If you see what look like miniature water striders skating on the surface of a stream or pond, you may have come upon an aggregation of Broad-shouldered Water Striders, a different family of water striders from the ones we commonly see. They are tiny (2-6 mm) and very fast-moving, zipping here and there with the speed of a bullet, staying on top of the surface film, or surface tension, that is created by the attraction of water molecules. Adaptations to this mode of travel include non-wettable hairs at the ends of their legs that don’t disrupt the surface tension, and claws that are located a short distance up the outermost section of their legs rather than at the end of their legs, so as not to break this film.
Broad-shouldered Water Striders are often found in the more protected areas of a stream, where they tend to congregate in large numbers. Members of a common genus, Rhagovelia, are known as “riffle bugs” and are often found below rocks that are in the current. Broad-shouldered Water Striders locate their prey (water fleas, mosquito eggs and larvae, etc.) by detecting surface waves with vibration sensors in their legs. There can be up to six generations a summer (photo shows that they are still mating at the end of October). Broad-shouldered Water Striders spend the winter hibernating as adults, gathering in debris at the edge of the water or beneath undercut banks.
A favorite past-time of mine is peering under logs and rocks to see what might be living there. (The logs and rocks are carefully replaced in the position in which they were found so as not to disturb the inhabitants any more than is necessary.) Recently I discovered a Crane Fly larva under a rock that was adjacent to a stream – a typical spot in which to find a soon-to-pupate larva. Roughly an inch long, the most distinguishing features are the ridges along its body, and the star-like appendages at the tip of its abdomen. If you examine the appendages closely, you will find two spiracles, through which the Crane Fly larva breathes, located in a recessed area in the center. Although you can’t see a head, it has one that is tucked into its thorax.
The Crane Fly family is the largest family of true flies, in terms of number of species. They can be found in aquatic, semi-aquatic and terrestrial habitats. True flies do not have segmented legs that they can use to hold on to the substrate when they catch their prey. Many Crane Fly larvae feed on decomposing leaves, but those species of Crane Flies which are predators are capable of forming a large knot with the muscles at the end of their abdomen. When they catch prey with their mouthparts, they enlarge the end of their abdomen and wedge the knot between stones in order to anchor themselves.
A visit to a pond will usually include sightings of dragonflies and the more delicate damselflies. Both of these types of insects are in the order Odonata (Greek for “tooth,” referring to the serrated jaws of the adults). They are separated into two suborders, due to their wing shapes and sizes. The wings of dragonflies differ in shape and size (hind wings are broader than forewings), whereas damselfly fore and hind wings are similar in shape, with the hind wings sometimes being smaller.
In addition to wing differences, damselflies have eyes that are separated by more than an eye’s width, whereas dragonfly eyes either touch or are separated by less than an eye’s width. Damselflies are smaller and more slender than dragonflies and perch with their wings closed over their abdomens or held slightly spread. Dragonflies at rest hold their wings out flat or downward. In addition, dragonflies are more powerful and acrobatic in flight than damselflies.
Although these differences distinguish them, damselflies and dragonflies do have many similarities. Both are carnivorous, both spend most of their lives as aquatic larvae, and both lay their eggs in or near water.
Stoneflies spend the larval stage of their life in streams. When the larvae mature, they crawl out of the streams they grew up in, split their larval skins and emerge as winged adults, ready to mate. Stoneflies are unique among aquatic insects in that there are different species that emerge in all months of the year. Most species mature in warmer months, but some do so during warm spells in winter and there are two families (referred to as winter stoneflies) that emerge only at this time of year, perhaps because of the scarcity of predators.
Recently, perhaps due to the warm weather this past weekend, large numbers of stoneflies emerged. In places, the snowy banks of open streams were littered with half-inch adult stoneflies whose new skins were drying. This entomological exodus from the water typically takes place at night, to avoid being eaten by terrestrial insectivores and birds. After their adult skin dries, winter stoneflies can be seen crawling on top of the snow as they search for a mate.
In many species, male and females locate each other by tapping the tip of their abdomen upon the substrate, a process referred to as “drumming.” Any stoneflies in contact with that substrate will feel the vibrations of this drumming. Male and female drumming patterns are specific for each species and for each sex. Male stoneflies initiate drumming and females answer. This means of auditory communication is closely related to the “songs” of crickets, grasshoppers and katydids. The difference is that the sound waves of the terrestrial insect songs travel through the air and are loud enough for humans to hear, whereas the sound waves of stonefly drumming travels through a solid medium and is inaudible to us.
These stick-like insects can be found inhabiting most freshwater ponds in the Northeast. Although called water scorpions, these water bugs aren’t even closely related to scorpions. Their name comes from the fact that they superficially resemble scorpions, with their modified grasping front legs and “tails,” which act as snorkels or breathing tubes. The long,slender water scorpions in the genus Renata are also referred to as water stick insects or “needle bugs.”
Water scorpions are formidable predators, reaching up to five inches in length. The majority of their diet consists of other invertebrates, but they have been known to take tadpoles and minnows.
Water scorpions mate at this time of year — males produce chirping noises, much like a cricket, to attract females. After mating, the female lays several eggs and attaches them to aquatic vegetation.
Dragonfly larvae reside in ponds until the time comes for them to climb up stalks of emergent vegetation or adjacent rocks, split their larval skin and emerge as adults (a process called eclosure). Before it can take flight, a dragonfly has to cling to the substrate long enough to expand its wings by pumping fluid into them, and dry its exoskeleton as well as its wings. During this time the dragonfly is extremely vulnerable – not only can it not fly, but it is usually situated directly above the water. The slightest breeze can blow it from its precarious perch into the water below, where opportunistic predators such as this Eastern Newt are at the ready and make quick work of their helpless prey.