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Odonata

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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Dragonflies Eclosing

5-26-16  dragonfly eclosing2  347 The sudden hot weather seems to have triggered a mass emergence of dragonflies and damselflies.  The emerging vegetation along the shores of ponds is covered with larval Odonates (members of the order of insects that includes dragonflies and damselflies) metamorphosing into adults.  The adults, still in the skin of their last larval stage, crawl out of the water, climb up vegetation, rocks, etc., and split the back of their larval skin.  The adult flips backwards out of this opening, hangs upside down and then grasps the vegetation and/or empty larval skin while as its abdomen is released.  The dragonfly hangs in the breeze while it pumps air into its body, sending liquid into its wings.

To appreciate this process called eclosion, compare the size of the wings in the photo insert (recently-emerged adult) with those in the larger photograph, which was taken twelve minutes after emergence.  Within a day or so the sheen on the newly-formed wings goes away, the dragonfly’s body hardens and colors start to appear.

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Darners Laying Eggs

9-1-15 dragonfly laying egg 135Females of different species of dragonfly have different techniques for laying their eggs. Most skimmers, cruisers and clubtails dip the tip of their abdomen to the surface of the water while hovering or flying, and release their eggs. Most darners, such as the Shadow Darner (Aeshna umbrosa) pictured, have a sharp-edged ovipositor with which they slit open a stem or leaf of a plant on or near the water. They then push their egg into the plant tissue exposed by the slit. Because they are stationary during this process, female darners are vulnerable to predation by fish and frogs at this time. A close look at the bottom third of cattail leaves this time of year will tell you whether or not darners are in the vicinity, as the slits they make are very apparent, appearing as thin, tan, 1/2″ vertical lines.

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Dragonflies & Damselflies Spear Prey With Lower Lip

7-27 dragonfly mouthpart 077Dragonflies and damselflies are unique among aquatic insect larvae in that they have a greatly enlarged hinged lower lip, or labium, which they can rapidly extend outwards to capture prey. When retracted, the prehensile labium fits like a mask over the face or is folded flat beneath the insect’s head. When hunting for prey, the dragonfly larva uses its labium like a speargun. It shoots forward as far as half the larva’s body length away, and moveable hooks on the front edge grab the prey. There are no muscles at the hinge/joint, leading entomologists to believe that the labium is extended by increased blood pressure caused by abdominal muscle contraction. It unfolds at a right angle, and extends extremely rapidly, faster than most prey can react. (photo: cast skin of dragonfly larva from which adult dragonfly emerged)

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Meadowhawks Mating & Laying Eggs

9-30-24 autumn meadowhawks laying egg  043There is a genus of dragonflies, Sympetrum, referred to as meadowhawks, which emerge and fly in late summer and autumn, breeding in ponds and foraging over meadows. Mature males and some females of certain species of meadowhawks become bright red on part or all of their bodies. When breeding, the male grasps his mate behind her head with the appendages at the end of his abdomen and often does not release the female until after she has laid her eggs, which she typically does by dipping the tip of her abdomen in the water (see photo). The reason for this continued connection is related to the fact that a male dragonfly may remove sperm present in the female from any previous mating and replace it with his own packet of sperm, or spermatophore. In order to prevent this from happening, and to assure his paternity, a male dragonfly sometimes flies close to his mate, guarding her while she lays her eggs, or, in the case of meadowhawks, may fly in tandem with the female throughout the egg-laying process.

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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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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.


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