Life Inside Life Inside a Leaf
Posted by Richard Conniff on December 27, 2012
I often find myself hating leaf miners, mostly when I am picking spinach or swiss chard, only to find their little paths of destruction winding through the leaves that I had planned to eat for dinner.
For those of you who have not had the pleasure, leaf miners are caterpillars of a tiny, exceedingly flat character, and they meander through the sliver of world inside a leaf gobbling up everything in sight. They are the immature offspring not of any single insect group, but of flies, beetles, moths, and even some wasps. Thus calling them “leaf miners” isn’t really a taxonomic description. It’s behavioral.
In any case, you may find it hard to fathom, at first glance, why someone would travel deep into the war-torn, infrastructure-deficient, bushmeat- and-bribe-happy Democratic Republic of the Congo to discover new leaf miners.
But that’s what researchers at the University of Florida and the Royal Museum of Central Africa in Belgium did in 2008, and it cost them $250 in handouts just to get their luggage out of the airport. They also saw guns everywhere, including bubble-wrapped AK-47s as carry-on luggage on domestic flights. Was it worth it?
Some of their results, including descriptions of 41 new leaf miner species, are just out in Zootaxa. The researchers also have another 100-200 new species from the trip still to be described, according to co-author Akito Kawahara, assistant curator of lepidoptera at the Florida Museum of Natural History on the UF campus.
Despite our image of the Congo forest as a wonderland of gorillas and forest elephants, the researchers saw no large mammals on the trip. They’ve all been hunted out. Even in a national park, said Kawahara, he could hear the gunfire of poachers at night. Maybe they were going after whatever’s left of the birds.
In any case, much of the biodiversity that survives, in the Congo and elsewhere in the tropics, consists of insect life, and it is weirdly wonderful, though not conventionally charismatic.
With the familiar specialist’s love for his subject, Kawahara said that leaf miners “can be extraordinarily beautiful with colorful markings and metallic scales.” But he added: “If you think of a regular caterpillar and then you squished it and shrunk it, that’s what they look like.”
They’re typically just a millimeter thick, and 2-5 millimeters long, and with a microscope you can see right through them, Kawahara told me by phone. You can also see everything that’s going on inside them. One of the gruesome facts of life for all caterpillars is that wasps like to lay their eggs on them, so the larva can hatch, burrow inside, and feed on the living caterpillar, until eventually the adult form bursts out, alien style, and flies off, leaving a husk of dead caterpillar behind. Caterpillars have taken up the leaf-mining way of life partly to escape this wretched fate, and also to avoid more conventional predators.
That may also be the reason for all their meandering inside a leaf. I thought they just wandered back and forth eating whatever happened to be in front of them. But according to Kawahara, parasitic wasps locate their victims even inside a leaf using vibration. They tap-tap-tap till they hear or feel something that sounds like caterpillar. But all those tunnels tend to confuse and delay them. Since the wasps also have their own predators to worry about, they give up after a while and fly off in search of a more rewarding leaf.
The wasps also hunt by sense of smell, and that may explain why leaf miners stash their poop in a sort of toilet inside the leaf: Misguided wasps may end up laying their eggs on something that smells like caterpillar but is in fact a cesspool.
Sad to say, these deceptions don’t always work: “If you look at what is happening inside a leaf under a microscope, it’s just an incredible world,” Kawahara said. “You’ll see a tiny wasp larva living within a caterpillar, and another, even smaller wasp larva living inside that larger wasp larva that is inside the moth larva. It’s a parasitoid of another parasitoid. It really opens your eyes to this incredible, unknown world and makes you think, ‘What is going on here?’ It’s truly amazing.”
Interested? I just checked on Kayak, and it looks like you can book your flight from JFK to Kinshasa for under $1400. With luck, no AK-47s will be included in the price.
SOURCE: Jurate De Prins, Akito Y. Kawahara. Systematics, revisionary taxonomy, and biodiversity of Afrotropical Lithocolletinae (Lepidoptera: Gracillariidae). Zootaxa, 2012; 3594