Why is this swan plant unmolested?
Not just my gardenNewshub, a New Zealand television and radio news service, this week released an item headed, Where have all the monarch butterflies gone? Here is part of what it said. 'A survey of 340 Kiwis by the Moths and Butterflies of New Zealand Trust showed three-quarters of people are worried about a decline in the species. Half of the respondents said they had seen virtually no eggs, caterpillars or chrysalises in their gardens. Jacqui Knight, a spokesperson for the Moths and Butterflies Trust, says the decline could be to do with pests. "Predators like wasps and ants are killing them and the introduced South African praying mantis eat the caterpillars as well," she told Newshub on Wednesday.' Not just New ZealandWhen we think of monarchs beyond New Zealand, the vast and amazing North American wintering migrations we've seen in print and film probably come to mind. But research reports in the last few years are causing alarm. Here's an extract from a National Geographic story late 2018. 'The epic 3,000-mile monarch butterfly migration may become a thing of the past. Each fall, monarchs travel from their summer homes in the northern U.S. and Canada to winter habitats in California and Mexico. But the 2018 Western Monarch Thanksgiving Count found that the number of west-coast monarchs spending the winter in California had plunged to only 20,456 butterflies—a drop of 86 percent since last year. And the number of eastern monarchs overwintering in Mexico this year has dropped 15 percent since last year, for a total decline of more than 80 percent over the past 20 years according to the National Wildlife Federation.' What's the cause of this decline? Scientists think of the shortage of milkweed in pastures, about climate warming pushing the monarchs further north and thus increasing the length of journey and about the widespread use of pesticides. Pretty - but of any use?
Unusual characteristicWhen we do have monarchs in our garden, our cat, Snowpaws, chases them, knocks them out of the air and carries them inside. Sometimes they are dead but often they are alive and I reinstate them in a safe corner out of sight. She doesn't eat them. I've often wondered why. As I read during this week to find out more about monarchs I learnt that they are toxic. In New Zealand monarchs most commonly lay their eggs on swan plants. Wikipedia tells me that swan plant (Gomphocarpus physocarpus), is a species of milkweed and that milkweeds contain cardiac glyocsides, a toxin. The caterpillars as they chew voraciously, absorb this poison and carry it through to the adult. It's a defence mechanism. Does my cat sense the danger? Did she eat one once and decide, not again! Helping
The Monarch Trust sells swan plant and other milkweed seeds. So maybe we can all fill our gardens with plants on which these butterflies lay their eggs. We'd bring colour to our gardens and even help to halt the sixth great extinction. □ References: for links please click the red print Monarch Butterfly New Zealand Trust Science Learning Hub/Pokapu Akoranga Putaiao Newshub Where have all the monarchs gone *American National Park Service Sixth Great Extinction – see my post 17 May 2019 – in archives in sidebar click May 2019 John McInnes Friday 24 January 2020 ###########
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