What is black ice--and why is it slippery?

  • Black ice is relatively smooth, hard, and clear.
  • Packed snow eventually turns to black ice, especially when it rains, or when there's a thaw, followed by freeze.
  • You must completely remove packed snow if you want to prevent ice buildup.
  • Black ice is most slippery when water is present.   Then it can be very dangerous.  Applying sand to ice greatly improves traction.
Black ice on the roads is what sends cars spinning out of control.  On sidewalks with black ice, pedestrians fall without warning.  So what is "black ice," and how does it form?

This "black ice" formed by freezing of meltwater.  It looks bright because it's reflecting the sunset.

Black ice is no different from ordinary ice--except that it's more compact and has a smoother surface.  Here's how snow turns to black ice.


How to prevent sidewalk ice--without salt

Use the sun instead of salt!

Key ideas...
  • Prevent packing during snowfall by clearing a narrow lane--people walk there, preventing packing elsewhere.
  • Clear to full width by noon of the day following snowfall.
  • Scrape remaining packed snow so light gets through to the pavement.
  • Let the sun evaporate the rest (ice can evaporate without melting).
  • Touch up daily--before leaving for work.
Removing packed snow prevents ice


Clear sidewalk snow without salt

Prevent snow from packing down...
because packed snow turns to hard ice in a few days.

Snow blowers make things worse, because they leave a layer of packed snow.

Use a shovel with a sharp edge (or an ice scraper) to remove packed snow. The sooner you remove it, the less the ice sticks to pavement.

Shovel a narrow lane as soon as you can. People will walk there, and won't pack snow on the unshoveled portion.

Now use solar power to melt the rest! 
To disappear, ice (or packed snow) does not need to melt. It can go directly from solid to water vapor, even at temperatures below zero! It's called "sublimation."

Ice does require energy to vanish without melting. You have to scrape the snow thin enough so light energy will penetrate to the pavement. Even with thin clouds on cold days, enough sunlight penetrates to make a difference. The ice will disappear in a few days, depending on temperature and sun. Touch it up before you leave for work... the sun will do the rest.

To prevent icy patches from forming when it warms up, clear to the edge of the sidewalk between snowfalls. This way, any meltwater sinks into the ground at the pavement's edge. You don't get icy puddles on the sidewalk.

With more pavement exposed, the sidewalk area gets warmer, helping to prevent new ice--and the next snowfall is easier if the whole sidewalk has been cleared.

You have to clear your sidewalk, but you don't have to shovel your driveway, at least not right away.

Work in stages to avoid fatigue, resting between. First the central strip of the sidewalk. Then scrape packed snow. Then enlarge the width of the path. Finally, clear to the grass and chip any remaining ice.

Check the weather report. If it's going to warm up, no worry to clear snow. If a long period of cold weather is coming, be careful to prevent packed snow. Salt doesn't melt ice at temperatures below about 15F, but the sun does!

Even on hills or steps, you don't need salt. Sand works very well. You can find it in city barrels at street corners. You can buy Yaktrax to make your shoes slip-proof.

Hope this helps! HAPPY SOLAR SHOVELING !


Lecture by top expert on monarch butterflies

A lecture by Dr. Karen Oberhauser.
October 18, 7 p.m.-8:30 p.m. at the UW Arboretum Visitor Center, 1207 Seminole Highway.
"Oberhauser, one of the nation's top monarch conservation
biologists, will describe the amazing biology of migratory monarch
populations, and the work of citizens and scientists in
documenting monarch numbers at all stages of their migratory
Sponsored by the Madison Audubon Society & the WI Chapter of the Society for Conservation Biology.


Does road salt make winter driving safer?

Given the lack of progress since Madison first tried to reduce road salt use, it's time to look for new ways of viewing the problem.

As soon as a conversation about salt begins, the subject of winter road safety comes up.  Road safety seems to override any other argument.

But does salt really make winter driving safer?  We can refine this question to ask... "Do the obvious safety benefits of salt outweigh the enormous economic and environmental damage caused by salt?"

