Monarch Biology

Monarch Biology

What is the function of the gold dots on the chrysalis? Are they really made of gold?

Fred Urquhart first studied the gold spots on monarchs in the 1970s. He felt that the spots were involved in the distribution or formation wing scale coloration. However, the experiments that he did involved cauterizing the gold spots on the pupa, and it is possible that this process may have damaged the underlying tissue and affected the color patterns. Interestingly, all danaine butterflies (monarchs and their relatives) have metallic spots on them. A group of researchers in Germany did a careful study of the properties of these spots. They are not metallic (so they aren’t really gold), but the cells reflect light like metals do, giving them the appearance of being metallic. Other danaids have silver, copper, or gold spots.

Here are some hypotheses for the reasons that these butterflies have metallic-looking spots on their pupae:

  1. Camouflage — they could reflect colors of the surroundings and break up the shape of the pupa; they might also look like dew droplets.
  2. Warning coloration
  3. Filtering particular wavelengths of light which might be harmful to the monarchs
  4. They might not have any function but just be the result of something else in the cuticle of the insect.
How many wings do monarch butterflies have?

Monarchs have four wings. 

What do monarch caterpillars (larvae) eat? Can they eat anything other than milkweed?

In North America, monarch caterpillars rely on milkweed (Asclepias)  and a few closely related genera to grow and develop.  Female monarchs use a series of cues to find milkweed and lay their eggs on the leaves of this plant.  After the egg hatches, the caterpillar feeds on milkweed exclusively, and does not leave the host plant until it is ready to pupate.  Milkweed is known as a “host plant” for monarchs.  An example of a plant closely related to milkweed that is an appropriate monarch host plant is Cynanchum laeve (common names sandvine, honeyvine, bluevine milkweed, and smooth swallow-wort).  It is native to eastern and central U.S. and Ontario, Canada.  

Monarchs have been known to lay eggs on species other than milkweed, such as the invasive swallow-worts (Cynanchum louisea, formerly C. nigrum or Vincetoxicum nigrum) and pale swallow-wort (Cynanchum rossicum, formerly Vincetoxicum rossicum), which are members of the milkweed family (Asclepiadacea) native to Europe.  However, monarch caterpillars cannot feed on these plants and do not survive.

How many legs does a monarch caterpillar have?

Monarch caterpillars have 6 true legs (3 sets) and 10 prolegs or false legs (5 sets).

Does a monarch butterfly have 6 or 4 legs?

All insects, including monarchs, have 6 legs! The front set of legs appear much smaller on the butterfly and are sometimes hard to see, but they are there! 

How big is a monarch egg and what does it look like?

Monarch eggs are about 1.2 mm tall and 0.9 mm wide (about the size of a pinhead). They are an off-white to pale yellow color and have longitudinal ridges. 

How big can monarch caterpillars get? How many times do they shed their skin?

Monarchs go through five caterpillar growth stages, that we call instars. Each time, they shed their skin (molt) allowing them to grow larger. 1st instars are generally 2-6mm, 2nd instars are 6-9mm, 3rd instars are 10-14mm, 4th instars are 13-25mm, and 5th instars are 25-45mm.

How does the color and pattern of the butterfly wings help them to survive?

Monarch adults and larvae have aposematic coloration. This means that the bright colors of either an adult monarch or a monarch larva signal to potential predators that they may be dangerous to eat. The bright and contrasting colors of monarchs warn predators to keep away because they are distasteful or unpleasant.

How long does it take for monarchs to develop from egg to adult?

This process generally takes about one month. Once an egg is laid, it will hatch in about 3-5 days. The caterpillar stage (1st-5th instar) lasts for about 2 weeks. Finally, the pupa or chrysalis stage in monarchs lasts 9-10 days.

Why do new butterflies hang upside down?

Butterflies hang upside-down when they emerge from their chrysalis so that gravity can help them pump the fluid from their abdomen into their wings. This allows the wings to expand and dry so that the monarch can use them to fly!

How many eggs can a female monarch lay in her lifetime?

A female butterfly only lays eggs over a 2-5 week period. During this time, she probably lays an average of 300-400 eggs in the wild, although numbers in captivity are higher – about 500-700 depending on things like temperature and the conditions under which the female is kept. The largest number we’ve ever observed in our experiments was about 1100! Of course, most monarchs in the wild don’t survive the egg and larva stage, but are eaten by predators.

Why does an egg turn black/dark just before it hatches?

Just before a monarch egg hatches, the dark pigmentation of the monarch’s head capsule develops. This is visible through the translucent egg shell and gives the egg its characteristic grey dot!

How do you tell male from female in each of the life stages of monarchs?

In adults, male monarchs have a dark spot on each of their hind wings, called androconial pouches. These are thought to be significant in the courtship/mating of some species, but the function in monarchs is unknown. Females do not have these dark spots on their hind wings.

You cannot tell male from female in the egg and larva stages of monarchs.

There is a very tiny line on the female pupa that isn’t present on the male. This line is at the top of the pupa, in the abdominal segment second from the cremaster. It’s difficult to describe without showing a picture or diagram. You usually need a magnifying glass to see it, unless you have super vision!

How big is an adult monarch?

Monarchs have bodies that are about 10 cm wide (including their wings). Monarchs weigh, on average, about half a gram, this is about the weight of a paperclip. This can vary from about .27 grams (a very small monarch!) to about .75 grams (a very big monarch!).

How many times can a monarch’s wings flap in a minute?

About 5 to 12 times a second, so about 300 to 720 times a minute. (This is actually quite slow compared to many other butterflies.)

How do monarchs breathe?

Monarchs breathe through tiny openings on the sides of their bodies called spiracles. (The spiracles are in their cuticle, like our skin). The holes open into a system of tubes in their body (called trachea) that carry the oxygen all over their bodies. They don’t have lungs. This is different from the system that we and other mammals have. We breathe air into our lungs. Special cells in our blood pick up the oxygen, and the arteries of our circulatory system carry oxygen to the rest of our body.

Where can I find a monarch pupa in the wild?

Monarchs pupate on many different kinds of plants and other structures. We’ve found them on blades of grass or other plants, spruce trees, park benches, fences, milkweed plants, and garage eaves.  They rarely stay on the plant on which they were feeding, probably to avoid parasitic wasps that can use chewed leaves and frass as cues to locate their hosts.  They can crawl several meters from their host plants (milkweed). We really don’t know if there is a “preferred” plant species or other surface for pupating. 

How long do adult butterflies live?

This depends on when they live (summer or winter). It also varies a lot among individuals (just like it does it humans). In the summer, adults live from 2 to 6 weeks in captivity, and probably about that long in the wild. The ones that migrate live longer, from August or September to about April (although a lot die before this). When people hear this, they say they’d rather be a migratory monarchs, but these butterflies probably face many more risks, and are likely to have a smaller chance of getting offspring into the next generation.

Do monarchs live in other parts of the world besides North America?

Yes, monarchs are found in many places throughout the world, but they probably originated in the Americas, and were spread either with the help of humans or on their own to other places. They are found in Australia and New Zealand, and many islands east of these countries (most islands between Australia and Tahiti have monarchs). They are also found in Hawaii, most islands in the Caribbean, and even sometimes in western Europe.

How are monarchs toxic to predators?

Monarchs become toxic to predators by sequestering or storing toxins from the milkweed plants that they eat. Milkweed contains toxins called cardenolides, or cardiac glycosides, which are toxic to predators. This makes monarchs very distasteful or unpleasant to predators. Some predators have evolved ways to avoid or tolerate these toxins, such as the bird predators found in the Mexican overwintering colonies.