Monday, December 11, 2017

Mating Snails

White-lip globe snail

We encountered these snails clinging onto a sycamore leaf in the midst of mating last week.  Chris Barnhart identified them as  white-lip globe snails, Mesodon thyroidus, members of the Polygyridae familyThey are land snails, species that left the water and lost their gills long ago when they evolved into air breathers. They are equipped with lungs and are therefore called pulmonate.  In case you have forgotten some of your snail anatomy I've attached a reminder below.
When we first saw this pair there was a bright blue band connecting them, their intertwined copulatory organs filled with their blue blood.  By the time I had my camera out they had separated, leaving their pale white organs dangling, but Alan Cresslor caught a pair like ours in flagrante delicto in the photo below.  The whole subject of snail reproduction gets very complex and I won't get into their love darts which are not fodder for a family blog like ours.

Mating white-lip globe snails - Alan Cresslor
Most land snails are hermaphrodites, equipped with both male and female organs.  Some species may reproduce without mating but other species like our M. thyroidus transfer their sperm to the vagina of another snail via the penis seen above.

We kept these snails long enough to get them to the WOLF School.  I followed one attempted escape as it climbed the wall of a small plastic aquarium.  In the midst of its journey it deposited a small green pile, then crawled over it.  The opening on the left (the snail’s right) is the breathing pore (pneumostome).  Its anus is located in the pneumostome!  We are talking bad breath!  Chris Barnhart tells me that "they often stand on the feces like that. I’m not sure why, but it might have something to do with recovering salts. They can absorb ions through the foot."

When you move as slowly as a snail, you can't be too particular about what you eat.  Most tend to be omnivores eating plant material, fungi, and anything in their path.  Some snails are even predatory!  Our little friends have been rasping away at the tops trimmed off of our sweet peppers.  They use their radula, a tongue equivalent with rasp-like teeth built for scraping the surface of food into the esophagus, but even here there is tremendous differences between species.
"The radula is a membrane covered with series of tiny teeth made of chitin, so it is coarse like sandpaper. The shapes of these small teeth are used to help identify some snail species. However, the teeth of the radula should not be confused with denticles in the aperture of a snail’s shell, which are often referred to as “teeth” as well.
The radula is drawn over a ridge of cartilage (the odontophore), somewhat like a chainsaw chain slides around its bar - though it moves back and forth rather than in a circular motion. Bits of food are broken off and drawn into the snail’s esophagus for digestion. Several bouts of crawling and feeding can occur during an outing.
If you allow a larger snail to crawl on your hand, you may be able to feel it “taste,” or rasp, your skin – the sensation is painless, but feels like a cat’s licking."  Carnegie Museum of Natural History

Don't put snails on the table cloth.
And now the slime.  It was best demonstrated on a colored tablecloth which one of our snails escaped to after climbing out of the aquarium.  Note to self:  Close top of aquarium to maintain domestic harmony.  Since leaving its aquatic origins, preservation of its water has become critical.  A snail's slime is essentially mucous composed mostly of water protecting it against evaporation.  The slime can serve as a lubricant or an adhesive.  When one of our snails tried to escape across the table it left a trail of adhesive slime that lifted the tablecloth when I tried to pick it up.   The chemistry can be far more complicated as in the common garden snail, Cornu aspersum.
In the case of Cornu aspersa, the discharge is composed of synthesized products from various types of secretory glands. These are all single cell glands found in connective tissue and secrete their products via pores that pass between the epidermal cells. They are of various shapes and usually have a long excretory duct. There are eight different types of secreting glands. Four of these different types of mucus secreted protein, calcium, pigments, and lipids.  Wikipedia
There is a sinister side to little snails like this.  Brainworm, Parelaphostrongylus tenuis, is a parasitic nematode commonly affecting the brain of white-tail deer.  The worm lays eggs in the meningeal tissue of the deer which pass into the lungs where they hatch.  The larvae then are coughed up and swallowed, and eventually passed out in the feces.  Slugs and snails pick up the larvae which live in them as intermediate hosts until the mollusks are eaten by deer, starting the cycle again.  They pose no risks to the snail or humans.

The End
Our snails are now living under a large rotting oak log, hopefully rasping away at fungal hyphae and sharing the story of their visit with the 5th grade class.

Chris Barnhart shared this extensive set of photographs of Sonorelix sp. desert snails mating.

The Living World of Mollusks
More on the White-lipped Globe Snail is in this
University of Florida link.
Gastropod reproduction
Snail anatomy, the source of the diagram above.

Friday, December 8, 2017

Luna Caterpillar Molting

Luna moth caterpillar molting - Linda Bower
One of the perks of volunteering with the Butterfly House is the opportunity to raise moths.  The caterpillars devour the leaves they've been given, and when their exoskeletons grow too tight they crawl out of their skin (molting), and emerge in a new stretchy outfit to grow into. They go through five instars (molts) until they finally form a pupa.