"Outweigh" implies that we have to measure--to quantify--both the benefits and costs of salt.

An obvious starter...  Are there any highway accidents actually caused by salt?

A bridge collapses


How road salt led to poisoned water in Flint, MI

It's time to recognize that spreading too much salt in Madison could have dangerous and unforeseen consequences.

In Flint, MI, road salt played a role in poisoning the public water supply.  When Flint switched the source of its water from Lake Huron to the Flint River, salt in the city's water soared from from 11.4 mg/l to 92 mg/l.  Salt in the river came largely from overuse of de-icing salt on roads.

Salt (chloride) is extremely corrosive.  It caused Flint's lead pipes to corrode, releasing lead that can cause brain damage in children.  At the home of Lee-Ann Walters and her 3-year-old son, average lead levels were measured at 2,000 ppb, sometimes exceeding the EPA criterion for "toxic waste."

Despite the increase in salt, the city did not add a corrosion inhibitor* to the water as many cities do. So both iron and lead pipes corroded, resulting in lead poisoning of many children.

Could Flint's poisoned water happen here?

Our situation is different, because Madison has replaced all its lead plumbing.  But three of Madion's shallower wells are becoming contaminated with salt (up to 37 mg/l in 2013).   The level of chloride in Lake Wingra is 130 mg/l and headed upward.  MG&E has been pumping millions of gallons of salty water into the ground with the Odana Project.

Even without lead pipes, chloride in city water can cause big problems.  The chloride corrodes iron pipes and water mains.  Flint has reported increased leaks--the corrosive water will cost millions of dollars in damage to pipes.  And when iron pipes corrode, they use up chlorine added to the water to kill bacteria.  That's why Flint had bacteria in their water--chlorine was rapidly used up after leaving the wells, leaving the water reaching consumers unprotected.

Madison's older water mains can rust from the inside and the outside. Chloride in both tap water and groundwater has been steadily increasing. Madison needs to replace half of its 400 miles of pipe.  By 2020, the annual cost of replacing or relining Madison's water pipes will be $12.7 million.

While the US does not consider chloride to be a pollutant, Canada does consider it "toxic," based on potential damage to the environment.  How long before Madison's salt reaches crisis levels? We already know salt causes billions of dollars in property damage, rusting autos, corroding bridges, and weakened parking ramps.  Now Flint demonstrates salt can have dire and unpredictable health consequences.  Our leaders should lead by taking decisive action to limit salt. 

Chloride in Madison's tapwater See p. 3. The median level of chloride in Madison's wells is 24 mg/l, ranging from 2.2 to 106 (2013).

* A corrosion inhibitor has been rejected by Madison's Water Utility, because it contains phosphorus which would also harm our lakes and streams.


Monarchs threatened by climate change in their wintering areas


Monarch butterflies roost in huge numbers during the winter only in oyamel fur trees in the mountains of central Mexico.  The fur's dense foliage provides insulation from freezing temperatures. And unlike other trees, monarchs can easily cling to the fir's tiny needles with their claws.

But as temperatures rise with global warming, oyamel furs won't be able to survive where they are growing now.  People will have to plant the oyamels at higher elevations, so the butterfly reserves will be ready for changed conditions.

That's just what Mexican conservationists are planning for now.

Find out more here.
Photos of my trip to the wintering areas in 2015.


Viewing the monarchs wintering in Mexico

Here's a brief report of my March trip to the monarch butterfly wintering grounds.  The link to Lake Wingra is that monarchs are a charismatic species that people are concerned about.  Any activities that help monarchs are also likely to help our watershed.

Goals for the trip were to see the butterflies, and to locate some schools nearby who want to exchange letters or art with schools in our watershed.

Monarchs wintering in the Cerro Pelon reserve.
Click on photos to enlarge.


Obama reveals plan to save Monarch Butterflies from extinction

Two million dollars are targeted to grow milkweed and other food plants along the Monarch's migration route.  Read more.

