An online resource based on the award-winning nature guide

Monarch Butterfly

Monarchs Splitting Exoskeleton For The Fifth And Final Time

In the Northeast there appears to be an amazingly large number of Monarch larvae this year, and most of these larvae will complete their metamorphosis by transforming into a beautiful green chrysalis. Once mature, the larva, or caterpillar, wanders about and finds a suitable spot (usually protected and stable) to spend the next two weeks hanging precariously in the wind.  It then spins a silk mat in this location, and puts a silk “button” in the middle of the mat.  It clasps the button with its last set of prolegs (it has three pairs of true legs, and five pairs of so-called prolegs) and spends about 18 hours hanging in a “J,” with its head down, preparing to split its exoskeleton for the last time and reveal the chrysalis within it.

Ba Rea, a Monarch specialist (and publisher of my children’s book, Milkweed Visitors), informs her “Monarchchaser’s Blog” (https://monarchchaser.wordpress.com/about-monarchs/) readers that even though the visible changes between the larval and pupal (chrysalis) stages of a Monarch are sudden, inside the caterpillar these changes are taking place gradually and long before we can see them.  “The parts that will transform the caterpillar into a butterfly are present from the time that the egg hatches.  Inside the caterpillar are “imaginal disks.”  As wonderfully fanciful as the word imaginal sounds, it is actually referring to the adult stage of the monarch which is called the imago.  These disks are the cells that will become the butterfly’s wings, legs, proboscis and antennae, among other things.  By the time the caterpillar is half an inch long its butterfly wings are already developing inside it.

After eight to fifteen days, the adult Monarch emerges from its chrysalis and heads towards Mexico (butterflies that emerge after the middle of August migrate). It is the great grandchildren and great great grandchildren of these migrating monarchs that will return next summer.  (Photo: Monarch hanging in a “J” from Jewelweed, also known as Touch-Me-Not — not the sturdiest of plants to hang from!)

Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.


Caterpillars Eating & Molting

The larval stage of a butterfly or moth is spent doing little but eating.  Only as a caterpillar will these insects have chewing mouthparts, and they waste no time in using them. As they eat, caterpillars increase in size and their skin (exoskeleton) becomes tighter and tighter, as it doesn’t grow larger.  The caterpillar grows a new, larger exoskeleton underneath the outer skin and then sheds, or molts, the old one. Most caterpillars molt five times.  At first, the new exoskeleton is very soft and not very protective, but it soon hardens. The shed exoskeleton is often eaten before the caterpillar ingests more plant food.

There are names for the caterpillar’s stage of development in between each molt, called “instars.”  When the caterpillar hatches from its egg, it is referred to as a “first instar” caterpillar.  After its first molt, the caterpillar is referred to as a “second instar,” and so on up until the exoskeleton is shed for the final time, revealing the chrysalis (if it’s a butterfly).

The Monarch in the photograph is a very new 4th instar instar caterpillar (see antennae which haven’t hardened).  It has shed three times.  Its third exoskeleton (which it has just shed) is on the milkweed leaf behind the caterpillar. To see a real-time video of a Monarch molting go to   https://www.youtube.com/watch?v=EbHyq3RwtxI.

(Thanks to Otis Brown for his keen eye in finding this Monarch caterpillar before it ate its just-molted skin.  Also to Ba Rea ((www.basrelief.org) for her instar confirmation.)

Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.

 

 


Survival Through Mimicry: The Viceroy Butterfly

The survival of Viceroy butterflies in all of their life stages is significantly enhanced by mimicry.  A Viceroy egg resembles a tiny plant gall.  Both larva and pupa bear a striking resemblance to bird droppings.  And the similarity of a Viceroy to a Monarch is well known. For years it was thought that this mimicry was Batesian in nature – a harmless organism (Viceroy) mimicking a poisonous (Monarch) or harmful one in order to avoid a mutual predator.  However, recently it’s been discovered that the Viceroy butterfly is as unpalatable as the Monarch, which means that  mimicry in its adult stage is technically Mullerian – both organisms are unpalatable/noxious and have similar warning mechanisms, such as the adult butterfly’s coloring.

Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.


Monarch Butterfly Larvae Are Cannabalistic

The very first meal that a Monarch Butterfly caterpillar eats is its own eggshell.  In order to hatch, it eats its way out of the egg, and then polishes off the remainder of the eggshell.  It then starts to wander around the leaf and if it finds another Monarch egg, it will start to eat it.

Female Monarch Butterflies lay 300-500 eggs over two to five weeks of egg-laying. Normally, a Monarch only lays one egg at a time (on the underside of a tender, young milkweed leaf).  It is fairly rare to find more than one egg on a leaf, or even on the same plant.  After a female lays an egg, several seconds up to a minute goes by before she lays another egg (referred to as a refractory period). During this time she usually moves on and finds another milkweed plant on which to lay the next egg.  This lapse of time between the laying of each egg probably evolved to discourage the laying of multiple eggs on one leaf and to encourage the dispersal of a female’s eggs on different milkweed plants so as to decrease the chances of cannibalism occurring.

According to Dr. Lincoln Brower, renowned Monarch entomologist, a cluster of Monarch eggs on any given milkweed leaf indicates that either milkweed is in short supply, or the female that laid the eggs is either sick, very old or she has been flying for a very long time and several eggs have matured.

Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com  and click on the yellow “donate” button.


Viceroy vs. Monarch

8-18-18 MONARCH vs. viceroy1To clarify yesterday’s post on mimicry, here are the Viceroy and Monarch, side by side. Note the horizontal black line across the hindwings of the Viceroy.  The (larger) Monarch lacks this line.

Naturally Curious is supported by donations.  If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com  and click on the yellow “donate” button.


Maybe A Great Year For Monarchs?

7-31-18 _U1A4131

I have no idea what the status of monarch caterpillars is in other parts of the country this year, but at least in parts of Vermont and New Hampshire, they are plentiful!  Two on one plant — just like the old days! (Thanks to Sadie Brown for NH input.)

Naturally Curious is supported by donations. If you choose to contribute, you may go to https://naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.


Stink Bugs Preying On Insects

7-13-18 stink bug2 _U1A1686

Shield-shaped stink bugs (Pentatomidae) are fairly distinctive looking and smelling. Their common name comes from the presence of scent glands that open on their thorax, discharging pungent compounds over a wick-like surface near the bug’s hind legs. These compounds serve as a chemical deterrent for would-be predators, and also as an alarm for other stink bugs.

About a third of the 200 North American species of stink bugs are predaceous – they actively hunt and kill their prey. (The other two-thirds are plant feeders.) After spearing the prey with its piercing mouthpart, or beak, the stink bug injects digestive enzymes into its victim. These enzymes help liquefy tissues in the body of the prey and a muscular pump in the head of the stink bug enables the bug to suck nutrient rich liquid from its prey. Many predaceous stink bugs are major predators of webworms, tent caterpillars, Colorado Potato Beetles and a number of other insects that are considered garden pests. Unfortunately, non-pest species, such as the monarch caterpillar (see photo) are also subject to stink bug predation.

Naturally Curious is supported by donations. If you choose to contribute, you may go to https://naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.