach, Bed bug, House ant, mosquito, and Paper wasp. Have each team produce
a poster or booklet with drawings of each species' life cycle stages. Species should be classified according to whether they undergo complete or incomplete metamorphosis.
Challenge students to look for answers to the following questions as part of their research.
- Which type of metamorphosis is experienced by most insects? (Approximately 88% of known insects undergo complete metamorphosis and 12% undergo incomplete.)
- Are there any insects that show no metamorphosis? (Yes — they are called ametabolous insects. The immatures look exactly like the adults except for the presence of
reproductive organs. The silverfish is an example.)
- What is the term used to describe the different stages of larval or nymph development as they molt? (instar)
- How much time does it take for each species to complete its life cycle? How many generations will it experience in a year?
As an extension, discuss molting in greater detail. As an immature insect grows, it forms a new, flexible skeleton beneath its existing exoskeleton. When it's ready to molt, it
takes in extra air to expand itself and split open the old skin. Then it crawls out and the new skin begins to harden. To demonstrate this, blow up a balloon, leaving room for
more air. Clamp the open end invice grips or using a strong clothespin, chip clip, or binder clip, so that later you can blow more air into the balloon. Then cover the balloon
with a thin layer of paper mache and let it dry. Once dry, remove the clips or vice grips, being careful not to release any air, and blow more air into the balloon until the
"exoskeleton" splits open.
Readings
Indian Meal Moth
Indian meal moths have been invading human stores of grain for thousands of years. Native to Asia, they most likely evolved out of and benefited from the emergence of agriculture
around 10,000 to 12,000 years ago, which followed changes in climate associated with the retreat of the last ice age.
Today these moths make their homes among all sorts of grain products, including flour, corn meal, dried fruits, bird seeds, graham crackers, nuts, powdered milk, chocolate,
candies, and pet food.
The larvae web together the flour with strands of silk and feed for about two weeks. The full-grown caterpillars then crawl up out of their edible homes to
pupate, emerging 30 days later as a small gray and reddish-brown moth.
German Cockroach
Cockroaches are scavengers and will eat just about anything they encounter. They have been on earth for as many as 350 million years — long before dinosaurs came and went.
No one knows for certain where they originated, although it is likely to have been in a tropical region of Asia or Africa. They are highly adapted for survival, preferring a
humid environment and living in dark burrows. They are typically active at night, and are unlike most insects in that their exoskeleton is coated not with a waxy layer but a
greasy one. This characteristic enables cockroaches to slide into narrow cracks and crevices.
Cockroaches are so adaptable that they are able to survive even in winter by exploiting small microclimates where the temperature is higher than the ambient temperature. Such
habitats include garbage dumps, were decomposition releases heat, cavities below ground that are adjacent to heated basements and other structures, and areas around sewage pipes.
Cockroaches in the "wild" will eat plants, insects, fungus, and algae.
Bed Bugs
Unlike house mice, Indian meal moths, and cockroaches, bed bugs do not follow our food into our homes, they follow us! They are a member of a group of insects that feeds on the
blood of birds and mammals. Before bed bugs discovered humans, they fed primarily on bats living in caves. When humans began to occupy these same caves, the bed bugs adapted to
feed on them, and were carried with them and spread as humans moved about and interacted with other groups. Increased world trade finally brought them to northern Europe about
500 years ago.
Bed bugs range in size from about 6-10mm long. They are so small that they are easily transported from one house to another in furniture and clothing. Once in a house, bedbugs
can hide almost anywhere and spend their days hidden in cracks and crevices in walls, furniture, behind wallpaper and wood paneling, or under carpeting or in mattress seams.
They tend not to range far and can survive more than a year without feeding.
It is very difficult to distinguish between species in the bed bug family (Family Cimicidae), and while each species tends to have a favorite host, most will readily feed on any
available bird or mammal.
