Signs of Spring 13: Leaf Insects and Glacier Mice!

Giant leaf insect. Photo by B. Dupont. Wikimedia Commons

Audio of leaf insects and glacier mice

Most of us imagine that Nature is strange, but, to use the structure of a famous quote by Walter Heisenberg (or maybe Arthur Eddington, there is some disagreement about the origin of this insight), Nature may actually be stranger than we CAN imagine! A good example of this “imagination gap” concerns new insights into leaf insects and some rolling balls of moss on glaciers called “glacier mice.”

Leaf insects (or “walking leaves”) are a group of insects represented by 30 species (in 6 genera) that are all contained in the taxonomic family of Phylliidae. Leaf insects are found in forests and shrublands of South and Southeast Asia, Australia and on Western Pacific  islands from Papua New Guinea to the Philippines. These insects really do look like, and act like, leaves, and their elaborate camouflaging is a very effective protection against potential predators and also against entomologists! A number of leaf insect experts admit that have studied these organisms exclusively from captive and preserved specimens, and state that they have never actually seen a live leaf insect in the wild!

Antonio Pigafetta Monument. Cebu City, Philippines. Photo by Defenestrated Juan, Wikimedia Commons

The first recorded report of leaf insects was by Antonio Pigafetta, a scholar and naturalist traveling with Ferdinand Magellan on his circumnavigational voyage of the Earth back in the early 16^th Century. His description of them must have triggered a great “imagination gap” in his European readers. On the island of Cimbonbon in what is now the Philippines, he came across these “walking leaves” and wrote: “In this island are found certain trees the leaves of which, when they fall are animated and walk …. I believe they live on air.”

Leaf insects do not, of course, live on air. They eat actual leaves especially the leaves of eucalyptus and acacia (the trees on which they primarily live). Captive leaf insects, especially if eucalyptus or acacia leaves are not available, are typically fed “bramble” leaves (the leaves of raspberry and blackberry plants).

A very interesting thing about leaf insects is that a number of their genera are made up of species that only have individuals of a single gender! Some of these species only have individuals that are female,  while others only have individuals that are male. Reproduction in the “female-only” species has been ascribed to “parthenogenesis” (the development of embryos from unfertilized eggs) which is an uncommon but widely reported method of reproduction in a variety of animals. No one, though, has come up with a reproductive mechanism for the “male-only” leaf insect species!

Which gets us to a recent delivery of leaf insect eggs to the Montreal Insectarium.

Phyllium asekiense. Photo by Dragus, Wikimedia Commons

The Insectarium received a clutch of thirteen, tiny eggs that had been laid by a wild-caught leaf insect (Phyllium asekiense) from Papua New Guinea. The eggs were sent to the Montreal Insectarium because of the Insectarium’s prior success in rearing and breeding two other species of leaf insects. The incredibly rare eggs were nurtured with great care and attention by the researchers at the Insectarium, and five of the thirteen eggs hatched into nymphs.

The nymphs were then reared under carefully controlled conditions (and fed bramble leaves, by the way!). Three of the nymphs survived and proceeded on through their sequences of growth and molts. One of the surviving individuals grew into a typical, green, wingless, leaf-shaped P. asekiense individual which was, like all known P. asekience individuals, a female. The other two nymphs, though, were different. They grew into stick-shaped individuals and even sprouted wings. Amazingly, these nymphs took on the form of leaf-insect species that was from an entirely different genus (Nanophyllium), and these individuals, like all individuals in the genus Nanophyllium, were males.

Nanophyllium (males). Photo by R. Cummings, Zootaxa

The transformational quality of this “aha-moment” was spectacular. Why did the species in the Phyllium genus of leaf insect not have any male individuals? Because its males were classified as a species in an entirely different genus! Why did the species in the Nanophyllium genus of leaf insect not have any female individuals?  Because its females were being classified as a species in an entirely different genus! All of the elaborate physiological steps in Phyllium’s hypothesized parthenogenetic reproductive biology sequence were thrown out the window, and it was no longer necessary to speculate about how an all-male species could reproduce. The stick-like, male P. asekience flew from eucalyptus tree to eucalyptus tree seeking leaf-shaped female P. asekience. Their reproduction from there on was as normal as most sexual activities are!

In a paper published in the journal ZooKeys (September 17, 2020) the Montreal Insectarium researchers and their collaborators at City University of New York described the hatching outcome of these P. asekience eggs and established a new, united species name for the taxonomically split male and female leaf insects: Nanophyllium aeskience.

As the New York Times reported it: “He was a stick, she was a leaf, and together they made history!”

Glacier mice. Photo by franek2, Wikimedia Commons

In 2006, Tim Bartholomaus, a glaciologist from the University of Idaho, came across something unusual on the surface of the Root Glacier in Alaska. The glacier was covered with small, chipmunk-sized balls of moss rolling about in a slow but deliberate manner. These “glacier mice” (a term used in a 1951 Journal of Glaciology article by Jon Eythorsson of Iceland) were spongy balls of various types of moss that are thought to have formed around some dirt or dust deposits on the surface of the glacier. Their rolling motion is thought to ensure relatively equal surface exposure to sunlight and allow photosynthesis by the mosses on all side of the ball. The “herd-like” movement of the moss ball group, though, is still an unexplained phenomenon.

The moss balls move about an inch a day. Experiments by Bartholomaus and his research group showed that neither slope, nor wind or sunlight direction could explain the movement patterns and directions of the “moss herds.” They also determined that the moss balls were each isolated, biotic communities that contained tardigrades, worms and abundant microbial microflora (their research was published in Polar Biology on May 14, 2020).

“They are extremely engaging,” says Ruth Mottram of the Danish Meteorological Institute in reference to the glacier mice. “It’s very hard not to think of tribbles from Star Trek.”

Glacier mice, though, hopefully have a much slower rate of reproduction than Star Trek tribbles! We don’t want Spaceship Earth to become overwhelmed with moss balls!

Ah, tribbles on ice! How nice!