Everyone is on the bandwagon to help save the Monarch. And rightly so – though there are Monarchs elsewhere, our North American Monarch is the only one in the world that is a mighty migrator. It seems everything about our Monarch is unique from the Mexican winter roosting sites to migration.
I applaud everyone who has planted a butterfly garden and especially planting milkweed. I am not being pessimistic because I do feel every concerned person planting with intent to help these butterflies is awesome. But, I think we need to realistically look at this multifaceted issue and really concentrate our efforts to maximize our results. This amazing creature is almost at the point of no return according to the latest population studies. Since the mid 1990’s, 90% of the Monarchs have vanished. We do not have too many chances left to get it right.
Before I give recommendations to help rally the Monarch, we need to look at its unique biology and life cycle to fully appreciate all the natural and man made obstacles facing this winged wonder.
Let’s look at egg and caterpillar survival rates in the wild. Over the course of her lifetime a female Monarch will lay up to 500 eggs. Usually monarch survival is much higher in captivity than the wild, where the predators and other factors result in the death of 90% of the eggs laid by the female. It is absolutely staggering to analyze all the limiting factors. Climate effects eggs where in very dry conditions eggs will not hatch. The presence of aphids also plays a role in survivor rates where a few aphids on the host plant do not hurt the monarchs. Many aphids are tended by ants, and the ants will kill monarch larvae. Therefore, aphids have an indirect negative effect on the monarchs.
By large, predators, parasites and diseases have relatively small effects on monarch numbers. The main cause of the wide fluctuations appears to be the weather. Winter storms kill millions of butterflies in their winter roosting sites while summer droughts in their breeding grounds limit the amount of milkweed and nectar. Even simple rain storms account for the fatality of 70% of the eggs.
There is absolutely no doubt that the caterpillar host plant, milkweed, plays an important role to the survival rate of caterpillars. How? Chemicals from the milkweed plant make the caterpillars flesh distasteful to most animals. Due to the thick, white sap containing a lethal brew of heart poisons (cardenolides) which produce vomiting in low doses and death in higher ones. Caterpillars have also developed eating strategies concerning milkweed where, apparently, the caterpillars eat younger leaves that have more cardenolides than older leaves. Caterpillars pinch the stem of a leaf with their jaws before nibbling on the actual leaf.
For all the odds stacked against monarch caterpillars maturing to breeding butterflies, they have developed an interesting feeding behaviour/strategy. At a sign of danger, usually leaf vibration caused by the landing of a bird, the caterpillar immediately curls up and drops to the ground playing possum in the tall weeds and grasses. Here is the interesting dilemma – the caterpillars have ill equipped sense organs to find milkweed at a distance. They have a well developed sense of taste but must actually come into contact with milkweed before they can identify it. Remember, the caterpillar must get back onto a milkweed plant or starve. That is why the female butterfly, while egg laying, chooses to deposit her eggs on milkweed growing in clumps rather than solitary plants growing far apart. This increases the caterpillars survival rate by allowing a fallen caterpillar to get back up on a milkweed quickly.
Relatively new on the horizon is OE (Ophyrocystis elektoscirrha). It is a deadly parasitic protozoan that only affects monarchs and queen butterflies. The parasite is spread through spores that cling to the wings of the butterfly. Infected adults are weakened by the protozoa developing inside them, and in this condition are unlikely to survive the winter. The butterflies also pass spores from one to another during mating and female butterflies shed spores from their wings onto milkweed leaves while laying eggs. The hatching larvae ingest the spores and become infected.
So I hope you now understand what I said at the beginning of this article, ‘But I think we need to realistically look at the issues and maximize our rescue results.’ I am narrowing my recommendations to what we can do right here, right now in the monarchs breeding area. I could write another article on the winter roosting grounds dilemmas and migration perils.
We have been pointing an accusing finger at Mexico’s wintering grounds for many years but habitat loss, in breeding areas, is the number one villain. Milkweed has fallen victim to skyrocketing use of the herbicide, Roundup, on Roundup ready corn and soybeans planted on more than 150 million acres of land in the US. Also, what milkweed that is left is not necessarily the best milkweed for monarchs. Monarchs have evolved to be able to tolerate toxins in milkweed. However, several studies have shown milkweed species that have very high levels of toxin are actually harmful to the monarchs and the caterpillars actually do best on species with moderate amounts of toxins.
Plant milkweed until all the plant suppliers scream that they are sold out! And specifically plant SWAMP milkweed. It is less toxic to caterpillars especially during hot, dry summer months. Also, research is showing that caterpillars dining on swamp milkweed are less vulnerable to OE. Now here is your reality check. A well established swamp milkweed will accommodate the eating demands of 3 to 4 hungry caterpillars. A first year store bought swamp milkweed will feed 1 caterpillar. So if you want to really help the monarch you must plant LOTS of swamp milkweed.
Location, location. Sunny, warm, slightly breezy locations maximize caterpillar health. Of course, there is always room in your formal gardens for milkweed – but we are going to have to take 1 giant step forward. The ditches.
We have sprayed and cultivated and cut roadside ditches into submission in Southern Ontario. Ditches are ideal habitat for monarchs. Usually the shape of the ditches allow for water accumulation which results in less stressed, more healthy, milkweed during drought. They are usually bright, sunny places – great for healthy caterpillars. Let’s stop mowing grass right out to the roadside and replant them back to their natural state. They are lovely ecosystems in their own right. Get the swamp milkweed back into all the ditches and be sure to prominently post signs, ‘do not cut, do not spray’. I can’t stress enough about getting non sprayed milkweed back out into the natural environment – AND IN HUGE QUANTITIES.
Be sure to remember to plant the milkweed in large clumps to maximize caterpillar survival rate. Incorporate leaf litter into all your plantings. Caterpillars ready to metamorphosis will be looking for safe hiding places to transform in.
There is still lots more to discuss but I will save that for Part 2, next month. Let’s issue a challenge to one another – how about 30 + milkweed planted per garden or ditch by every concerned person. Remember, think BIG or we will not realize any real population growth and time has almost run out. Are you up for the challenge?