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Monarch Caterpillar

Summary: Unlike many damaging caterpillars, the Monarch caterpillar's diet consists almost entirely of milkweed leaves, so they will not pose a threat to your garden or yard.

Hooray for small favors! At last a caterpillar that won't destroy my landscape plants and trees. The Monarch caterpillar eats milkweed leaves and nothing else. Farmers love having the Monarch as a guest to rid fields of the persistent milkweed plant.

The sap of milkweed leaves contains a chemical called cardiac glycoside. This chemical is stored in the caterpillar's body. If a predator tries to attack the monarch caterpillar, it will taste this repulsive, poisonous chemical. Ingestion of the Monarch caterpillar usually results in illness.

The day before the monarch caterpillar emerges the egg turns black. After the caterpillar emerges from its shell, it eats it! It grows and grows during its time in the larval stage of its life, which is about 14 days. In fact, a monarch caterpillar can grow over 2,000 times its original mass! Its main responsibility


during this time is to eat plenty of food. This weight gain is important in determining how big the monarch will be as a full-grown butterfly. The large amount of milkweed leaves allows the insect to store a lot of lipids that are useful when it is an adult trying to survive the winter.

A monarch caterpillar goes through five different stages called “instars.” The caterpillar grows bigger and molts its skin throughout each stage. The official term for a caterpillar's skin is “cuticle.” The caterpillar also has an exocuticle, which is a waxy substance that protects the insect from losing water.

The body of a monarch caterpillar is fascinating. It has three pairs of true legs connected to its thorax, and it also has a few pairs of prolegs connected to its abdomen. The prolegs have tacky pads called crochets attached at the bottom.

Monarch caterpillar predators have a special technique for finding their prey. They observe milkweed leaves for damage giving a good indication that the Monarch caterpillar is present. However, the caterpillars also know how predators can find them, so they do a lot of moving from leaf to leaf, leaving no forwarding address.

Another escape tactic for the Monarch caterpillar is to use silk as a type of rope. If it senses a predator nearby, the caterpillar can crawl down to the ground by dispensing a string of silk. Like many other types of caterpillars, it will curl up into a ball and do the “play dead” routine when touched.


A Monarch caterpillar will give off certain clues when it is ready to pupate. First, it will stop eating. Second, it will move from the milkweed leaf it was living on, moving to a safer place. Finally, it will hang off a twig or leaf in the shape of a “J”. Within a day, the monarch caterpillar will form into a chrysalis. (Interesting fact of the day: A butterfly develops from a chrysalis, but a moth develops from a cocoon.)

Because Monarch caterpillars have a diet that entirely consists of milkweed leaves, they will not pose a threat to your garden or yard. They are also relatively harmless to humans. These unique caterpillars grow into beautiful butterflies, so if you see them near your home, they will be fun to observe as they go through the stages of metamorphosis.


