Although my entomological interests focus on katydids and other orthopteroid insects, a few years ago I started paying a closer attention to lantern bugs (family Fulgoridae), large insects remotely related to cicadas, which feed on plant nutrients that flow inside tree trunks. Lantern bugs have very long, stiletto-like mouthparts, which allow them to pierce the bark and tap into a rich stream of juices in the plant’s vascular tissue known as the phloem. This liquid is exceptionally rich in sugars, but it also contains small quantities of proteins and minerals, and it is mostly the last two that the insects are interested in. Consequently, lantern bugs end up with a huge surplus of water and carbohydrates in their diet, which they need to get rid off, and they do so by producing copious amounts of a sugary liquid known as honeydew. Other insects, such as aphids and scale insects, also produce honeydew, and they expel it slowly, in large droplets that accumulate at the tip of their abdomen. This makes it easy for other animals, ants especially, to come and lick it off – after all it would be a shame if all this sugar went to waste. Often, in return for the sweet treat, ants defend their “cattle” from predators.
But until recently a similar relationship was not known to occur between lantern bugs and other animals. The reason was simple – unlike aphids, which produce a slow, easy to collect stream of honeydew, lantern bugs shoot honeydew out of the abdomen as a jet of tiny droplets that fall a great distance away from their bodies. I was able to measure the speed with which the honeydew was expelled by these insects, and it turned out to be between 0.8 and 1.7 m/sec (2.6-5.6 ft/sec.) No animal, it seemed, was capable of tapping into this nutritious but elusive resource – imagine trying catching beer cans flying with the speed of 60 miles/hour (if we adjust for differences in size and taste preferences.)
Now we know, however, that the story is far more interesting. Together with my friend Kenji Nishida, a great Japanese entomologist and photographer, we have discovered that there exists an entire suite of organisms with unique behaviors that allow them to collect lantern bugs’ honeydew. We did our work in Costa Rica, primarily in the lowland to mid-elevation rainforest of the Atlantic part of the country. We discovered that there was a number of species of blattodeans (fascinating cousins of praying mantids and termites), who tapped the abdomen of lantern bugs with their front legs or maxillary pals, and were rewarded with a stream of honeydew that went directly into their mouths. The most astonishing part of this behavior was that occasionally we would see two or three blattodeans of different species forming a line behind a single lantern bug, patiently waiting for their turn! This unexpected politeness makes a lot of sense: a commotion of large insects fighting for access to a lantern bug would very likely spook the shy and skittish animal, and in the end nobody would get anything.
We documented a similar behavior in several species of moths, another group of frequent visitors to lantern bugs. The moths were able to catch individual, flying droplets of honeydew with their long proboscis and, like the blattodeans, sometimes formed a well-mannered line behind the insect.
Every now and then we would see a lonely ant looking wistfully at a lantern bug, but ants are simply too small to be able to catch the fast-flying honeydew, and never did we witness them being able to feed directly on the jet of honeydew droplets. We assumed that this bountiful source of sweet pee was forever beyond their reach. As it turned out, we were wrong. But to find out how ants manage to get the lantern bugs’ honeydew you will need to tune in tomorrow for the exciting conclusion of “The Mystery of Flying Honeydew!”
Update: Read the conclusion of the mystery.