April 6 - Kakadon't, Lichtfield-Do

The "Top End" of Australia is better known for Kakadu National Park and Arnhemland beyond. Host to thousands of Australians and Europeans during the official holiday season (which begins in about 3 weeks time), the Arnhem Highway running East clogs with huge numbers of cars, 4WD's, buses and campers (called "caravans" here). Less-well travelled, yet a worthy alternate is Litchfield National Park to the South of Darwin. Plenty of accessible waterfalls, and secluded pools, and no saltwater crocodiles to ruin a good swim.

We arrived in Litchfield today well ahead of the holiday crowds that will soon come. Entering the park we became quickly aware of just why most stay away at this time of year. In several places water was running river-fast and river-deep straight across the paved roads; all of the unsealed 4WD tracks were gated shut and inaccessible. The recent rains had fully flooded the town of Katherine just to the South.

Our hike, from Greenant Creek to the falls was hot - searing hot, and humid too. Moreover, the path, a little overgown and marked with a sign that it was closed due to heavy rain as well as cryptically unspecified "other dangers", obviously hadn't been passed through by anyone else for some time. The way was barred, over and over, by the thick webs of large spiders, each with a death-head mark on its dorsal side. We typically prepare for each bush-walk with the usual gear: sturdy boots and hiking socks, long pants, collecting supplies, and the very necessary web-stick. Just any old stick picked up off the ground that is long enough to be waved constantly in front so as to catch invisible spider silk before it engulfs your face and neck in its sticky embrace.

Near the top of the hike, in the vicinity of the falls (an uncrossable swollen torrent in light of the rains), we did our best to drag our feet through the thick grasses. One of the Park people had suggested on the phone that this spot was "filthy" with leeches the last time he'd been up there. A forest fire had burned through the site sometime in the last year or two. Fires are a natural and essential component of forest succession. They sweep through returning to the soils many of the nutrients locked up in dead wood and dried leaves. In many forests fires are required for certain seeds to properly germinate. The notion that all forest fires must be put out as soon as they are spotted is a myth created more for the benefit of the timber industry than for the health of a natural forest. Here, and given that the region has among the highest incidents of lightning strikes anywhere on the planet, fires are clearly quite common. As a result, the understory is sparse and open, much like Kruger National Park in South Africa (where it's elephants, not just fires, that keep the area well open).

Juli did eventually retrieve one lone leech from her leg (left) which looks to be yet another specimen of Neoterrobdella australis. It is often useful to have multiple specimens of a species from multiple locations. This kind of variation in space can be accompanied by variation in color patterns or morphological characters, knowledge of which is crucial in terms of fully characterizing a species. Also, for DNA work, it can be useful to know how much genetic variability there is within a species across its geographic range.

Looking at the photograph of the leech on Juli's leg, you can see the stereotypical feeding position. Back sucker attached (to the lower right) and oral sucker spread out making a firm seal (to the upper left). Note the pronounced arching of the "neck" region of the leech. This is evidence of the strong pharyngeal muscles contracting. It's these muscles that are pumping Juli's blood deep into the stomach pouches of the leech. A close up view in real life reveals the rythmic pulsations of that arched neck as well. Had we let it continue, the body of the leech would begin to glisten as it pushes out excess water so as to concentrate the precious red blood cells until it had grown to the size of a grape.

The forecast for tomorrow is clear and sunny, so we're unlikely to be in for massive swarms of leeches at Fogg Dam.