The one thing about plants that we take for granted is that they cannot really hurt you. Sure, some are full of toxic compounds and can be deadly poisonous if ingested. Others are covered with nasty spines or irritating hairs, and a tree can fall on your head during windy weather and crack your skull. But we feel pretty secure in the fact that no plant can hunt and eat you. Things would be very different, however, if we weren’t some of the largest animals on the planet.
I was having these thoughts last Sunday when I went looking for another singing insect, the minute Sphagnum ground cricket (Neonemobius palustris), one of a few species of New England acoustic orthopterans that I had never managed to get a recording of. I decided to try looking for it at Ponkapoag Bog in the Blue Hills Reservation, about 10 miles S of Boston. Almost immediately after stepping on the wooden planks that run through the soggy Sphagnum bog I started hearing the characteristic, high-pitched tinkling of those small crickets. But it took me a while to find one, and I only managed to do so after a considerable amount of crawling on all fours, waving a shotgun microphone to pinpoint the source of the sound. Eventually I located one individual in a sunny spot, deep in a clump of red and green moss. As I was recording his song, I also marveled at the idyllic setting of this species’ home. “What a great place to live for an insect”, I thought, “no predaceous ground beetles, no centipedes, water and food plentiful.” But then I heard behind me somebody say “Look honey, bladderworts! They catch and eat aquatic insects.” Right, I forgot about the killer plants.
Bogs are strange communities, not quite aquatic, not quite solid ground. The constant presence of low levels of water leaches nutrients from the soil, making the habitat extremely poor in minerals, particularly nitrogen. Some plants can fix atmospheric nitrogen thanks to a symbiotic relationship with cyanobacteria in their root system, but most need to find another way, and some do so by becoming carnivorous. I looked around and just a couple of feet from where my cricket was happily singing sat a gaping mouth of the pitcher plant (Sarracenia purpurea). The plant was half hidden in the moss, the lower lip of its pitcher conveniently at ground level, its entrance inviting to any cricket looking for a hiding place or something to eat. The bottom of the pitcher was dark with half-digested bodies of insects, a few still floating on the surface. The lip’s surface was covered with backward-pointing spines, making it easy for an insect to walk in, but virtually impossible to leave. It was as if you walked into your local grocery store, only to realize that you are in the Little Shop of Horrors.
In addition to bladderworts and pitcher plants, Ponkapoag Bog is a great place to see honeydews (Drosera rotundifolia). Unlike pitcher plants, which lure and drown insects, sundews actively grab them with their sticky, glandular tentacles that cover their modified leaves. They mostly catch small midges and gnats, but I saw one plant successfully capture a pretty big damselfly using two of its leaves at once. Of course the insect must first touch the plant, but once it does, it is pretty much doomed as the leaves curl and immediately start digesting the prey. I often complain that our huge body size prevents humans from appreciating most of the richness and beauty of the natural world, but carnivorous plants are another reason to think that maybe it is not such a bad thing after all.