Odorous House Ants
More than 10,000 species of ants exist worldwide. However, fewer than 10 are considered major pests in the United States. Different ant species vary greatly in their physical
characteristics, behavior, and food preferences. They are social insects and generally live in large colonies below ground or in trees. An ant colony may have one or many queens,
depending on the species, developing immatures, and lots of wingless workers. Most of the ants we see are worker ants, foraging for food that will be brought back to the nest to
feed the queen, immatures, and other workers. They are tireless scavengers and will feed on a wide range of foods, including liquid sugars such as nectar and honeydew, sweets,
greases and oils, starches, seeds and plants, insects and other sources of protein. Odorous house ants are native to North America and can be found almost universally across
the continent. They nest in the soil beneath sidewalks or in piles of things such as lumber, firewood, bricks, and trash. While they can form nests indoors — in walls or
beneath the floor — they usually enter homes simply on a quest for food. Ants use chemical substances called pheromones to communicate between members of their species.
When an ant finds a food source she leaves a chemical trail on the ground to lead her and the rest of the colony back to the food, which is why ants are often seen marching along
in single-file lines.
Mosquitoes
Like bed bugs, mosquitoes are insects that have evolved to require bird, mammal, or even reptile blood to complete their life cycle. They can be found worldwide, from the tropics
to the Arctic. Female mosquitoes need the rich protein found in blood to build and nourish their developing eggs. Males feed primarily on nectar and other plant juices. While
female mosquitoes will readily follow us into our homes in search of a blood meal, they cannot live indefinitely indoors. The immature stages of mosquito reproduction require an
aquatic environment in which to hatch and develop. Any source of water, either flowing or stagnant, is a potential breeding site for a mosquito.
Paper Wasps
Wasps are insects belonging to the order Hymenoptera, which consists of sawflies, horntails, wasps, ants, and bees. Some 15000 species of wasps have been identified on earth,
including 4000 in the United States. Of these, 15 are known as paper wasps. Paper wasps are social wasps whose nests consist of paper-like cells and are built under protective
structures. In the wild, this is usually under branches of trees and shrubs. However, human structures provide ideal nest sites such as eaves of homes, under decks, in vents,
and attic rafters. Nests are made from scraping fiber from plant stems, boards, and dead trees. The fibers are chewed up and mixed with saliva to form a pulpy building material,
which when dry, feels like paper. Paper wasps are often confused with hornets or yellow jackets. Paper wasp nests have exposed cells while hornet nests are cells surrounded by
a cocoon of papery envelopes (like paper mache).
In springtime, single queens begin to construct new nests. Throughout the summer, as the nest becomes more and more active, female workers forage for insect prey, nectar, and wood
pulp for nest construction, building new cells onto the edge of the nest, and caring for the brood and nonworking adults of the colony. In early August, reproductive forms begin
to emerge — males and new queens — and soon begin to leave the nests and cluster. Mating takes place and with the onset of winter the males die off and the females
search for suitable places to hibernate. Adult female wasps will overwinter in cracks and crevices in trees, stumps, underground, anywhere they are protected from the
elements — including walls, attics, false ceilings, and chimneys. Come spring, the wasps do not always crawl out the same way they crawled in, and will wind up buzzing around
the living room!
Field Observations
Activity — Moth or Butterfly?
Moths and butterflies belong to the order Lepidoptera. They are flying insects and share similar life cycles and anatomy. However there are differences. Invite students to
observe moths and butterflies in their backyards or in a park. Butterflies typically fly by day, while moths are mostly night-flying. Butterflies can be found feeding on the
nectar of flowers or drinking from puddles on the ground. They will also be attracted to fermenting fruit or molasses placed on a dish. Moths can also be attracted with baits
of sugar, molasses, and fruit, although it may be easier to use light. Moths are disoriented by lights and will often fly towards them. At dusk, have students hang a white sheet
outdoors and place a black light or lantern in front of it for several hours. Observations can be made either that evening or the next morning as many of the moths will have
laid to rest on the white sheet for the day.
Look for the bright colors and clubbed antennae on butterflies. At rest, they hold their wings closed or together, upright over their back. Moths do not have
clubbed antennae, and the antennae are usually filamentous or feathered. Most moths rest with their wings folded, rooflike, over their back. Finally, moths in
general are typically less colorful than butterflies (but there are exceptions in both cases).
