Aquatic Life:

Arthropods - Arachnids

Arthropod means jointed foot and is a good general description for the organisms that belong to this phylum. Arthropods are typically classified according to the number of legs they have. The classes that we recognize are the centipedes, millipedes, arachnids (spiders, mites, ticks, scorpions), crustaceans (crayfish, crabs, lobsters), and insects (beetles, flies, wasps, butterflies, etc.). Because we could spend a couple of years talking about every aquatic arthropod we will only focus on some of the more noticeable and significant species.

Arachnids all have four pairs of legs. The two arachnids that are most common in streams, ponds and lakes are fisher spiders and water mites.   Fisher spiders, also known as water spiders, are related to wolf spiders that are the largest and most common spiders in our area. These spiders, unlike other species, have good vision and actively hunt and pursue prey. They do not build webs to catch prey as other spiders do. These spiders are amphibious and are usually found in moist areas, especially along edges of streams and lakes. Fisher spiders can skate across the surface of the water and can dive beneath the surface to feed on aquatic insects, tadpoles, and small fish. Their primary food source is large terrestrial insects found on vegetation near the water’s edge. Fisher spiders can bite humans but are not dangerous. A bite from a fisher spider would probably result in some very minor swelling and itching and that would be it.

The other arachnid that might be encountered in our freshwater ecosystems is the water mite. Water mites are very small, measuring from 1 to 5 millimeters. They look like fat little spiders with round, flat bodies. They have four pairs of hairy legs for swimming.   Water mites swim in slow-moving and shallow water among plants, occasionally attaching themselves to other aquatic animals. They eat plant or animal substances, decaying organisms, and organic material in sediments.   Some adult species can be parasitic and feed on the animals to which they attach. They are not harmful to humans. Water mites do not have a high tolerance for pollution. They are sensitive to changes in their environment and are therefore an important indicator species of aquatic ecosystems.