Saturday, November 20, 2010
Listening to the delicate shower of detritus as I walked around the boardwalk at Corkscrew Swamp Sanctuary, I felt the crunch of cypress needles underfoot as they fell to the floor boards, along with a substance that looked like brown sugar. As I travelled deeper into the bald cypress forest, the powdery substance became more noticeable and my attention was drawn up to a scattered flock of birds eating something in the canopy. My camera revealed the yellow billed cuckoo, Coccyzus americanus, picking off small white furry caterpillars from the limbs. At first I just saw one but then more arrived until I was made aware that a feasting was going on all around me; caterpillars eating cypress and cuckoos eating caterpillars. Every year around this time the trees are fed upon by caterpillars known as webworms that will eventually morph into moths starting the whole process over again. They form webs in the trees around the leaves and eat until they are ready to pupate. This is also the time of year that the migrating warblers start arriving. The warblers must have been in a different part of the sanctuary taking part in a feast of their own because the cuckoos had the caterpillar food market cornered. Normally, the white “hair” on the caterpillar acts as a deterrent to predators but the cuckoo snatched them up. Normally a solitary bird, they were arriving one after another. Not only an interesting sight but the cypress fragrance together with the scent of bayberry from the wax myrtle mixed with our cool dry air was reminiscent of winter holidays. What a contrast to the muggy hot days of summer! This weather and this view is a wonderful gift that I will feast on for the remainder of the season.
With the waxing of the moon has come some glorious weather here in SW Florida and some spectacular migrating butterflies. This one is called cloudless sulphur, Phoebis sennae, traveling down from the north in search of warmth and food. Senna ligustrina, this butterfly’s host plant has emerged from the seed bank and thrived in the garden. This plant is still blooming and there are plenty of nectar plants around to nourish the adult butterfly. This summer the plant was covered with these caterpillars, eating both the leaves and flowers. As they ate the flowers their color turned from green to yellow and vice versa when they ate the leaves.
But I’ve noticed something else in my quest for connections. I am fascinated by extra floral nectaries, EFN, and this plant has them at the base of each leaf stem. To me it resembles a modified stipule. Nectaries are usually associated with the flower, secreting a sweet liquid to insure pollination. But these appendages also secrete sugars with other nutritional compounds and have nothing to do with pollination but they help to preserve the flowers. The tip of the gland is yellow or orange while the base that attaches to the stem is green. Ants are travelling and congregating around them. I have read that the ants will attack the larvae but I haven’t seen this onslaught yet. Interestingly, when the eggs are laid they look white and pitcher shaped. As they mature they turn yellow like these nectaries. I haven’t seen any eggs since August.
The ants were absent when the caterpillars were eating the flowers this summer but they are abundant now. Do the nectar producing glands respond to stress in the plant producing more nectar, attracting more ants? Now, I am seeing the flowers fertilized and seed pods forming. If ants are preventing the butterflies from flourishing on this bush are they laying them on a cassia instead, an alternative host plant without EFN? Or will they forego breeding here and return north in the spring? Obviously, I need to examine this relationship between host plant and butterfly more closely.