Christmas Bells

Christmas Bells
Christmas Bells - Blandfordia nobilis

Tuesday, April 01, 2008

Cordyceps - "Vegetable Caterpillars"

I mentioned recently the visit by the Sydney Fungal Studies Group (SFSG) to the Robertson Nature Reserve. Here are some photos of the most bizarre fungi we found. They are called Cordyceps gunnii. Firstly this is the Cordyceps "in situ", in the ground, with its fruiting body emerging above the forest floor.The Cordyceps story is pretty gruesome. Are you ready for this? They are known (loosely) as "Vegetable Caterpillars". There is nothing vegetable about them, for they are fungi, (which are not plants).
The bit on the right hand end of the Fungus is the mummified body of the caterpillar (grub) stage of a Swift Moth. You can actually see the bumps on the body which are the "pro-legs" of the Caterpillar. (Click on the photo to enlarge it.)

The life cycle of the Caterpillar starts with the adult moth laying an egg (that must be on or close to the soil surface). Then the tiny grub hatches out of the egg, and starts to feed, and presumably to burrow down into the ground. Apparently they feed on the roots of rainforest trees, deep in the soil. This image (below) is a composite image, and is quite long, if you click to enlarge it, you will get a full-size image. Given that the fungus spreads its fine spores in the air, and therefore, down onto the forest floor, I assume that the grub must be infected by the spores either through contact, or I imagine, more likely, by ingesting vegetable material which has spores on them (i.e., leaves on the forest floor).

The grub must then continue on its merry way, growing, eating and burrowing further and further down into the soil. Eventually the grub achieves full size, of about the size of a human finger (it is a big grub). At that stage, the fungus starts to reach its own life-cycle climax, still feeding on the flesh of the caterpillar. There is a theory that the infection by the fungus triggers the grub to move closer to the soil surface (so that the fungus does not have to reach too far in order to get to the surface (to spread its spores though the air). Eventually the fungus kills the caterpillar (grub). It weakens the grub, as it absorbs all the nutrients in the body of the caterpillar, and effectively "mummifies" the body of the caterpillar, replacing the original tissues with its own tissues. Then the fungus matures completely, and develops its fruiting body, in order to spread its spores.

The "fruiting body" of the fungus grows as a long thin organ emerging from the head of the (by then) mummified caterpillar. Once the tip of the fungus reaches open air, the long stem changes in character, and it develops the spore-bearing organ. It is from there that the fungus then spreads its spores, ready to infect a hatchling grub of the Swift Moth. That completes the life-cycle of the Cordyceps. This is a close-up of the spore-bearing section of the Cordyceps gunnii.This fungus is an Ascomycete, and does not have gills, but has very fine pores (in the dark greenish end of the fungus - at the left hand end, in these photos) through which it spreads its pores. Here is a collection of these fungi, including one which was a "double-header". One was extremely long, with a small fruiting body. The theory is that the grub was too deep for the fungus to successfully grow out to reach the air. The effort to grow that far, apparently weakened the fungus and it produced a very small fruiting body, relative to the shorter stemmed ones, which did not need to produce such long stems. All fungi collected in the course of the SFSG visit were returned to the Robertson Nature Reserve, (after recording, and photographing), so that their spores might continue to be spread in their natural environment.

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