An official petition has been launched to have Monarchs classified as an endangered species.

Increase in winter population

"The number of monarchs overwintering in Mexico has increased from last year's record low but the population remains 80% below the historic average.

This year's population contains 57 million monarchs compared to a long-term average of 300 million and a peak of 1 billion. The clustering butterflies cover less than 3 acres of forest compared to a peak of 51 acres in 1996 and an average of 15 acres.

Half of this year's butterflies are residing in only one of the 12 traditional sites, the El Rosario sanctuary."  Source.


How to raise monarch butterflies from the egg

Look for eggs in a large garden where you see lots of monarchs.
Click on photos to enlarge.

The purpose of raising monarchs...
  • Boost populations, since there is very high mortality of caterpillars in the wild.
  • Teach people about the miraculous life cycle of butterflies
  • Provide chrysalises to classrooms, where children can view butterflies emerging.  Once people have seen the amazing life cycle of monarchs, they can't help but want to work for preservation of habitat.
  • Raising monarchs is an opportunity for children to learn firsthand many details about biology and husbandry, along with responsibility and perseverance.
Supplies needed
  • Hand lens--about 10X or 20X--to confirm you have monarch egg, and to see black head that indicates egg is ready to hatch.
  • Nearby supply of several large wild plants--to feed caterpillars
  • X-Acto knife--handy for cutting ends off leaves or plants you have placed in water, so they will continue to take up water.  Also handy for cutting a small square from the leaf, with the egg on the square.
  • Nail scissors--handy for cutting the eggs from the leaf, or for cutting stalks of milkweed for food.
  • Glue, such as for plastic airplane models--to fasten chrysalis to a matchstick, for pinning to your Butterfly tent
  • Plant mister
  • Bleach (chlorine)--for disinfecting (use 1 parts bleach with 9 parts water)
  • Plastic containers with lids--to hold milkweed leaves or upper stems of whole plants
  • Paper towel--cut a tiny strip, and use this to transfer freshly hatched caterpillar from ice cube tray to a fresh leaf.
  • Ice cube tray (white plastic)--place your leaf squares with eggs into the tray, one egg per compartment.
  • Optional: mesh container--where adults can emerge  Example

There's a fair amount of work involved.  The Friends of Lake Wingra will make it easier by showing you how--and in some cases, finding eggs and milkweed plants for food.

At all stages, you need to avoid spreading the parasitic disease known as OE.  It's a protozoan parasite carried by 6% of monarchs.  When an infected female lays an egg, a few of the spores are spread from her wings onto the egg, so the caterpillar becomes infected.  That caterpillar can spread it to other caterpillars.  Or, you could spread it with your hands, or by the brush you use to transfer caterpillars from plant to plant.

The OE parasite is harmless to humans, but it weakens the butterflies, so they are less able to migrate.  Some biologists believe this is why migration benefits monarchs.  The infected butterflies are unable to complete migration, so the overwintering adults--the ones that start the next generation--are infection-free.

You can spot some infected caterpillars because they have a "dirty" appearance, with the stripes less crisp-looking.  Or, the chrysalis may look dirty, or the emerging butterfly may appear somewhat deformed.

A monarch female lays over 700 eggs on average, yet only two need to survive to reproduce.  So a lot of mortality at each stage is expected and normal.  Don't feel bad if one of your caterpillars dies.  It's probably not your fault, and if the egg had hatched in the wild, its chances of survival would have been worse.  There are hordes of predatory insects, spiders, and birds that would love to dine on a juicy caterpillar, even if it's somewhat poisonous.  Amazingly, some of the predators have ways to deal with the poisons.  Some birds will remove the wings of an adult monarch they have caught, because most of the toxins are stored in the wings.

It takes over a month--depending on temperature--from egg-laying to emergence of the adult.  So time your monarch project accordingly.  You don't want your vacation to occur at the wrong time, or the butterflies to emerge after classes end for the summer vacation.

