After I found the dead flies and aphid on the stems, I decided that I must investigate further. The next afternoon, I collected a few critters from the garden; a pill bug, a centipede, a millipede, an ant, a tiny plant bug. I put each one in a plastic container with a few stems and flowers of London Pride, and watched to see what would happen.
|2 mm. bug, on broom stalk.|
A sad sight; the centipede touched a stalk, and immediately started to writhe, then slid off to one side and lay trembling all afternoon and evening. The pill bug walked over one stem, and spent the rest of the afternoon grooming himself, cleaning the glue off his legs and antennae. So did the plant bug. But the millipede died in a couple of hours. A second one died the same way; a control in a container with no London Pride was fine. Only the ant was unaffected.
|London Pride flower, with trapped aphid|
I watched a couple of aphids on a stem; they were alive when I first saw them, but completely stuck to the red balls. They struggled to release one leg, only to have another touch down and be trapped; more attempts left them attached by antennae, body, and legs.
This all brought up more questions; the aphids probably died due to being glued, and having their breathing spiracles clogged. But the millipedes? They hadn't seemed to struggle at all, and had left the stalk long before they died. Was the plant poisoning them?
I asked Google; an image search was most helpful. I found many plants with similar structures, many more than I would have expected. Of course there were the carnivorous sundews, with their beautiful, deadly traps, large enough to see without a lens. Compare these:
|London Pride flower stalk.|
... with these:
|Sundew Drosera capensis. Image from Wikipedia. By Noah Elhardt.|
Small prey, mainly consisting of insects, are attracted by the sweet secretions of the peduncular glands. Upon touching these, the prey become entrapped by sticky mucilage which prevents their progress or escape. Eventually, the prey either succumb to death through exhaustion or through asphyxiation as the mucilage envelops them and clogs their spiracles. Death usually occurs within one quarter of an hour. (Wikipedia)
I was surprised to find how many other plants are protected the same way. The list includes geraniums, squash, the mint family, rosemary, coleus, tobacco, some peppers, catnip, roses, potatoes, tomatoes, and more.
The glue sticks are called glandular trichomes, or hair-like appendages that produce enzymes or essential oils. Some of these oils are toxins, others attract insects (and cats), some are glues.
Glandular trichomes on potato and tomato leaves release phenols and phenol oxidizing enzymes which react to form a sticky substance which hardens to entrap small–bodied insects. Aphids, for example, get coated with sticky phenols when they land on these plant surfaces. In the struggle to escape, they disrupt a second type of trichome which releases polyphenol oxidases (PPO). The PPOs oxidize the phenols into quinone, entrapping the aphids like hardening of cement, resulting in its death. (Plant Glandular Trichomes)
Oh, the pill bug, ant, centipede and plant bug? They recovered once they were away from the London Pride, and I released them and the control millipede, with my apologies for the trouble I had caused them.