Showing posts with label life cycle. Show all posts
Showing posts with label life cycle. Show all posts

Friday, July 10, 2015

Fly Day Friday: Rat-tailed Maggots

I recently started working part-time at Songbird Supplies, LLC, located inside Summerland Gardens here in Colorado Springs. One of the perks has been encountering insects I seldom see. Julie, the proprietor of Summerland Gardens, called me over the other day to help her identify a "primordial soup" bug in one of the water gardens she is cultivating. I was surprised and delighted to find the critters in question were "rat-tailed maggots," the larvae of flower flies in the tribes Eristalini and Sericomyiini (subfamily Eristalinae, family Syrphidae). I had seen them maybe one other time previously.

The conundrum faced by folks with water container gardens is this: do I put in "mosquito dunks" to kill the mosquito larvae, or do I refrain so that the syrphid larvae can grow up into pollinator-capable adult flies? There is no right or wrong answer. Syrphid flies are definitely not endangered species, so I might deploy the dunks.

Note the leg-like "knobs" along the length of the body of the rat-tailed maggot on the left

The rat-tailed maggots are named for the posterior spiracles, which are fused into an extensible breathing siphon that connects them to the water surface at all times. Meanwhile, at the other end, they are filtering bacteria and other microbes from organic matter in the water. Larvae of some species exist in rather dense material like saturated manure, which barely qualifies as aquatic, but is too wet for other dung-eating fly larvae. The low oxygen levels in this kind of substrate are no problem because the maggot's spiracles are always connected to the surface.

The length of the "snorkel" varies greatly depending on the genus of flies. Eristalis larvae have very long tubes, as shown in the images here; Chrysogaster falls at the other end of the spectrum, with quite a short siphon.

Different genera occupy different aquatic niches. Mallota and Mylopeta, for example, live in the water that collects in tree holes. Sericomyia larvae live mostly in bog mat pools. Chrysogaster thrive along the edges of ponds and among emergent vegetation. The most commonly-encountered species are probably in the general Eristalis, Eristalinus, Helophilus, and Palpada, since they are most likely to be seen in urban, suburban, and rural areas. They live in putrid and organic-rich standing water. I know they are sometimes found while cleaning rain gutters.

Once the larva reaches maturity, it seeks dry land on which to pupate. Teh pupal capsule is hard, and resembles a tiny mouse in shape.

Adult Drone Fly, Eristalis tenax, Colorado

The "Drone Fly," Eristalis tenax, is the most common adult version of a rat-tailed maggot that one is likely to see. It is a stunning mimic of the honey bee. Likely introduced ages ago from Europe, it is now an established and widespread species across the entire North American continent. It is also a fairly respectable pollinator, visiting wildflowers, and the blossoms of orchard trees and landscape plants.

Here is an interesting piece of trivia: It is speculated that it was rat-tailed maggots that gave rise to the biblical account of "bees" spontaneously appearing from the rotting carcasses of animals. Certainly, the fluid decomposing material in a corpse would be a perfectly acceptable habitat for Drone Fly larvae.

Adult male Eristalis tenax, Arizona

Sources: Carr, John F. 2013. "Rat-tailed Maggots," Bugguide.net.
McAlpine, J.F. (editor). 1987. Manual of Nearctic Diptera Volume 2. Ottawa: Agriculture Canada. Monograph No. 28. pp. 675-1332.
Merritt, Richard W. and Kenneth W. Cummins. 1978. An Introduction to the Aquatic Insects of North America. Dubuque, Iowa: Kendall/Hunt Publishing Company. 441 pp.
Pfiester, Margaret, and Phillip E. Kaufman. 2009. "Rat-tailed Maggot," Featured Creatures. University of Florida Department of Entomology and Nematology.

Monday, April 25, 2011

Giant Silkmoths

We were fortunate to have hosted three species of giant silkmoths (family Saturniidae) in Butterfly Magic this year. They are spectacular insects, but so unique and short-lived that one cannot generalize to moths as a whole from their life cycle and behavior.

Estimates differ as to how many species are in the Saturniidae, but somewhere between 1,300 and 1,500 is fairly accurate. Gene sequencing could result in more or fewer species than currently recognized. Giant Silkmoths are found the world over in forest habitats, but are especially diverse in the neotropics (Mexico, Central and South America). You are probably already familiar with some U.S. species: the Luna Moth, Cecropia Moth, Polyphemus Moth, Royal Walnut Moth, Imperial Moth, and Cynthia Moth. Not all the silkmoths are giants. Buck moths (genus Hemileuca) are much smaller, and fly during the day.

The adult moths do not feed. They have vestigial mouthparts at best and fuel their flight on fat reserves accumulated as caterpillars. Consequently, the caterpillars of giant silkmoths are large and heavy at maturity. The “hickory horned devil,” larva of the Royal Walnut Moth, approaches the size of a frankfurter. It looks menacing but is harmless.

Meanwhile, the larvae of other silkmoths are studded in venomous spines. Beware the caterpillars of buck moths (I can attest from personal experience!), the io moth, and especially the South American Lonomia (see also more recent articles in medical journals).

The Forbes Moth, Rothschildia lebeau forbesi, is frequently mistaken for an Atlas Moth by our visitors. Both species have “windows” in their wings that are devoid of scales. The Forbes Moth ranges from the Lower Rio Grande Valley through much of eastern Mexico and south to Brazil. Relatives of this moth figure prominently in the culture of indigenous peoples. Bushels of cocoons are harvested to make rattles worn on the ankles during ceremonial dances.

The African Moon Moth, Argema mimosa, occurs over most of sub-Saharan Africa. Their cocoons are distinctive: compact, and made of dense silk with numerous small perforations. The adult moths are spectacular: a wingspan averaging 125 mm, yellowish green in color with long, streaming “tails” on the hindwings. What purpose those tails serve is open to speculation, but perhaps it further camouflages the insect when it is at rest among foliage.

Last but not least is the Atlas Moth, Attacus atlas, a real giant with a wingspan of 240 mm (compare that to the Forbes Moth, only 90-100 mm from wingtip to wingtip). The Atlas Moth is widely distributed, from India to Hong Kong, tropical Asia in general, plus Taiwan and Indonesia. The front wings have a conspicuous lobe with markings that suggest the head of a serpent, but whether this is real mimicry or not is debatable.

The adult females of all the silkmoths rarely stray far from their cocoons after emerging. They invest most of their energy in egg production, so instead of exerting calories in flight, they simply sit and emit a species-specific sexual attractant called a pheromone. This scent, while usually imperceptible to us, is potent when it comes to drawing males. The males, with broad wings and streamlined bodies, use their sensitive antennae to home in on the pheromones, following the scent trail up to a mile or more to find its source. Females, once mated, will then finally fly to appropriate host trees and deposit their eggs. Even unmated females will dump their eggs in great quantities, as is often seen in our greenhouse. Both genders live only a few days, assuming they can avoid predation by bats.

Breeding silkmoths in captivity is becoming quite the hobby and cottage industry. My friend Liz Day has a web page devoted to helpful hints for rearing common eastern U.S. species. Considering the threats faced by these magnificent moths, from suburban sprawl and light pollution to introduced parasites, our domestic species could use some help.

I would like to conclude by recommending Wings of Paradise by John Cody, published by University of North Carolina Press, 1996. Cody renders giant silkmoths in stunning watercolor paintings. He features all three species in the greenhouse, plus scores more. The art is complemented with anecdotes and factual information.