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Posts tagged “Monarch Butterfly

Monarch Butterflies Reach Wintering Grounds

Two days ago, on November 6th, the first Monarch Butterflies arrived in their 73-mile-wide overwintering area in the Transvolcanic Mountains of Central Mexico. This miraculous flight, which takes a Monarch roughly two months, can be up to 3,000 miles long. Using the sun, and most likely the earth’s magnetic field, they head for specific stands of Oyamel Fir trees, where they will cluster and be protected, unless weather conditions are severe, from extreme temperatures, predators , rain and snow until next March, when their journey north begins. (These butterflies only get about half way back to New England, at which time they mate and lay eggs. The third or fourth generation of these monarchs will reach their eastern destination.) To track the migration of these remarkable insects, go to
11-8-13 monarch butterfly IMG_6361

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Monarch Numbers Down

7-22-13 monarch IMG_1107According to the Vermont Center for Ecostudies, this spring and summer there’s been an estimated drop of 90% in the overall monarch population in eastern Canada – the most dramatic decline ever recorded. Vermont (and most likely New England in general) is experiencing much the same situation. The low numbers of monarchs are due to several factors that they have encountered along their migratory routes the past couple of years, including extreme temperatures, record drought, low nectar production by flowering plants and a scarcity of their host plant, milkweed. The cold temperatures and record amounts of rain this spring undoubtedly added to their stress.

Monarch Butterfly Migration is Underway

Monarch Butterflies have begun migrating — the peak of their migration in Central Vermont/New Hampshire is September 3 – 15. Monarchs typically cycle through four generations during the breeding season. The final generation migrates to Mexico. Those individuals emerging in late summer live much longer than the Monarchs that are around in June and July (6-9 month life span vs. 6-8 weeks). This allows Monarchs in the East the time needed to migrate up to 3,000 miles (a trip that takes roughly two months) to central Mexico, live through the winter and to begin a return trip (making it only about halfway back), mating along the way. The succeeding generations of Monarchs continue the return trip back to New England, and with luck, the great (or great-great) grandchildren of the butterflies that are migrating to Mexico now will grace our milkweed patches next summer.

Monarch Butterfly Chrysalis

Of the multitude of discoveries that every summer offers us, one of the most magical is that of  a Monarch Butterfly chrysalis.  While locating a Monarch larva is not all that difficult, especially when they are as prolific as they are this summer, finding a chrysalis doesn’t happen all that often. Most butterfly chrysalises are a rather drab brown, but the Monarch’s is a beautiful green which serves to camouflage it in fields where the caterpillars feed on milkweed and eventually pupate (form a chrysalis).  The Monarch caterpillar, when mature, usually seeks a sheltered spot under a leaf or branch where rain will not cause the silk button by which it hangs to disintegrate.  The chrysalis in the photograph is attached to a blade of grass which was anchored with silk to another blade of grass in order to make it more secure.  No matter how many I’ve seen, each one still takes my breath away.

Viceroy Butterfly

The Viceroy Butterfly closely resembles the Monarch Butterfly, but is smaller, and has a black line that runs across the veins of its back wings, which the Monarch lacks. While Viceroys don’t contain the poisonous cardiac glycosides that Monarchs do, they do contain salicylic acid due to fact that the larvae feed on willows. This acid not only causes the Viceroy to taste bad, but makes whatever eats it sick. So not only do these two butterflies look alike, but they discourage predators in the same way. This is not a coincidence. The fact that they are both toxic if eaten and are preyed upon by some of the same predators has led to their similar appearance. This phenomenon is referred to as Müllerian mimicry, and essentially it means if two insects resemble each other, they both benefit from each other’s defense mechanism — should a predator eat one insect with a certain coloration and find it inedible, it will learn to avoid catching any insects with similar coloration.

Monarch Butterfly Eggs Hatching

It appears that this may be a good year for monarchs in the Northeast, as with very little looking, you can find their eggs as well as young monarch caterpillars. Look on the underside of the top leaf or two on young milkweed plants – these leaves are tender and monarchs often lay their tiny, ribbed eggs there (usually one per plant) as they (leaves) are ideal food for young larvae. The first meal a monarch larva eats is its egg shell. It then moves on to nearby milkweed leaf hairs, and then the leaf itself. Often the first holes it chews are U-shaped, which are thought to help prevent sticky sap (which can glue a monarch caterpillar’s mandibles shut) from pouring into the section of leaf being eaten.

Invertebrate Signs

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A quick look recently at the underside of a wooden bench sitting in the middle of a nearby field revealed a multitude of signs of insects and spiders that sought shelter in this protected spot.  They included the empty chrysalis of a monarch butterfly, the flat, red egg  sac of a Phrurotimpus  antmimic  spider (look closely and you’ll see bumps in the middle  made by the eggs underneath the silk), the silk and twig case of a bagworm moth larva , and a cocoon which is housing the pupa of a moth. 

Some Monarchs Outwit Milkweed

We think of monarch larvae as being impervious to the  ills of milkweed, but they are very vulnerable when it comes to the sticky latex in the sap of their host plant.  The mandibles of young monarch caterpillars are often glued together by this latex, preventing them from eating.  Research shows that about 30 percent of monarch larval loss results from miring  in this glue-like substance.  One strategy young larvae use is to chew a near circle in a milkweed leaf, blocking the flow of latex to the enclosed surface area, which they then eat.  If a monarch survives the first few stages, or instars, of its larval life, it uses yet another strategy to circumvent the latex.  Older, larger larvae often cut through the midvein of a leaf they wish to consume, which dams the latex flow to the entire leaf beyond the cut.  Look for limp leaves as you peruse a milkweed patch.  If you find one, you may be rewarded with the nearby presence of a monarch caterpillar.

Monarch Caterpillar’s Spinneret

Unlike spiders, whose spinnerets, or silk-spinning  spigots, are located at the tips of their abdomens, caterpillars’ spinnerets are located underneath their heads.  The most prominent white structure with a black band around it is the monarch caterpillar’s spinneret, in which its silk glands are located.  The smaller structures are called maxillary palps and are antennae-like sensory devices.  Prior to metamorphosing into a chrysalis/pupa, the monarch caterpillar draws silk through its spinneret, and forms a small, well-anchored button of silk. The caterpillar clasps this button with a structure called a cremaster, located at the tip of its abdomen, from which it suspends itself upside down.  Soon thereafter its skin splits, revealing a gold-dotted, green chrysalis from which an adult monarch butterfly will emerge in two weeks.

Monarch Butterfly

This 15-minute-old monarch butterfly that emerged yesterday will live for 2 to 5 weeks, long enough to mate and produce the next generation of monarchs.  The generation of monarchs that emerges a month or more from now will live six to nine months, and not mate until next March or so – after flying  to one of about a dozen locations in the Transvolcanic Mountains of central Mexico (a flight of up to 3,000 miles) and spending  the winter.  Late summer-emerging monarchs live longer than monarchs that emerge earlier in the summer because they do not immediately expend energy on breeding and the cool winter temperature in Mexico slows their metabolism, allowing them a longer life.