Most of us don't have the patience to watch the entire process and find only the old discarded skin (exuvia) if even that.  Linda Bower has saved us the time by filming this great action video of a luna moth caterpillar (Actias luna), molting.  You won't want to miss a single highlight so here is a viewer's guide.
  • It starts with closeup views of the head and mouth which opens briefly.
  • At 0:12 we see a full length view with its two hind prolegs attached to a silk pad.  The pale green head has emerged and its dark former face sits on top like a hat.
  • By 0:37 it starts to rapidly shimmy out of its old skin.
  • At 1:08 the old face skin is displaced, hanging on until 1:31 when it falls off.
  • At 2:00 - free at last!
By 2:32 the caterpillar turns around to eat the discarded exuvia, the first meal in its new clothes.  Energy is precious at this stage and there is no need to miss a free meal, even if it was the old hand-me-down exuvia.
Linda Bower is a member of our Master Naturalist chapter and a frequent contributor to the blog.  Her videos of a number of nature subjects are available at her Youtube channel, Nature in Motion.

Tuesday, November 21, 2017

Life on a leaf

When I find signs of life on a leaf, it usually follows me home.  Stored on our table (thanks, Barb) it can wait weeks before there is an answer, if any. Here are some examples.  A yellow spot on the underside of a maple leaf turned out to be eggs.  I stored them on August 24th and expected to see some larvae emerge but when I checked them on October 17th we had lots of little adult bodies gone past their prime.

Chris Barnhart explained that they had been moth eggs laid in a cluster, possibly oakworm moth eggs of Anisota spp.  Instead they had hatched parasitoid wasps, likely chalcid wasps.  These are parasitoids attacking the eggs or larvae of a large number of insect families.  They tend to be black or brown, often metallic, and have reduced veins in their wings.

Barb brought in this leaf of kale from the garden with cocoons attached.  They soon hatched out these tiny wasps.

Chris explained that they are braconids, probably Cotesia.  They have a distinctive black stigma on the forward edge of their wings.  The larvae can choose to leave the caterpillar entirely and cocoon in a mass.  Bugguide has several examples of these cocoon collections with no evidence of the parasitized larvae left.

Braconid wasps - Microgastrinae - Joy Markgraf 
If you like raising tiny insects and have an understanding spouse or roommate, wasp parasitoids may be for you.  Start looking on leaves.
A number of you have mentioned the late Monarch migration we witnessed this year and asked what it meant for the population.  Here is the opinion from the expert from Monarch Watch.

Saturday, November 18, 2017

Aphids on a Dock

On the MN training field trip to Henning Glade, Becky Swearingen and others found a prairie dock, Silphium terebinthinaceum, flower head covered with orange dots.  These were aphid larvae with an occasional adult, crawling all over the stem.  In the middle of the scramble there was a long flat area with a lot of "stuff" on it.  On closer inspection, this was the protective cover on the back of a debris-carrying lacewing larva.

We described these lacewings in a past blog but I took this one home with me for pictures.  When I opened the little insect box the next day, it was a scene of aphid carnage.  There were over 30 aphid carcasses scattered about, sucked dry by the lacewing larva.  It was interesting that during the feeding orgy within the confines of the little box it hadn't made any attempt to decorate its back with debris as it had the day before.

There are several possible explanations for this "naked" lacewing.  Some aphid colonies are protected by ants in a symbiotic relationship.  The ants get aphid honeydew and the aphids get protection from bullies like these lacewing larvae.  Thomas Eisner removed debris from some of their backs and showed that decorated lacewings could invade an aphid colony while naked ones were repelled.  It may also be that the day before it was just covered by crawling aphids.

Our Master Naturalist videographer Linda Bower has this clip showing a green lacewing larva grabbing an aphid (at :32 seconds) and then sucking away, earning its name as an aphid lion.

Monday, November 13, 2017

Horntail Technology

This insect caused quite a stir when found on a tree at the WOLF playground because of its prominent "stinger."  Although it looks dangerous, it is actually harmless unless you happen to be a tree.

Wasp stinger with venom drop - Wikipedia CC
This is a horntail wasp of the Siricidae family, another example of a wasp without a stinger.  The 20,000 plus species of solitary wasps do not have stingers.  Social wasp females such as the yellowjacket have their ovipositor modified to sting defensively, delivering a dose of venom to remind you of it for longer.

Horntail and ovipositor - Barry Stewart

Siridicae's "horntail" seen above is really decorative, of no known purpose except to scare us.  The female's ovipositor is beneath and much more flimsy looking.  It uses it for the original purpose, in her case injecting an egg into wood.  Imagine the pressure required to push a pin or needle into wood and compare it to the lightweight wasp body.

