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Aquatic Insects

Damselfly or Dragonfly?

6-16-16  damselfy & dragonfly 178A 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.

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Stoneflies Drumming

2-22-16 stonefly 019Stoneflies 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.

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Caddisflies Laying Eggs

9-3 caddisfly eggs & larvae 402Most caddisflies lay their eggs in or near ponds or streams. A very few species (in the family of northern case makers, Limnephilidae) deposit their eggs above the water on aquatic vegetation in a one- to-two-inch-long mass of jelly (some species’ eggs lack the jelly). Up to 800 eggs (the tan spots within the jelly in yesterday’s post) are laid at one time in one mass. Depending on the species, the eggs take from several weeks up to ten months to hatch. These masses are usually situated so that once the eggs hatch, the larvae will drop down into the water, where they will spend their larval and pupal stages.

Caddisflies are closely related to butterflies and moths, and one of the features they have in common is that the larvae have silk glands in their lower lip. Thanks to the ability to spin silk, the caddisfly larvae build portable cases or attached retreats out of natural material that is available. Some species build elongate tubes out of pieces of plants, sand, sticks or pebbles and reside in them while they drag them along with them wherever they go. Other species attach their cases with silk to crevices in or the bottom of stones in streams. Each species of caddisfly larva always constructs the same type of case, so that you can often tell the genus or even species of caddisfly by the appearance of its case.

The larval stage of a caddisfly can last two to three months or up to two years, depending on the species. Most species spend the winter as active larvae. When it is ready to pupate, the larva attaches its case with silk to something immoveable, such as a large rock. Inside its case, the larva spins a cocoon and eventually pupates inside of it. In two to three weeks the sharp-jawed pupa cuts its way out of its cocoon and floats up to the surface of the water where it emerges as a winged adult, often using its pupal skin as a raft for support during this process. Adult caddisflies live for about 30 days, during which time the males form mating swarms to attract females. After mating takes place, the egg-laying begins.

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Water Scorpions

water scorpion 005These 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.

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Dragonfly Eclosure: A Vulnerable Time

newt eating dragonfly2 021Dragonfly 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.

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Backswimmers Active Under Ice

11-18-13  backswimmers under ice 061Backswimmers are insects classified as “true bugs” and belong to the order Hemiptera. Most Hemipterans are land dwelling, such as stink bugs and assassin bugs, but there are a few, such as water striders, water boatmen and backswimmers, that are aquatic. In the fall, when most insect hatches have ceased, backswimmers come into their own. While some hibernate at the bottom of ponds in winter, others remain active, sculling through the water with their oar-like hind legs that are covered with fine hairs, preying on all forms of life up to the size of a small fish. Thanks to bubbles of oxygen that they obtain from pockets of air just under the ice and carry around with them like mini aqua lungs, backswimmers can continue to stay below the surface of the water for several minutes. Like most aquatic insects, backswimmers supercool their bodies (produce antifreeze compounds called cryprotectants that allow their body fluid to go down to 26 to 19 degrees F. without freezing). Right now, when there’s a thin layer of ice on most ponds and no snow covering it, you might want to peer through the ice at the edge of the pond to see if you can locate any of these cold-hardy creatures. Just be sure you don’t fall in, as I did two seconds after this photograph was taken. My undying gratitude for those of you who have donated to Naturally Curious, as your support enabled me to replace both camera and lens!

Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.


Spreadwing Damselflies Mating & Laying Eggs

10-18-13 spreadwing damselflies 019Believe it or not, there are still damselflies (and dragonflies) that are flying, mating and laying eggs in the middle of October in northern New England. Certain damselflies known as “spreadwings,” unlike most other damselflies, perch with their wings partially open. (Another tell-tale spreadwing sign is that they often perch at roughly a 45 degree angle.) Spreadwings are weak flyers, and you usually see them flying low and for short distances. When sexually mature, the males tend to spend their days perched on vegetation along a pond’s shoreline. The females, like most dragonflies and damselflies, return to the water only when ready to breed. The pictured spreadwings (Spotted Spreadwings, Lestes congener, I believe) are one of the latest species of damselflies active in the fall; these two were resting before resuming egg-laying. The male (at top of photo) grasps the female’s “neck” (to prevent other males from replacing his sperm in her) while the female uses the sharp ovipositor at the end of her abdomen to slice into emergent vegetation and lay her eggs, which eventually end up in the water when the plants die.