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Another Aquatic Insect article by Rick HafeleINVERTEBRATE SEX - IS IT SAFE? |
The morning sun began to send a warm glow from the tips of my
cerci down to my last tarsal segment. I stretched. My wings felt stiff at
first, but then, as the warmth spread deep into my thorax, they twitched
eager for flight. No one told me, but I knew I didn't have long to find a MAYFLIESThere are no animals I can think of that have so thoroughly focused on sex as mayflies have. The dun, or subimago, wiggles free from its nymphal skin at the water's surface mouthless, unable to eat or drink the slightest morsel or smallest drop. Without any way to eat or drink, organs for digesting food are not needed and would only be in the way. In this way the females' abdomens are completely packed with eggs, all energies concentrated on procreation.Duns, however, are not sexually mature and are unable to mate. As soon as they fly off the water they head for the foliage along the bank where yet another behavior unique to mayflies takes place. After a period of a few hours to several days, depending on the species, the exoskeleton of the dun splits open and is cast aside allowing the true mayfly adult, or imago, to emerge. This stage, known to anglers as the spinner stage, is sexually mature and ready for the final flight. It is the male spinners that form the large swarms over the water. Up and down the males dance over a shallow riffle or run waiting for a female to fly into the swarm. When a female enters she is quickly seized from below by a male. The male's long front legs hold her thorax andspecial claspers at the tip of the males abdomen hold her abdomen during copulation. Mating is short and sweet! In a matter of seconds the male releases packets of sperm into a special organ (spermatheca) inside the tip of the female's abdomen. The two separate and the female may immediately begin laying eggs. The eggs are actually fertilized as they pass by the spermatheca as they are being laid. As described above mayflies mate in the air. The time of day mating occurs, however, is quite variable. Weather seems to play the major role in when mating will occur. During cool periods of the year mating takes place during the warmest part of the day, generally between IhOOam and 3:00pm. During the warm days of summer mating may occur in the morning or late afternoon and evening. The middle of the day is generally too hot, but on cool overcast summer days mating swarms still may be seen in the afternoons. Most mayflies lay their eggs on the surface of the water. The female glides down and just touches the surface which washes off a small cluster of eggs. This action is repeated perhaps a dozen times until all the eggs have been laid. Some species, however, crawl down underwater along the sides of rocks to lay their eggs. The common Blue-winged Olive or Baetis species often lay their eggs in this fashion. Anywhere from 500 to 5,000 eggs may be laid per female. All mayflies have a short adult life, but how short varies considerably with the species. One of the longest lived groups is the genus Callibaetis. In this genus the females incubate the eggs for five or six daysafter mating. When the eggs are laid they hatch immediately. Female Callibaetis have been kept alive for up to thirteen days in the laboratory. On the other end of the scale is the genus Ephoron, a burrowing mayfly in the family Polymitarcyidae. Male Ephoron molt from dun to spinner within a few minutes after emerging. Females don't even molt into the spinner stage, mating instead as subimagoes or duns. Their entire adult life lasts no more than an hour! STONEFLIESStoneflies have a quiet sex life compared to the wild aerial orgies of mayflies. Nymphs crawl out of the water onto shoreline rocks or vegetation just prior to adult emergence. This occurs at various times of the day, but often at night. Adult stoneflies have useable mouth parts, however, their feeding is often restricted to just water or pollen and nectar from streamside flowers. The length of adult life is variable. Some species may live only four or five days, and others four or five weeks.Ten to fourteen days is a typical life span for most stonefly adults. Stoneflies mate on the ground or streamside foliage rather than in the air. One of the most interesting mating behaviors of some stoneflies is how they attract their mates. It could be called the Buddy Rich approach. That's right they do it by drumming. The next time you see a large male stonefly adult, turn it over and look at the last few segments of its abdomen. On many species they will be swollen and quite hard. Entomologists refer to this as the "hammer." The hammer is beat on a hard surface like a tree branch with a drumming effect. Females will sometimes answer the male with their own drumming signal. This behavior has been directly linked to mate selection and the initiation of copulation. After mating females no longer respond to the drumming of a male. (I wonder if this is why my own drumming has been attracting fewer females