Beetle Burn

For those with Sarracenia pitcher plants in the Dallas area, we’re rapidly coming up on that time of the year where the plants start slowing down and slipping into winter dormancy. In the meantime, though, the plants take advantage of the light, warm temperatures, and available insects as much as they can. Autumn is traditionally when Sarracenia plants produce their largest, brightest and most vibrant pitchers, and this coincides with many prey insects needing to finish their life cycles before impending cold kills them. Alternately, many insects, such as paper wasps, are now at loose ends: their nests have produced all of the new wasps that they’re going to produce, and one or two of those wasps will find a good spot in a woodpile or compost pile to hibernate and perpetuate the species. The rest, though, will wander off from the nest in search of food. Adult paper wasps predominately feed on nectar and other sweets, and they face increasing competition from moths, bees, flies, and every other insect facing starvation as flowers die off or go to seed. As October ends, the voluminous nectar produced by Sarracenia becomes about the only source of nectar in the area, and many insects that would otherwise stay away find themselves caught at the bottom of a pitcher, buried among both the still-living and the dead.

A point of further research on Sarracenia growth is exactly how much additional nitrogen and phosphorus plants get from insects caught at the end of autumn. While many of the pitchers grown the previous spring die off when the plant goes into dormancy, the autumn pitchers may look a bit ragged over the winter, but they still remain green into the next spring. This is a vital part of that dormancy: every last photon those pitchers can catch over the winter contributes to a storage of starch in the plant’s rhizomes, allowing enough energy to bloom once winter is over and then produce the first spring pitchers. The surprising part isn’t that they stay green even in remarkably cold weather: during last February’s week-long Icepocalypse, temperatures that killed so many other plants freezerburned the tops of pitchers at the Triffid Ranch growing area but left everything below them intact. What’s surprising is how, well, juicy those pitchers were. When trimming back severely damaged fall pitchers at different times over the winter, not only were so many of those pitchers completely packed with trapped insect corpses, but they dripped impressive amounts of what could be called either “compost tea” or “insect broth” out of the cut ends, A note to grad students seeking a research paper topic: check exactly how much of this carnivore compost tea is produced over a winter, how much nitrogen and phosphorus is in that digested soup, and how much of a difference in growth this makes to the parent plant in spring.

As mentioned before, the main insects trapped are nectar-eaters: bees, wasps, flies, moths (much more so with Sarracenia leucophylla pitchers, because of their fluorescence under moonlight), male and female mosquitoes, and ladybugs. (Some may have issues with ladybugs and other beneficial-to-humans insects being caught by pitcher plants, but the overwhelming majority seen on an anecdotal basis in Dallas-area pitchers are of the Asian lady beetle, Harmonia axyridis, which are an invasive pest. And so it goes.) It stands to reason that the nectar would attract other animals attracted to sweets, limited only by the size and diameter of the pitcher attracting them. And when the pitcher is large enough to handle really large prey, things get interesting.

Over the last few weeks, a Sarracenia leucophylla hybrid intended for upcoming plant shows started producing really impressively sized pitchers, with one pitcher with a mouth nearly two inches (5.08 cm) across. That pitcher opened approximately two weeks ago, and then bent in half and fell over in a storm. The cause of that failure was from what I euphemistically call “bee burn,” In native environments, Sarracenia process trapped prey by drawing up water in their pitchers both to drown prey and to encourage bacterial action that digests the insects and allows the residue to be absorbed through digestive glands on the inside of pitcher. When the humidity is extremely low, as tends to be a problem in North Texas in October, the plant cannot draw up enough water to process trapped prey, meaning that it rots and kills off portions of the pitcher wall. (I call it “bee burn” not only because the main causes are from collections of bees or wasps caught all at once, but because bees and wasps have strong enough jaws to tear a hole through the damaged pitcher wall and escape. This can make displaying plants at events extremely entertaining.) A quick observation confirmed that the pitcher failure was caused by just that.

The surprising part was that the pitcher wall had actually ruptured when it folded over, revealing the exoskeleton of the insect causing that case of bee burn. As opposed to the expected large wasp, a glint of metallic green peeked out. What had this pitcher caught that contributed to its failure?

Whatever it was, it was big, at least in comparison to most of the insects caught by a typical Sarracenia pitcher.

At this point, both the corpse and the surrounding pitcher wall had dried to the point where a dissection of the pitcher side was easy, and most of the corpse popped out.

The victim wasn’t immediately obvious to most, but it was one I recognized. It was a particularly large Cotinis mutabilis, a local scarab also known as “peach beetle,” “green June bug,” and “figeater beetle”, the first and last common names coming from its attracting to ripe or overripe fruit. This last summer, because of the unusual rains in August in particular, was a good one for a lot of fruit trees, especially peaches, and a neighbor’s peach tree became quite the target for local squirrels. Since the squirrels are really good about plucking a fruit, taking three bites out of it, dropping it, and getting another, this brought out a following wave of peach beetles to clean up the mess. A few turned up in raincatcher meshes after heavy rains in August, suggesting that they had as good a year as the peach trees, and apparently one laggard in October decided to check out the sweet scents coming from this pitcher and trapped itself.

The good news is that the beetle turned to soup, but not before its decomposition damaged the pitcher plant. The better news is that at least it was a peach beetle and not one of the local ox beetles. Considering a typical ox beetle’s strength, I’d be surprised if even a late-season pitcher would be strong enough to contain it.