14 Mar 2011, 12:34
I am in Bermuda. I bought a small milkweed plant and it has six caterpillars on it. Unfortunately the biggest one eats a ton and probably after two more days, I will have no more leaves on my plant. What to do? Should I go buy another plant and transfer them or should I visit the botanical garden and take a few fresh leaves for them every day? Thanks for the advice!
Ask the Exterminator
14 Mar 2011, 12:37
Personally, I would do nothing at all other than allow Mother Nature to take her course. The caterpillars will relocate to find more food without any help from you.
14 Mar 2011, 12:40
Kathy, you definitely need to buy SEVERAL milkweed plants...a growing caterpillar will eat 8 leaves per day or more! if you do not they will die. Home Depot carries Milkweed.
13 Apr 2011, 08:37
When I went to bed last night I had 3 monarch chrysalis hanging from a board on the fence (about 3 ft high) and one on a leaf of the milkweed plant as well as one cat hanging in a "J" ready to cocoon. When I woke up this morning all 5 are gone! What could have happened to them? I have 5 more chrysalis that are up high hanging off my covered patio (about 9 ft high) that were not disturbed. Does any animal eat the actual chrysalis?
Ask the Exterinator
13 Apr 2011, 10:12
Spiders and birds will attach cocoons.
Ida OConnor
04 Jul 2011, 01:21
Hi, I have a Passion Flower plant that the Monarch Butterflies love. Now I have the whole life cycle going on and I really need to know if spider's eat the chrysillas. They are very smart and fly infront of my window to let me know if a caterpillar needs help crossing the black rock on our front wall due to the fact that it gets very hot and almost cooks then like a frying pan. So I'll get them and put them somewhere that is shady. They also have been drinking outta the Humming Bird feeder lol. I just want to know if there is anything that I can do better to help these little guy's along. I had no idea that Passion Flowers attracted butterflies.
Ask the Exterminator
05 Jul 2011, 14:17
Although I cannot say for certain, I would suppose that birds, spiders and a host of other predators will eat the chrysillas. Just remember, as you "help" the butterflies survive, you are hurting birds and other species that need to feed on the butterflies.
Stacy Nourse
14 Jul 2011, 11:24
Hi, I am actually a newbie to raising catepillars indoors. I live in southwest florida. I bought those butterfly habitats and cut out the bottoms so i keep a paper towel on the bottom and just change it regularly. I've done alot of research online. I have about 47 catepillars, 3/4 of them are in chrysalis stage now. I am almost out of milkweed and i've been kind of "starving them" so to speak. I give them what I have and i even scrape off some of the stems so they have some food available. I actually have about 10 that are in their last stage and they are still eating like crazy. I don't know what else to do. My local greeneries don't have any milkweed available right now. I even went so far as to put them up on the top to see if they would just change to a chrysalis. Then I find a catepillar eating another that was hanging like a J. HELP. Not sure what I can do to save these cats. I didn't meant to raise so many. it just happened and it sounded like fun at first...but now I'm just day by day praying that they turn into a
Ask the Exterminator
15 Jul 2011, 16:13
Sorry! I cannot be of much help. I'm an exterminator, not a biologist.
17 Sep 2011, 15:19
I live in State College in Central Pennsylvania and just had an amazing experience bringing in, for the night, a Monarch. It was holding on to the chrysalis when I found it. It flew away this morning, after a gatorade, sugar suryp, soy sauce meal. She was beautiful. My question: I just found a catapillar on my milkweed. Should I try and ship it to someone futher south and west or leave it alone? I suspect it will not make it through the chrysalis stage before we have feezing temps.
Ask the Exterminator
18 Sep 2011, 08:08
I am a believer in allowing Nature to take its normal course. Return it to where you found it.
30 Mar 2012, 10:19
We have 8 cats on one milkweed and I noticed one of the babies and other adult cat were on a plant nearby. Is it ok if I moved them back? There was also another adult (missing his antennas) that had climbed on a 6ft fence nearby. Is he cocooning? I thought they cocooned on the milkweed so I moved him back as well.
Jen Jordan
07 Apr 2013, 12:50
In Texas USA and have tons of Monarch Caterpillars on my milkweed but lately when they crawl up and attach to wall they never make it into the pupa stage and just dry out as hanging cats with little silk strings hanging down? It doesn't seem like the T fly prob because they don't make it to chrystalis form. Anybody else have this problem? I have a bunch of brown dead cats hanging on my wall???
lexiana tucci
14 Jun 2013, 17:16
I wonder why they don't tell u how big the cat will grow until it grows a chrysalis?
01 Aug 2014, 08:08
Do the caterpillars make new antennae when they form the chrisalis? One of my caterpillar's antennae are laid back on it's body and look twisted together and sticky. I had observed some fighting between caterpillars I am fostering. Will these remain damaged or will they form new ones?
Ask the Exterminator
01 Aug 2014, 10:57
In order for the change from a caterpillar to a butterfly to take place within the pupa, the caterpillar begins releasing enzymes that literally digest nearly all of its own body. What’s left inside the chrysalis is mostly just a very nutrient rich soup from which the butterfly will begin to form.
05 Oct 2014, 00:18
What does a Monarch cat do at night? Are they sleeping or are they always going through a molting period if they aren't moving? Thanks
08 May 2015, 10:49
one month ago I bought 10 milkweed plants from home depot, my caterpillars died, many, many of them or they were born without being able to fly. Two weeks ago I bought 10 more plants from home depot and the same thing has happened. I called home depot this morning and expecting a call back. Of course they denied anything being wrong with their plants. obviously this is not true. I have been raising monarchs for three years now and have NEVER experienced this sad situation. Home Depot is going to call the nursery where the plants come from, now way will they admit to using pesticide.
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