The monarchs you raise aren't your pets.  Raising a caterpillar is a serious contract you are making with a species in trouble.  In exchange for its freedom, you are promising to help that individual, and to help the species.  So take your role seriously.

Finding eggs

Once you see adults in your area, it may be possible to find eggs, about the size of the head of a pin.

 Eggs are creamy to yellow in color, slightly translucent, and have a distinctive ribbed structure you can see with a hand lens.  The eggs are laid on the underside of leaves, usually one to a plant (but sometimes you can find more).  Sometimes you can find eggs on seed pods.  Eggs are laid only on a plant in the milkweed genus, including common milkweed, butterfly weed, and swamp milkweed.   If you find one egg, then check other plants nearby to find more.

I was lucky to find several eggs on common milkweed in a county park in June.  But it's much more likely to find eggs if you go to a large garden with many flowers, where you can see many monarch adults flitting about.  Then examine the underside of leaves of any milkweed plant there.

Look for eggs on taller milkweed plants along the edge of a garden or prairie, or along a lakeshore or stream border.  Borders tend to concentrate the laying females.  Eggs become more common as the summer progresses.

Monarch nectaring at top of plants.
If a monarch adult is on the top of the plant where flowers are, then they are nectaring (feeding).

 But if they land lower in the foliage, then they are probably laying.  They will alternate between nectaring and laying.  Laying takes just a minute.  The female arches her abdomen under the leaf to deposit the egg.  You could quickly mark that leaf, then follow her about to wait for her next egg.  If you aren't quick enough to mark the leaf, then remember that area, and search all milkweeds in the area.

Female laying down in the foliage.
When you find eggs, how do you get them home?  If you go out waking, it's handy to carry a small container.

 I use little metal jars intended for tea samples, with holes in the screw-on lid.  When you find an egg, you can tear off a small portion of the leaf with the egg attached, and put it in the jar.  I have also put many leaves with eggs attached in the ample breast pocket of my expedition shirt.  If you don't hug anyone, the eggs will be OK if you go straight home.  The pocket is good because in that location, the eggs won't overheat; beware of leaving eggs in direct sun or in hot cars.

Incubating the eggs

Cut the eggs from the leaf with nail scissors or an X-Acto knife--so the egg is in the middle of a tiny square of leaf.  Place the egg on its square into one compartment of an ice cube tray.  We don't leave the eggs on the leaf you find them on because that original leaf will dry out before the egg hatches.

The eggs hatch after about 5 days.  At first the egg looks creamy and uniform.  About 12-24 hours before hatching, the top of the egg (away from the leaf surface) turns dark or black-- that's the black head of the caterpillar visible through the transparent egg shell.  When you see black, that's time to transfer the square of leaf to a small, fresh milkweed leaf.  That way, the egg hatches on a fresh leaf, and you don't have to transfer the caterpillar yourself.

If the egg hatches in the ice cube tray, it's easy to see the tiny caterpillar because the tray is white.  Transfer the tiny caterpillar carefully with a strip of paper towel.  Usually, if you put the paper strip under the front of the caterpillar, he will instantly attach a strand of silk to the paper.  Then you can lift him by the silk and move him to the fresh leaf.

When the egg hatches, a very tiny caterpillar emerges--hard to see without a hand lens.  It first may eat the egg shell, then it wanders off a short distance, and may begin to eat the leaf it is on.

Transfer the caterpillar
to a fresh leaf with a brush
or piece of paper towel.
Feeding the caterpillars

Keep your caterpillars on a table top that is otherwise empty.  That way, you can easily spot escaping larvae.

Keep providing fresh food, keep the container clean, mist daily, and regularly check for wandering caterpillars (or chrysalises).

At first, the little caterpillars don't seem to eat much--just tiny little holes.  But as they grow, they eventually eat a great deal every day.

Give the caterpillars fresh leaves about every other day, or as soon as the leaf wilts.  Never allow them to remain on dried-out leaves.

You can place a number of newly-hatched caterpillars on one leaf.  As they grow, they will need bigger leaves, and food more often.