over the years?) Male Stoneflies also have some amazingly shaped reproductive structures. Epiprocts, paraprocts and aedeagus are the names given to these structures. Epiprocts and paraprocts are variously shaped claspers for holding on to the female, and the aedeagus is the insect equivalent of a penis. If you have a hand lens, or better yet a microscope, collect a few male Stoneflies and take a look. You'll have a new appreciation for the creativity of nature. CADDISFLIESCaddisflies combine some behavior of both mayflies and Stoneflies. Adults emerge at the water's surface like a mayfly dun. The adult caddis then fly off the water to vegetation along the banks where they mate on the foliage like stonefly adults. Caddis adults feed on liquid and nectar, andgenerally live three to six weeks. Some species that inhabit intermittent streams live all summer as adults waiting for fall rains before laying their eggs. Some of the more interesting and important behavior of adult caddisflies is how they lay their eggs. Many species important to anglers, like the net-spinning caddis (Hydropsy che), green rock worms (Rhyacophila), and turtle-case caddis (Glossosoma), lay their eggs by diving underwater instead of releasing them at the water's surface like most aquatic insects. The females of these caddis have enlarged and flattened hind legs which are used for swimming. The females fly out over the water, and then from several feet up dive straight down through the surface film. Once underwater they use the hind legs like small oars and swim quickly down to some rocks. There they lay strings of eggs. After all their eggs have been deposited they let go of the rock and swim back towards the surface. This activity is often heavy in the afternoon or evening and creates some obvious opportunities for fish and anglers. This behavior may also explain the success of many old wet fly patterns fished with a rising motion through riffles and runs. DRAGONFLIES & DAMSELFLIES ( ODONATA )Dragonflies and damselflies have perhaps the most elaborate and complex mating behavior of any of the aquatic insects. First of all adults tend to be long lived. This means several weeks to several months. All actively feed as adults. Small flies including mayflies, chironomids (midges), and especially mosquitoes are eaten readily by adult dragonflies and damselflies. Food is typically captured and consumed in flight. Dragonflies are especially strong fliers. They are able to hover, fly backwards or sideways and reach speeds over 35 mph!Mating begins with males setting up mating territories. Other males of the same species are recognized and chases away using a variety of behavior. Aerial displays which include confronting the intruding male and raising the abdomen above the head, to actual physical fighting will be used. The attacker approaches from below and the individual being attacked often maneuvers in a spiral downward flight to get below its attacker. Older males often look quite tattered after days or weeks of guarding their territory from other males. When a female flies into the mating territory, however, the males response is quite different. Visual cues are the main way adults recognize males from females, though distinct differences in flight patterns between males and females are also important As a result males and females frequently differ in color. Males may show distinct courtship behavior when a female enters his territory. Some fly directly in front of the female wagging the abdomen from side to side. Others may fly in semi-circles around and below the female. In still other species the male may perform a kind of dance in front of the female before copulation. Prior to copulation the male first transfers sperm packets from the tip of his abdomen to an accessory organ located on the ventral surface of the second and third abdominal segments. Once a female shows she is responsive to mating the male holds the female from above until he engages specialized claspers at the tip of his abdomen into grooves behind the head of the female. At this point the male lets go with his legs and lifts the female into the air. The female then rotates her abdomen under the male until it contacts the male's accessory organ. This is referred to as the wheel-position. Depending on the species adults may stay in this position for only a few seconds upto three for four hours. When the female releases her abdomen from the male's accessory
organ the male often continues to hold the female while she lays her eggs.
Some females remain underwater for an hour or more while laying eggs in
the stems of aquatic plants. In this case the males often patrol the area
above the female keeping other males and ovipositing females away. In
this way overpopulation of a specific site may be avoided. |
I have found fly fishers to be terrible romantics. Why else would we
spend hundreds of dollars on old cane rods, or fondly show off skins from
road kill animals, or keep boxes of useless worn out flies tucked away in
our tying desks? This romantic tendency also creates much discussion and