July is the month of heat. It dominates the natural world. Heat is energy; the energy of molecular motion. It increases the rate of chemical reactions in the living substance of plants and animals. It’s been said that there is a doubling of the rate of biological processes for every 10°C (18°F) rise in temperature. As a result, there is a tremendous increase in the rate of insect propagation and the growth of herbaceous foliage, or as we see it, more mosquitoes and weeds.
As any hiker can tell you, activity taken during the heat of the day extracts significant energy. In the natural world of animals, this theme also applies. You just won’t find much activity during the day. To find the activity of the season, you’ve got to turn over a few rocks and rotting logs, where it is cooler and more moist.
Among the various creatures you may come across, you’ll commonly find sow bugs and pill bugs, collectively known as wood lice. Sow bugs have a mottled, scalloped shell, while pill bugs are dark, streamlined, and have the ability to curl up into a ball for protection. Perhaps the most interesting thing about these creatures is that they are crustaceans, not insects. These terrestrial isopods have been wildly successful, with over 5,000 species living worldwide. They are generally scavengers, in the same class as earthworms in their ability to improve soil quality.
Evolved from the marine ecosystem, many species still use a modified gill, an organ for extracting oxygen from water, while some species have supplemented it with a tube system for breathing in air.
Like aphids, balsam and hemlock woolly adelgids, succeeding generations of all females are produced parthenogenically by the mothers, which produce daughter clones of themselves. They need a male only to make sons. Additionally, a bacterium called Wolbachia skews sex ratios in many of the terrestrial isopod species. It has a feminizing effect on males, which allows them to function as females.
They also are known to practice coprophagy; eating their own feces (like rabbits, beaver, a few shrews and most dogs). Animals do this to extract extra nutrients from their food, but in the case of wood lice, the reason is to recapture copper. Nearly all crustaceans use a copper-based pigment to carry oxygen in their blood, instead of the more usual iron-based pigment hemoglobin.
It’s sad to say, even with over 5,000 species, many of our terrestrial isopods in North America are introduced. The familiar backyard species – sow bugs such as Porcellio scaber and Porcellio laevis, and the common pill bug, Armadillidium vulgare - almost certainly came over from Europe in ships.
Finally, for those who know me, it is well known that I don’t shy away from tasting any number of nature’s own creations. However, I must say I have never tried a wood louse (no one ever dared me). Perhaps, just as well. A renowned British isopodologist (yes, there are such people) has stated, “If you accidentally get one in your mouth, it’s a most unpleasant experience. Basically, it tastes of strong urine.”