Once they get larger, give them the top half or top third of an entire plant.  A portion of plant will resist drying out, and you won't have to waste time transferring caterpillars from one plant to another.  If you bring in a large stem, look for and remove any spiders or insects.

To transfer a caterpillar, use of small strip of paper towel.  If this isn't working, you can cut off a portion of the old leaf, and transfer this with the caterpillar to the new leaf.

Keep the water in your containers fresh.  To prolong life of a leaf or stem of milkweed, cut the stem end once a day.

Large caterpillars
can eat a whole leaf in a few hours.
Caterpillar excrement is called frass.
It consists of small, dry pellets--black or dark green.  The frass is odorless and harmless, but large caterpillars can produce a great deal.  To keep your house clean, place newspapers under the plant.  Then using scotch tape, turn up the edge of the newspaper to make a little fence on four sides.  This keeps the round frass from rolling away onto the floor.  Or, you can just vacuum the area twice a day.

If you are raising the caterpillars in a container, empty it out every day or so, as frass accumulates.

In the wild, the caterpillars would get the water they need from milkweed sap, or from dew and rain.  You should mist their food once a day.  If their food plants are wilted, or the humidity in your house is low, then you may need to mist them more often.

Caterpillars prefer some species of milkweed over others. Some people say they prefer swamp (purple) milkweed.

Behavior of caterpillars

It's surprisingly complex.

Larvae, even tiny ones, have a safety line--a tiny silk thread spun from their rear end.  If they get knocked off a leaf, they are still safely tethered to their food plant.  Sometimes you can use the silk thread to pick them up safely with a brush.

The larvae don't seem to mind the presence of others nearby, and the big ones won't eat the little ones.  They even seemed to get used to my presence.  While eating or moving about, they may become motionless when you enter the room--responding to the vibrations of your footfall.

They prefer the undersides of leaves, where they are hidden from predators, and safe from the drying effects of sun, or from rain and wind.

Caterpillars tend to eat in a little circle, with themselves in the middle.  It's said that this way, they cut off the area where they are feeding from the flow of sap.  The milkweed sap is sticky and rubber like, as a defense against monarchs, and also a bit toxic even to the caterpillars.  To for them, the less sap the better.  Large caterpillars may also nip the base of the leaf to stop the flow of sap, so that it hangs down.

Each caterpillar has several rhythms of activity, and they don't seem to be synchronized with the day-night cycle.  A caterpillar will eat steadily for some hours, then rest.  Then eat again.   After a while, they become inactive for about a day, in preparation for molting--shedding of their skin.  First the head capsule drops off, then it wriggles out of the old skin over several hours.  Then it will rest after shedding.  Then the whole cycle of resting and eating, then resting to molt, happens again.  They molt 5 times.

The reason I mention rhythms is that you may think your caterpillar is sick.  It might even drop off the plant during an inactive period.  If you disturb it, it will move slightly, but it won't eat.  Be patient, and probably it will resume eating soon.

The last larval stage may start to wander.
When your caterpillar is in its last skin (instar), it gets cranky and unpredictable, like a teenager. Now it may leave the plant and wander off some distance. You replace it on the plant, but it wanders off again.  It can cross a while room in a short time.  Is it tired of your lodgings?  No--it's just looking for a good place to molt into the chrysalis.  After all, it's going to be "sleeping" in the chrysalis for about 10 days, completely defenseless, and mostly unable to move.  So it's urgently looking for a very safe place.

Now's the biggest crisis in your rearing job.  The caterpillar may completely disappear.  When you walk into the room, watch your step, so you don't squash it.  Check especially under tables or counters, or in the drapes.  If you are very thorough, you'll probably find it 6-10' from where it was feeding.

To avoid wandering, place large caterpillars on a milkweed stem with many leaves, in a container with slippery sides.  Don't let the milkweed leaves touch the wall.  With these precautions, your caterpillar will probably form the chrysalis on the milkweed plant.  Using a 10-gallon aquarium with a lid is another way to keep them from wandering.