Urocerus albicornis - Eric Adams
The ovipositor overcomes the weight problem by mechanics.  First, the ovipositor lies inside a sheath that absorbs most of the pressure.  She will probe the wood in several places, finding a soft spot to inject the egg with fluid.  It contains a fungus that she carries in an abdominal opening.  The fungus will attack the wood while the egg matures, providing the newborn larva a predigested meal. 
Ovipositor with sheath on either side - Stanislaw Kinelski, CC
The story gets even better.  Many species of horntails have zinc in their ovipositors as well as in the adult's jaws, hardening them for chewing out of their wood incubator when they emerge as discussed in this previous blog.  In addition, the horntail ovipositor design has inspired new medical instrumental technology as described in Materials World Magazine:
"The wood wasp’s ovipositor looks like two hollow needles, one inside the other, each of which is lined with backward-facing teeth to give purchase as the wasp ‘drills’ progressively into the bark of a tree. This takes surprisingly little force, making it attractive for carrying out minimally invasive procedures such as brain biopsies without having to exploit a natural orifice."
The only significant damage they cause is if a board used in your house construction contains the larva.  When the adult emerges from its pupa it will chew its way out through wood, plasterboard or even a plastic covering.  Please forgive it and understand what a cool insect is visiting your house.
More at blogs by Bugeric and the Bug lady.

Saturday, November 11, 2017

Asian Ladybugs

This story starts with an inquiry from Lori Herring and her 2nd and 3rd grade students at Marshfield R1 School.  They were studying trees and found the maple leaf above with something on it they couldn't identify by field guides.  A first guess was an Asian ladybug larva but there was more to the story.

Early larva

Zooming in you can see a little beyond halfway down that the larva is splitting its skin down the back to expose the pupa.  Notice the spiky features at the front, the remains of the last larval stage to the right.  This is the last step in its metamorphosis before it emerges in the fall to start to torment us. describes this step in the life cycle: 

"When the larva has grown to its full size it will then attach itself to the stem of a plant. It splits along its backside and exposes the pupa underneath. This sounds like something out of one of the “Alien” films and it really doesn’t take long to figure out that they didn’t get those ideas straight out of their imagination! The pupa, though, is wrapped up in this final stage of its metamorphosis and so is safe from the elements – but not from predators. It is at this stage it is at its most vulnerable. If approached close to its hatching time by a possible predator it will shake itself dementedly to try and warn off the unwelcome visitor! This last stage takes just a few days and then the adult ladybug is ready to emerge."
Larval stage
Now back to the "torment."  This is the Asian ladybug, Harmonia axyridis, actually a beetle as all "ladybugs" are.  It is most commonly known as the harlequin, multicolored Asian, or simply Asian ladybeetle in the Coccinellid family.  Unlike our "ladybugs" beloved in children's stories and merchandise, these are no "ladies."

Last week, shortly after the first hard freeze of the year we had the sudden return again of swarms of these ladybeetles on the sunny side of the house, the trees and my neck.  There are those annoying little nips on the neck and arms and when I swat or brush them away I am left with a stink on my hands.  Why now?  Tim Smith answered the question in the Missouri Conservationist Ask the Ombudsman column several years ago.
"Each fall, during a warm-up following the first cold weather, the insects gather on the sunny sides of houses and other structures as they look for cracks and crevices where they can find shelter from the coming winter.  Many will survive the winter and appear again in the spring as temperatures warm and they try to exit the house."
According to Wikipedia, they were brought to the United States in 1916 to control insect pests of plants, but were not successful.  In 1988 they were observed in numbers in New Orleans, and since then they have spread.  By 1995 they were occasionally found in the Midwest and became common in 2000.

They cluster by the hundreds in protected spaces
Subsequently, they have also contributed to the decline in native ladybugs, presumably by out competing them.  They also have reached pest status to the higher biped mammals, i.e. us, both because of the swarming numbers, their little bites and unpleasant odors and the tendency to move into our buildings.  For information on these pests including control recommendations, check out this Ohio State site.
=== has detailed photographs of their various life stages from egg to annoying adult.

Thursday, November 9, 2017

This is a Bug?

Green Stink Bug

A student found this on the WOLF School field trip to Bull Mills and announced "I caught a mosquito!"  My first guess was crane fly, but I wasn't even close.  This is a stilt bug, aka thread bug, a member of the Berytidae family of Hemiptera or true bugs.  With their slender bodies and thin legs I would never have guessed they are related to other Hemiptera like stink bugs.

In addition to their svelte physique they have several distinguishing characteristics.  Their femurs (the leg segment nearest the body) have a swelling at the distal end.  Also their antennae are geniculate (elbowed - your word for the day) and have a slightly bulbous tip seen below.

Very little is known about their habits.  Although they are said to be common on plants in the spring, most are less than a half inch long, have little color and move slowly so they are hard to see.  While many are thought to be plant eaters, especially those plants with sweet hairs, some may be omnivores, eating plant bugs and their eggs.*

Despite the mosquito-like appearance they don't sting, bite or land on us deliberately.  Incredibly, they are said to overwinter as adults, without a drop of insulating fat on their body!  Googling 80 links didn't bring up any more details so I suggest you simply enjoy the pictures.

* The Bug Lady at Field station
 Shelly covered them at MoBugs in 2010.