Complex Interactions in the Milkweed Patch

He’s back!  This handsome caterpillar, perhaps the same one we observed yesterday, was found among the Milkweed plants today.  He was discovered as the group searched around the leaves looking for Ladybird Beetle larvae, adults, eggs, and exuviae (the empty exoskeletons of larvae who’ve molted) – all very common in this area of the garden. The Ladybird Beetles and larvae are feeding on the many orange, yellow and green aphids who are in turn feasting upon the milkweed’s leaves. To make matters even more interesting, the aphids are being bravely guarded by large black ants, who harvest and consume nutritious ‘honey dew’ from their protected flocks of aphids.

This little milkweed patch is a perfect arena for students to do hands-on learning, not only about insect life cycles, but also about plant defense compounds (the dripping, white sap of a broken milkweed leaf can vividly capture youngsters’ attention), camouflage vs. warning colors, confusing morphology (both ends of the monarch butterfly larva wave prominent black ‘antennae’ – as a result, it’s difficult to quickly locate the insect’s head).

Most significantly perhaps, here children can actually witness the cooperative / mutualistic interactions between ants and aphids, or those between Ladybird Beetles and the Milkweed plants themselves. (The Milkweeds are spared excessive damage when the Ladybird Beetles gobble the greedy aphids who would otherwise devastate the plant’s large leaves.)  This situation, in which the beetles help the plants survive the aphids’ munching, is a fine and memorable example of a “trophic cascade” – a phenomenon in which one creature in a food web benefits another by actually consuming some of the second creature’s potential predators.  Insect-eating songbirds consuming leaf-eating caterpillars offer another readily observable example of this type of interaction.  In this second case, the birds are helping those wondrous tall, woody plants – the trees.  If we looked a little more carefully at the relationship between these beings, we would also recognize that the trees in turn are helping the birds by providing them with lofty, safe perches in addition to places, and sometimes even materials, for constructing nests.  And these are just a few of trees’ multiple gifts to birds and other animals.

This is the sort of true and powerful information that children deserve to know.  It’s vital that they see and understand from an early age that both cooperative and competitive relationships are essential to the dynamics of Nature.