You know for sure the caterpillar is ready to form the chrysalis when it begins to hang from it's tail end in a "J" shape.  It spins a slender stalk of silk, attached to the under surface of a counter, or to the twig.  Inside the J-shaped caterpillar, the chrysalis, and even some of the adult structures, are already forming.  Within a day or so, it will shed the last caterpillar skin and reveal the chrysalis.

Chrysalis attached by a new stalk to plastic lid.
This shedding process is amazing.  You would think that the stalk of silk the caterpillar is hanging from is the future stalk for the chrysalis--but this isn't the case.  When the chrysalis had nearly wriggled free from the hanging caterpillar skin, it makes a sudden move--dont' miss it!  The chrysalis removes its tail from the hanging skin and suddenly stabs the tail onto the surface above.  Apparently this stalk-like tail of the chrysalis has some natural glue, so it sticks fast after one or more pokes.  Now the chrysalis is hanging from a new stalk, and the old silk stalk of the caterpillar, along with the old skin, drops to the ground.

If the chrysalis (also called the pupa) attaches to a kitchen counter, you do not have to remove the counter and cart it off to school.  Instead, gently cut the stalk of the chrysalis, keeping the stalk as long as possible.  You can handle the chrysalis gently (if it has hardened for a day).  Observe sterile conditions.

Use a tiny drop of plastic airplane glue or a piece of thread to attach the chrysalis stalk to a match stick.  Then, pin the match stick to the roof of your butterfly tent.   Or, you could use a 10 gallon aquarium with lid.

The butterfly can even emerge when the chrysalis is lying on a flat surface, provided there is something nearby the newly emerged butterfly can climb up.  It can only unfold and dry it's wings when it is hanging upside down with enough space.

The chrysalis undergoes many visible changes during the 9-14 days before the adult emerges. The caterpillar flesh inside the shell is becoming completely reorganized.  You can see the chrysalis slowly changing shape, and the wing cases enlarging.  A little necklace of silvery beads grows around the chrysalis.  These are the metabolic wastes of the pupa being deposited close to the shell of the chrysalis.  A few days before the butterfly emerges, you can see the orange of the wings growing brighter.  The wings get fairly bright and obvious a few hours before emergence.

Emerging from the chrysalis
Caterpillars packed for school

This is the payoff of all your work, so try not to miss it!

Butterflies tend to emerge mid-morning.  The process takes about 15 minutes (with several hours for the wings to expand and harden).  Everything must happen just right.  Your job--very important--is to provide a rough surface that the butterfly can grasp with its claws as soon as it emerges.  If the chrysalis stalk is attached to a twig, that's fine.  But if the stalk of the chrysalis is attached to something slippery, the butterfly will fall to the bottom of the container, and its wings will be forever warped.

The chrysalis splits, and the adult begins to wriggle out and expand.   It must hang freely down from the lid or twig, while it's wings first expand with blood, and then while the wings harden.  Do not handle or disturb the new butterfly for many hours while the wings harden.  Once they are hard, you may move the butterfly by gently clasping the folded wings with your thumb and forefinger.

If you don't want to use your fingers, remember that the adult has two large claws on each leg.  You can hook those claws with a twig or Q-tip, and lift it to place it somewhere safer.

The butterfly can be placed in a small mesh enclosure made for butterflies or for dirty laundry--they are available on the internet.  Example 1.  Example 2.

Releasing the adult

You can feed the butterfly for several days with honey--1 part honey to 9 parts water.  Moisten a bit of sponge or a Q-tip with the sugary solution.  The butterfly has taste receptors in its front legs.  So if you hold the Q-tip up in front of the butterfly, and encourage it to put its feet on the Q-tip, it should soon uncoil its proboscis and sip the nectar.

It's best to release the adult in the morning of the day after emergence.   It shouldn't be too cold--temperature above 55 F and wind less than 15 mph.   If during fall, mid-morning might be a good time.  Watch to see which direction it flies.  Mine immediately headed south!