Activity — Bed Bugs and Bird Bugs
Modern homes tend to be better sealed and sanitized than homes occupied 50 years ago or more, and consequently bed bugs are less common than they were then. However, their
occurrence is on the rise. Discuss their behavior with students and if necessary, have students use a metric ruler to get a sense for how small a bed bug can be (6-10mm).
Bird bugs are relatives of bed bugs and prey upon their hosts in essentially the same way as bed bugs upon humans. Many backyard birds that make nests around homes, such as
swallows, martins, and bluebirds, are parasitized by bird bugs. As a service project, have students identify nearby nesting houses of bluebirds and purple martins, and volunteer
to clean out the nesting materials that may be infested with bird bugs. Before disturbing a nest, however, be certain that it is not in use. Students can also sprinkle a small
amount of diatomaceous earth in nesting houses to discourage future infestations.
Activity — Ant Trails
Locate an ant colony or a trail of active ants. Look for small mounds of dirt, which are the entrances to nests. (Some ants such as fire ants can sting you, so avoid any ants
that are not black. Also avoid large mounds of dirt with red ants nearby—that may a fire ant colony.) Ants can also be found under stones or logs. Find a hard surface
nearby, such as a sidewalk, and have students place a small amount of honey a few feet away from where the ants are active. Observe the ants and record how long it takes for a
foraging ant to locate the honey. Eventually the ant will return to the nest and recruit others to return to the honey — by leaving a chemical trail for them to follow.
Once the trail has been established, and there are several ants actively traveling along the trail, choose a student to rub a finger across the trail to remove the pheromone.
How do the ants react? Do the ants eventually repair the trail? How long does it take? Experiment further by placing different food sources, such as vegetable oil, peanut
butter, and sugar near the active ants and determine which food source is preferred.
Activity — Mosquito Hunt
To observe developing mosquito larvae and pupae, search for natural breeding grounds in the days after a rainfall. These include streams, ponds, lake edges, swamps, marshes,
puddles, snail shells, pitcher plants, and tree hollows. Eggs can be laid singly or can be connected together like tiny rafts. Eggs hatch into larvae that are known as
"wigglers" because as they swim, they wiggle their tails from side to side. The larvae grow larger by feeding on algae, bacteria, and organic matter, and eventually
molt to become pupae. Pupae do not move around, but rather live suspended from the surface of the water, breathing air through tiny respiratory trumpets, like straws. Pupae are
known as "tumblers" as when they are disturbed, they tumble chaotically in somersaults. After a few days, mosquito pupae give way to the emerging adult mosquito.
Given the many diseases carried by mosquitoes, discuss with students their responsibility in limiting the ability for mosquitoes to reproduce. It is virtually impossible to
eliminate mosquitoes from any habitat, but some species can be controlled. The easiest way to do this is to dump out and remove any objects that contain standing water from
their backyards or the schoolyard. These include buckets, tire swings, planting containers, clogged roof gutters, and anything else that can hold water for more than five days
(ample time for there to be enough bacteria and algae to sustain developing mosquito larvae).
Activity — Wasps & Bees
Many people fear the sting of a bee or wasp, which is justified as allergic reactions can be painful and sometimes life-threatening, but it is important to note that these insects
rarely sting maliciously or at random. It is usually a defense mechanism against individual attack or any disturbance of an active nest. Encourage students to observe bees and
wasps in the wild, to become comfortable distinguishing between them and to ease their fears. Physically, bees appear to have hairy bodies while wasps are smooth-looking. They
also prefer different types of food — wasps feed on protein, such as spiders and other insects, but are also scavengers and will buzz around garbage cans and picnic sites.
Bees primarily feed on pollen, nectar, and honey. To find paper wasps in the spring, look for the queens building nests under the eaves of buildings, collecting wood pulp from
old exposed pieces of wood, or collecting water from a muddy spot at a puddle or edge of a pond or stream.
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