A Neotropical Savanna

I have been going over the notes I made for the sandpaper plant that I watched bloom in January and February. It seems to me that are some astounding synchronies between flower “behavior” and insect behavior, so I’ve decided to summarize what I found.

There were two massive blooms, separated by a three-week period, and the sequence of events was the same each time. Here’s the chronology. All events – both flower development and insect activity – occurred about 30 minutes earlier in the day for the second bloom than for the first, so ranges of time are given.

Before sunrise – Flowers are just barely open and the stamens are barely exposed.

At sunrise - A few bees arrive.

Thirty minutes to an hour past sunrise – Flowers are fully open and the bees are swarming. (You may need to wait for the movie to load.)

The bees are collecting pollen and no doubt distributing it as well. The petals are as wide open as possible to attract the bees to the flowers, and the stamens (pollen-bearing male parts) and the pistil (female part leading to the ovary) are fully exposed to bee activity.

One and a half hours past sunrise - Petals curl back. Weevils arrive, some bees leave.

The petals curl back before they drop off. The bees act as if this curling were a signal to start leaving.

Two and a half to three hours past sunrise - Petals dropping. Bees mostly gone. Weevils swarming and mating.

It has been suggested that the weevils may deposit their eggs in the pistil so their larvae may mature within the flower’s ovary. When the fruit ripens and the seeds form, the young weevils will eat the seeds. This idea needs to be tested, but the weevil behavior here is suggestive.

Three and a half to four hours past sunrise - Petal drop nearly complete. Sepal cups, stamens and pistil remain. Weevils remain.

If the weevils are indeed preparing to deposit eggs, the absence of petals is not an issue for them. The sepal cups now serve as a platform for walking around.

Five to six hours past sunrise - Sepal cups begin closing. Weevils remain. (Please pardon the label. Weevils are a form of beetle, of course.)

Even as the sepal cups close, the stamens and pistils are still easily visible to the small weevil and, if they are depositing eggs, that can still be done at the last minute.

Eight to ten hours past sunrise – Sepals completely closed. Occasional weevil remains.

If that last weevil is looking for a pistil to deposit its eggs, it’s out of luck.

The closed sepal cups will now act as protection for the developing fruit. Soon after taking this picture, I plucked a sepal pair off the plant and tried separating it. The sepal “resisted” being opened. Once I released my grasp on the cups they sprang quickly back into place. Two days later when I repeated the experiment, the sepal cups were “frozen” in place. I could not separate them at all but had to slice them apart.

To me, this sequence is remarkable. The flower goes through its development, from open bud to closed sepals, within an eight-hour period. The period from the time the bud first opens to the time the petals are fully extended is very short – about an hour and a half. During this time bees find the flowers, swarm to collect the pollen, and leave.

It’s worth noting that insect activity was much greater for the second bloom than for the first. At the height of bee swarm during the first bloom, I estimated that (very roughly) 50 bees were buzzing around at a time. During the second bloom, roughly 1,000 bees were there during the swarm. I failed to come up with a good estimate of weevil numbers, but I had the impression that they, too, were more abundant the second time around. It’s as if the bees and the weevils were alerted to the blooming of this plant the first time around, and the word spread. By the second bloom they were ready to pounce.

If indeed the weevils are laying eggs in order for their young to eat the seeds after they develop, then it’s surely no coincidence that the weevils “let” the bees have first dibs at the pollen. After all, the flowers must be fertilized in order for the fruit to develop.