If you keep the adult for several days, you will notice at first that it stays quietly where it emerged.  Butterflies are cold blooded, so their activity is determined by temperature.  As the day progresses, it warms up.  It may begin to move its wings, which helps it to warm up more.  Suddenly, it will launch itself toward a window.  From there it may fall to the ground.  So be careful where you walk.  If you plan to keep it a day or so till the weather improves, place it back on a plant where it can hang for the night.

If your adult cannot fly, it may simply be that temperatures are too cool.  Or, it's wings may have become warped during emergence--especially if it fell down or had too little space to expand.  It may be weakened by the OE parasite.  If your butterfly cannot fly, that's sad.  I would then feed it for as long as it lasts.  For me, that was about a week.  Learn all you can about its behavior.  Remember, that's the bargain you made.  Treat it the best you can, and teach others about its miraculous life.  The life of one single individual isn't what's most important.

Take in the wonder of its existence--the incredibly complex and fragile life cycle--and resolve to teach about monarchs and to improve their habitat.

Frequently asked questions

My butterfly never emerged from the chrysalis. 

If temperatures are low, it may take up to two weeks for the butterfly to emerge from the chrysalis.  Freezing (or direct sun with elevated temperatures) will kill the chrysalis.  If your caterpillar was weakened by the OE parasite (or another disease), it may not emerge, or will emerge deformed.  If the food quality was low (leaves late in season or dried out), that could weaken the caterpillar.

My large caterpillar looks sick--dark and limp and inactive.
Don't worry.  Your caterpillar may be ready to form the "J," then the chrysalis.  This is normal.  If dark and limp, and if the antennae are crooked, and if he is wiggling, he may be about to shed the last caterpillar skin to form the chrysalis.  Watch carefully--it only takes about a minute.  Smaller caterpillars are also inactive before an after molting--shedding their skins.

My caterpillar left his food and is wandering.
At any stage, wandering is a sign that (1) your food is unsatisfactory, probably dried out or dirty, or (2) the caterpillar is getting ready to shed his skin.  Before shedding, smaller caterpillars don't go far, perhaps just to the side of the vase holding the food.  But just before they form the "J," caterpillars get VERY restless.  If they have an easy way to escape, they probably will.  You need to watch them at this time.  The wandering phase only lasts a few hours.  It's a good time to give them fresh food, to make sure it's not bad food that's causing the wandering.

My egg hatched, but the tiny caterpillar disappeared.
Hatching (and just before the J) is the trickiest time of rearing, so be careful.  Possible causes of disappeared hatchlings:

  • There are predators about at night: ants, spiders, or wasps.  Eliminate predators from food plants.  Keep your caterpillars indoors.
  • The caterpillars wander and get lost in clutter.  Check eggs frequently for the blackhead stage, and transfer them before or soon after hatching to a fresh leaf.  Use a white ice cube tray where hatchlings are easy to see.  Place the tray at the top of a tall, clear drinking glass.  Check under the table.
  • Small caterpillars may wander from one vase (or food leaf) to another. 
My caterpillar don't do anything.
This is normal.  Mostly, they just eat, excrete, rest, and change their skins.  But if you watch them more closely, they have surprisingly complex behavior.  There are several cycles of resting and eating for each instar (an instar is a stage of the caterpillar's life, separated by changing the skin).  There are 5 instars.

Can I change from one type of food plant to another?
Monarch larvae eat ONLY plants in the milkweed genus.  However, if they are started on one species of milkweed, they will eat another species.  They may not prefer the new food, but they will adjust.  Changing food species could be one cause of "wandering" caterpillars.

Can I hatch adult butterflies in the same enclosure where the caterpillars are fed?
This is not a good idea, because some of the emerging butterflies may be infected with the OE parasite, even if they look healthy.  These butterflies will be loaded with OE spores, and spread them to the caterpillars.  You should sterilize your hands with hand sanitizer after you handle butterflies, before you touch anything the caterpillars use.  If you are not careful, all you butterflies could become infected.  They might then be too weak to complete the migration.